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Distribution, habitat use, breeding and
behavioural ecology of rainbow skinks
(Lampropholis delicata) in New Zealand
Joanne E Peace
2004
ii
Acknowledgements
This research project was carried out at The University of Auckland.
Without the guidance and encouragement of my superiors this project would not have
taken place. I am most grateful for the time, compassion, humour, and help provided by
Dr Dianne Brunton, Dr Neil Mitchell and Dr Graham Ussher.
Throughout my MSc the time I spent in the Ecology lab was extensive. Thank you for
your help, for being there and being yourselves:
Michael Anderson, Sandra Anderson, Marleen Baling, Paul Barnett, Craig Bishop,
Dianne Brunton, Julia Chen, Dave Clarke, Carol Curtis, Yanbin Deng, Robin Gardner-
Gee, Joshua Guilbert, Melinda Habgood, Charlotte Hardy, James Haw, Carryn Hojem,
Darryl Jeffries, Emma Marks, Kevin Parker, Matt Rayner, James Russell, Dave Seldon,
Rose Thorogood, Sarah Withers, Laura Young, Aiden, Dominic, Stefan.
This project would not have been as successful without the advice and assistance of The
University of Auckland staff, especially certain people from within the School of
Biological Sciences. I wish to thank:
Chris Thoreau, Sandra Anderson, Rachel Chidlow, Terry Gruijters, Sharon Fisher, Kate
Hollard, Karen Jennings, Sandra Jones, Iain McDonald, Percy Pearce, Vernon
Tintinger, Dave Todd, Brian Wilson.
In addition, there are many university services that are both integral and of immense
help and are likely to be overlooked if not mentioned:
Animal Ethics Committee, Cleaning staff, General library staff, Interloans and Inter-
Campus Library Delivery Service personnel, Property Services, Unisafe.
iii
The help and support given to me during this research enabled me to achieve the
research aims. I am thankful to the following people for their assistance and goodwill:
Tony Whitaker.
Brian Gill (Auckland War Memorial Museum).
Daniel Atkinson, Tara Atkinson-Renton, Steve Black, Simon Chapman, Ray Downing,
Janice Edge, Roger Larson, Marc Libeau, Geoffrey Patterson, David Wilkinson
(members and Regional Representatives of the NZ Herpetological Association).
John Adams, Sam Ferreira, John Heaphy, Kent Hunt, Leigh Marshall, Colin Miskelly,
Keri Neilson, Keith Owen, Richard Parrish, Nic Peet, Rosalie Stamp, Mike Thorsen
(staff of the NZ Department of Conservation).
Sites accessed during this project were done so by the kind permission of the following:
Staff at Nervermans Natives and Selmes Road Nursery, Chris, Nigel, Sharon, Mike
Ashby, Julie Blanchard, Dianne Brunton, Sue Daw, Thomas Emmitt, Mark Fordyce,
Sue Hill, Carolyn Jackson, Birandra Singh (Manukau City Council), Rowena & Terry
Storey, Bill & Betty Strothers, Kerry & Kim Thornes, Paul Woodard.
Liz Callinan, Wendy Fisher, John Gould, Brendan MacKay, Trent Taylor (staff of the
Auckland Regional Council).
Throughout my research I have been fortunate to receive the help with many tasks that
would have been a lot less enjoyable without the willing and positive assistance of:
Taneal, Michael Anderson, Marleen Baling, Paul Barnett, Thomas Emmitt, Joshua
Guilbert, Melinda Habgood, Charlotte Hardy, Karl Hewlitt, Darryl Jeffries, Andrew
Jenks, Emma Marks, Matt Rayner, Tim Sippell, John Steemson, Dylan Storey, Rose
Thorogood, Graham Ussher.
I am grateful for the financial support awarded by:
Auckland Regional Council, Bart Baker Memorial Scholarship in Vertebrate Pest
Management, James Sharon Watson Conservation Trust, The University of Auckland.
iv
Table of contents
ACKNOWLEDGEMENTS ii
TABLE OF CONTENTS iv
TABLE OF FIGURES vii
TABLE OF PLATES viii
TABLE OF TABLES viii
ABSTRACT ix
1 GENERAL INTRODUCTION.............................................................................. 1
1.1 Invasive species ................................................................................................... 1
1.2 The rainbow skink (Lampropholis delicata) (Squamata: Scincidae) .............. 5
1.2.1 Distribution 6
1.2.2 Habitat use and general population and morphological parameters 9
1.2.3 Reproductive biology 11
1.2.4 Interspecific interactions with lizards 12
1.3 The copper skink (Cyclodina aenea) (Squamata: Scincidae) ........................ 13
1.3.1 Distribution 13
1.3.2 Habitat use and general population and morphological parameters 14
1.3.3 Reproductive biology 16
1.3.4 Interspecific interactions with lizards 16
1.4 Research objective ............................................................................................ 17
1.5 Thesis plan ......................................................................................................... 17
2 METHODS............................................................................................................ 18
2.1 Introduction....................................................................................................... 18
2.2 General methods ............................................................................................... 18
2.2.1 Environmental data 18
2.2.2 Capture and handling of skinks 18
2.2.3 Data analysis 21
2.3 Current and predicted distribution methods ................................................. 22
2.3.1 Survey methods 23
2.3.2 Data Analysis 24
v
2.4 Population parameters and habitat use methods........................................... 24
2.4.1 Habitat use 24 2.4.1.1 Data analysis 27
2.4.2 General morphological features 28 2.4.2.1 Data analysis 28
2.5 Reproductive biology methods ........................................................................ 29
2.5.1 Data analysis 30
2.6 Interspecific interaction methods .................................................................... 33
2.6.1 Enclosure set up 34
2.6.2 Behavioural observation methods 36 2.6.2.1 Pilot study 36
2.6.2.2 General observation methods 36
2.6.2.3 Focal animal observation methods 38
2.6.2.4 Scan observation methods 38
2.6.2.5 Data Analysis 39
2.6.3 Body condition measurement methods 40 2.6.3.1 Data analysis 40
2.7 Study sites .......................................................................................................... 41
3 CURRENT AND PREDICTED DISTRIBUTION............................................ 49
3.1 Introduction....................................................................................................... 49
3.1.1 Objectives 51
3.2 Results ................................................................................................................ 51
3.3 Discussion .......................................................................................................... 58
3.3.1 Considerations 62 3.3.1.1 Scales of measurement 63
3.3.1.2 Genetic homogeneity 64
3.3.1.3 Future surveys 66
3.3.2 Conclusions 67
4 HABITAT USE AND GENERAL MORPHOLOGICAL FEATURES OF
DIFFERENT POPULATIONS ................................................................................... 68
4.1 Introduction....................................................................................................... 68
4.1.1 Habitat use 68
4.1.2 General population parameters 70
4.1.3 Objectives 71
4.2 Results ................................................................................................................ 72
4.2.1 Habitat use 72
4.2.2 General population parameters 75 4.2.2.1 Weights and lengths 75
4.2.2.2 Tail, toe and scarring condition 79
vi
4.3 Discussion .......................................................................................................... 82
4.3.1 Habitat use 82 4.3.1.1 Considerations 84
4.3.2 General population morphometrics 86 4.3.2.1 Weights and lengths 86
4.3.2.2 Tail, toe and scarring condition 87
4.3.2.3 Considerations 90
4.3.3 Conclusions 92
5 REPRODUCTIVE BIOLOGY............................................................................ 93
5.1 Introduction....................................................................................................... 93
5.1.1 Objectives 95
5.2 Results ................................................................................................................ 96
5.3 Discussion ........................................................................................................ 102
5.3.1 Considerations 107
5.3.2 Conclusions 108
6 INTERSPECIFIC INTERACTIONS ............................................................... 109
6.1 Introduction..................................................................................................... 109
6.1.1 Objectives 111
6.2 Results .............................................................................................................. 112
6.2.1 Behavioural observations 112 6.2.1.1 Comparing focal animals in single and mixed species treatments 112
6.2.1.2 Comparing behavioural scans in single and mixed species treatments 118
6.2.2 Body condition measurements 120
6.3 Discussion ........................................................................................................ 122
6.3.1 Behavioural observations 122 6.3.1.1 Considerations 125
6.3.2 Body condition measurements 127 6.3.2.1 Considerations 128
6.3.3 Conclusions 130
7 GENERAL DISCUSSION ................................................................................. 131
8 APPENDICES..................................................................................................... 134
9 REFERENCES.................................................................................................... 142
vii
Table of figures
Figure 1.1 Australian range of rainbow skinks................................................................. 7
Figure 1.2 Hawaiian range of rainbow skinks .................................................................. 8
Figure 1.3 New Zealand range of rainbow skinks ............................................................ 8
Figure 1.4 New Zealand range of copper skinks ............................................................ 15
Figure 2.1 Equation for estimation of required sample size ........................................... 29
Figure 2.2 Location of study sites outside of the Auckland region ................................ 47
Figure 2.3 Location of Auckland region study sites....................................................... 48
Figure 3.1 Map showing Australian rainbow skink distribution records compiled........ 52
Figure 3.2 Predicted rainbow skink distribution based on Australian records ............... 53
Figure 3.3 Predicted rainbow skink distribution based on New Zealand records .......... 54
Figure 3.4 Predicted rainbow skink distribution based on Australian and New Zealand
records..................................................................................................................... 55
Figure 4.1 Weights of adult rainbow skinks ................................................................... 76
Figure 4.2 SVLs of adult rainbow skinks ....................................................................... 76
Figure 4.3 Total lengths of adult rainbow skinks ........................................................... 77
Figure 4.4 Weights of sub-adult rainbow skinks ............................................................ 77
Figure 4.5 SVLs of sub-adult rainbow skinks ................................................................ 78
Figure 4.6 Weights of juvenile rainbow skinks .............................................................. 78
Figure 4.7 SVLs of juvenile rainbow skinks .................................................................. 79
Figure 4.8 Probability of tail regeneration for rainbow skinks....................................... 81
Figure 4.9 Probability of toe loss for rainbow skinks..................................................... 81
Figure 4.10 Probability of scarring for male and female adult rainbow skinks.............. 82
Figure 5.1 Corrected mean testis volume by month ....................................................... 98
Figure 5.2 Corrected mean ovary volume by month ...................................................... 98
Figure 5.3 Mean follicle diameter by month ................................................................ 100
Figure 5.4 Percentage of each clutch size..................................................................... 101
Figure 5.5 Relationship between SVL and clutch size ................................................. 101
Figure 6.1 Mean percentage time spent in behavioural states per hour ....................... 113
Figure 6.2 Mean time spent basking, foraging or hidden by focal animals.................. 115
Figure 6.3 Mean duration of focal animals basking, foraging and hidden behaviours. 116
Figure 6.4 Mean frequency of tongue flick events by focal animals ........................... 117
Figure 6.5 Percentage of individuals in each treatment observed basking, foraging or
hidden during scan observations plotted against hours from “sunrise”................ 119
Figure 6.6 Mean body condition of animals in each treatment throughout the
interspecific interaction experiment...................................................................... 121
viii
Table of plates
Plate 1.1 Rainbow skink (Lampropholis delicata) ........................................................... 7
Plate 1.2 Copper skink (Cyclodina aenea) ..................................................................... 15
Plate 2.1 Live capture, weighing and SVL measurement methods ................................ 20
Plate 2.2 Ventral surface of rainbow skink indicating scar ............................................ 21
Plate 2.3 Examples of habitat categories ........................................................................ 27
Plate 2.4 Ventral dissections of adult male and female rainbow skinks......................... 32
Plate 2.5 Interior view of one enclosure used for housing skinks .................................. 35
Table of tables
Table 1.1 Comparison of rainbow and copper skink traits ............................................... 5
Table 1.2 Reported sightings of rainbow skinks that list habitat information................ 10
Table 1.3 SVLs recorded for Australian rainbow skink populations. ............................ 11
Table 2.1 Description of habitat categories .................................................................... 25
Table 2.2 Description of microhabitat categories ........................................................... 25
Table 2.3 Behaviour categories used for behavioural observations ............................... 37
Table 2.4 Observation session times............................................................................... 38
Table 3.1 Climate profile of rainbow skinks based on Australian records..................... 56
Table 3.2 Climate profile of rainbow skinks based on New Zealand records ................ 56
Table 3.3 Climate profile of rainbow skinks based on New Zealand and Australian
records..................................................................................................................... 56
Table 3.4 Presence/absence of rainbow skinks at sites surveyed ................................... 57
Table 4.1 Percentage of rainbow skinks occupying each substrate and refuge category
................................................................................................................................ 73
Table 5.1 Sex ratios of each rainbow skink population considered................................ 96
Table 5.2 Position of reproductive organs in dissected rainbow skinks......................... 96
Table 5.3 Details of rainbow skink nests encountered during fieldwork ..................... 102
ix
Abstract
Rainbow skinks (Lampropholis delicata) are the only introduced reptile that has
successfully established outside of captivity in New Zealand. They have been present in
this country since an accidental introduction from Australia in the early 1960s, and are
currently well established in several regions of the North Island. To date little, if any,
ecological research has been conducted on them in New Zealand, and there is no
indication of how they may be impacting on native fauna. Bioclimatic modelling based
on current distribution suggests great potential for continued spread of this species
inland and much further south of their currently known range. Rainbow skink dispersion
is facilitated by human activity, and they are hardy enough to survive human
disturbance in transit and in their habitat; care is advised when transporting materials to
areas of high conservation interest where rainbow skinks are not desired. Habitat use of
rainbow skinks in New Zealand encompasses a wide range of habitats and general
microhabitat use is also diverse and highly opportunistic. They occur sympatrically with
native New Zealand copper skinks (Cyclodina aenea) and exhibit common microhabitat
use. Rainbow skinks have a higher mean annual reproductive output than copper skinks.
Morphological measurements and reproductive biology of New Zealand rainbow skinks
are comparable to the majority of records for Australian and Hawaiian populations.
Percentages of rainbow skink tail and toe loss are similar to those recorded for native
New Zealand lizard populations and Australian rainbow skink populations. Captive
observations of rainbow and copper skinks did not reveal direct interaction or spatial
avoidance between these species. Despite an observed overlap of foraging time and
strategy, and prey size and type, mean body condition of rainbow and copper skinks
housed together did not differ significantly from control treatments. This research has
begun to clarify the ecology of rainbow skinks in New Zealand and has raised many
questions especially considering the potential for competition between rainbow and
native skinks. There is much scope for future research on rainbow skinks in New
Zealand.
1
1 General introduction
1.1 Invasive species
Identification of potentially invasive species is an area of great scientific interest (Mack
et al., 2000; Kolar & Lodge, 2001) as they can have serious negative effects on the
physical and biotic environment. For example wild pigs (Sus scrofa) in New Zealand
damage both native vegetation and soil in addition to predating native animal species
such as frogs and lizards (Ogle, 1981; Newman & Towns, 1985). The term “invasive
species” may be defined as: “an alien species which becomes established in natural or
semi-natural ecosystems or habitat, is an agent of change, and threatens native
biological diversity” (ISSG, 2000). In New Zealand, wild pigs and feral goats (Capra
hircus) may cause the decline of areas of native forest to the extent that local extinctions
of vulnerable species of native lizards occur (Ogle, 1981; Newman & Towns, 1985).
Invasive species, such as the red imported fire ant (Solenopsis invicta), may also
threaten human health and lifestyle (Jemal & Hugh-Jones, 1993; Kolar & Lodge, 2001).
Very few organisms potentially introduced into a new environment survive the
transportation phase (Mack et al., 2000; Kolar & Lodge, 2001; Leung et al., 2002), for
example many propagules in ballast tanks perish in transit (Mack et al., 2000). Should
immigrants survive movement to a new area, they are unlikely to colonise and
reproduce once they reach their destination (Mack et al., 2000), due to general resource
requirements and possible exclusion by competition or predation by resident species
(Losos et al., 1993; Losos & Spiller, 1999). Characteristics that enhance survival during
a transportation phase may not be an advantage for colonisation, e.g. a fish adapted to
nocturnal feeding may survive transport in a ballast tank but not in a new environment
that has clear waters or many competing nocturnal fish (Kolar & Lodge, 2001). Due to
this, local extinctions of introduced species often occur (Williamson & Brown, 1986;
Mack et al., 2000). Among those species that naturalise in their new range, only a few
become invasive (Mack et al., 2000; Kolar & Lodge, 2001; Leung et al., 2002).
2
In spite of the low probability of any given species becoming invasive, those species
that do have been identified as key factors in biodiversity loss for developed countries
(Craig et al., 2000; Mack et al., 2000; Kolar & Lodge, 2001), and may threaten native
species in a variety of ways (Mack et al., 2000). Threats to native species may include
predation, herbivory, habitat alteration, hybridisation, vectoring of disease or
competition (Mack et al., 2000). The accidental introduction of the brown tree snake
(Boiga irregularis) to Guam has devastated bird populations through predation, and has
practically eradicated all species of forest bird (Savidge, 1987). In New Zealand the
foraging of feral pigs (Sus scrofa) destroys litter layer structure and vegetation in native
bush (Ogle, 1981) altering the habitat to point that specialist native species (e.g.
Hochstetter’s frog (Leiolopelma hochstetteri)) can no longer inhabit these areas
(Newman & Towns, 1985; DSIR, 1987). When an introduced species is closely related
to a native species it may be possible for hybridisation to occur (Mack et al., 2000). For
example, in Great Britain Sitka deer (Cervus nippon) introduced from Japan have
hybridised with the native reed deer (C. elephaus) (Mooney & Cleland, 2001). In New
Zealand hybridisation of the native gray duck (Anas superciliosa) with the introduced
Hawaiian duck (A. wyvilliana) has occurred to the extent that gray duck are at risk of
becoming extinct as a discrete species (Rhymer & Simberloff, 1996). Avian malaria is
carried by the mosquito Culex quinquefasciatus that has been present in the Hawaiian
Islands since 1826 without significant impact (Mack et al., 2000). However, upon
introduction of the avian malaria parasite (Plasmodium relictum capistranoae) and
various species of Eurasian birds, many native Hawaiian bird species have become
extinct, or have been excluded from lowland areas due to their susceptibility to avian
malaria, which is prevalent among lowland bird populations (van Riper et al., 1986).
It is through competition that rainbow skinks (Lampropholis delicata) would be
expected to have the greatest impact upon the lizard fauna of New Zealand. In general
competition is more concentrated within species; however, individuals of different
species that have similar ecological requirements may also compete for resources
(Krebs & Davies, 1999). It has been suggested that interspecific competition plays a
role in the distribution of Anolis lizard species throughout the Bahamas (Losos &
Spiller, 1999). Upon investigation of sympatric and allopatric populations of Anolis
carolinensis and A. sagrei, Losos & Spiller (1999) found that populations of A.
3
carolinensis exhibited lower densities, and were at risk of extinction where they
occurred in sympatry with A. sagrei.
Previous introductions to New Zealand, for example the Australian brushtailed possum
(Trichosurus vulpecula), indicate that even the basic ecology of a species may change
markedly outside its native environment. In the example of the brushtailed possum their
population density is greatly increased in New Zealand, and can reach densities far
exceeding those found in their native country (Fitzgerald, 1984; Green, 1984), which
may indicate a greater amount of edible biomass available per area in New Zealand
(Green, 1984). Often escape from the native population checks such as predators,
parasites, competitors and host defences are suggested as reasons for such ecological
changes (Fitzgerald, 1984; Torchin et al., 2003), and the overall invasiveness of an
organism in a new environment (Jemal & Hugh-Jones, 1993).
Although numerous exotic lizard species have been reported in New Zealand the
rainbow skink is the only one to establish (Robb, 1974; West, 1979; Robb, 1986; Gill &
Whitaker, 2001; Gill et al., 2001). Therefore, it is pertinent to investigate the invasion
dynamics of rainbow skinks, especially as they are considered likely to spread beyond
their recorded distribution (West, 1979; Gill & Whitaker, 2001), and have been
demonstrated to be invasive in other countries. In the Hawaiian Islands moth skinks
(Lygosoma noctua noctua) appear to have been replaced by the rapidly expanding
populations of rainbow skinks (Hunsaker & Breese, 1967 recorded as Leiolopisma
metallicum; Baker, 1979).
All native New Zealand lizards are endemic, and species are highly diverse given the
temperate climate and area of New Zealand (Robb, 1974; Higham, 1995; Towns et al.,
2001). Native lizard species have undergone extinctions and drastic reductions in range
to the point that approximately half of the species previously found in the North Island
are currently restricted to offshore islands (Towns et al., 2001). In the past lizards have
been greatly impacted by habitat destruction, and more recently the introduction of
predators and competitors by humans (Dick, 1980a); presently, expanding urbanised
areas and invasive species continue to marginalise mainland species of lizard (Freeman,
4
1997; Towns et al., 2001). Therefore it is important to readdress the general ecology of
rainbow skinks within New Zealand, with special consideration of potential impacts on
native lizards.
Examination of interspecific interactions between rainbow and copper skinks
(Cyclodina aenea) were conducted as part of this research. Copper skinks were chosen
as they share many ecological and behavioural characteristics with rainbow skinks
(Table 1.1). Rainbow and copper skinks overlap widely in terms of geographic
distribution and habitat types; which indicates that they are likely to occur at the same
locations within their range. In addition both species are diurnal, which means that they
would be active at the same time. Both species are generalist feeders and due to similar
body sizes would be expected to prey on insects of approximately the same size,
suggesting potential dietary overlap. Taken together these factors indicated that copper
skinks were the logical choice for examining potential impacts of rainbow skinks on
New Zealand’s native lizard species.
5
Table 1.1 Comparison of selected traits of rainbow and copper skinks.
Characteristic Copper skink Rainbow skink
Status Endemic (Bell, 1986; Porter,
1987; Bell, 1996)
Introduced (Bell, 1986;
Greer, 1989)
Distribution Throughout the North Island
(Gill & Whitaker, 2001)
Auckland area, Coromandel
Peninsula, Tauranga, Te
Puke (Robb, 1986; Gill &
Whitaker, 2001; information
courtesy of Leigh Marshall,
New Zealand Department of
Conservation (DoC))
Habitat use Urban areas, forest, maritime
and supralittoral zones (Gill
& Whitaker, 2001)
Urban areas, forest,
farmland, scrub (Gill &
Whitaker, 2001)
Time of activity Diurnal† (Porter, 1982a,
1987; Bell, 1996; Gill &
Whitaker, 2001)
Diurnal* (Baker, 1979;
Ingram, 1990; Forsman &
Shine, 1995a)
Diet Invertebrate generalist
(Porter, 1987; Bell, 1996)
Invertebrate generalist
(Lunney et al., 1989)
SVL Up to 62 mm (Gill &
Whitaker, 2001)
Up to 55 mm (Gill &
Whitaker, 2001)
Oviparous/Viviparous Viviparous (Gill &
Whitaker, 2001)
Oviparous (Baker, 1979;
Ingram, 1990; Forsman &
Shine, 1995a)
Young present in
population
January to March (Melgren,
1981; Porter, 1987; Gill &
Whitaker, 2001)
February to March (Gill &
Whitaker, 2001)
† Meads (1971) records this species as nocturnal.
*Schulz & Eyre (1997) have also encountered rainbow skinks active nocturnally during favourable
weather conditions.
1.2 The rainbow skink (Lampropholis delicata)
(Squamata: Scincidae)
The rainbow skink (De Vis, 1888) (Plate 1.1) is a small, oviparous (egg laying) lizard,
which is largely considered to be diurnal (Baker, 1979; Shine, 1983; Ingram, 1990;
Forsman & Shine, 1995a), and has been suggested to have a short (two year) life span
under natural conditions (Hutchinson et al., 2001). Some controversy exists around the
species as it represents a number of different morphotypes (Ehmann, 1992), colour
6
patterns, and genotypes (Mather, 1986; Mather, 1990). They are generalist feeders,
predating on a wide range of invertebrates including amphipods, annelids, arachnids,
beetles, bugs, cockroaches, small crustaceans, flies, hymenopterans, isopods,
lepidopterans, and snails (Green, 1965; Rose, 1974; Baker, 1979; Crome, 1981; Shea,
1985; Lunney et al., 1989; Ehmann, 1992; pers. obs.).
1.2.1 Distribution
The rainbow skink is native to Australia where it inhabits a wide geographic range,
across 25° of latitude, from Cairns to Tasmania (Forsman & Shine, 1995a) (Figure 1.1).
The rainbow skink has been accidentally introduced to the Hawaiian Islands, New
Zealand (Greer, 1989; Ehmann, 1992; Hutchinson et al., 2001) and Lord Howe Island
(Whitaker, 2003b).
Introduced to the Hawaiian island of O’ahu in approximately 1917 (Oliver & Shaw,
1953 recorded as Lygosoma metallicum), rainbow skinks had dispersed to all major
inhabited islands in this group by 1978 (Baker, 1979) (Figure 1.2). Rainbow skinks
have also been accidentally introduced to Auckland, New Zealand in the 1960s,
probably via movement of cargo (Gill & Whitaker, 2001). They are known to be well
established in the greater Auckland area, Coromandel Peninsula, Tauranga, and Te
Puke; populations are also present in the Waikato region, and there have been recent
sightings in Wanganui, Whakatane (Table 1.2) and Whangarei (SRARNZ, 2003)
(Figure 1.3).
7
Plate 1.1 Rainbow skink (Lampropholis delicata). Photograph by the author.
Figure 1.1 Australian range of rainbow skinks indicated by shading (based on data from Swan (1990),
Cogger (2000) and Hutchinson et al. (2001); map modified from Geoexplorer (2002)). Map prepared with
assistance from P Barnett.
40°S
25°S
10°S
140°E
500 km
Sydney
Brisbane
Cairns
Hobart
Melbourne
8
Figure 1.2 Hawaiian range of rainbow skinks indicated by shading (based on data from Baker (1979);
map modified from Pike Street Industries (2002)). Map prepared with assistance from P Barnett.
Figure 1.3 New Zealand range of rainbow skinks indicated by shading (based on data from Table 1.2 &
SRARNZ 2003); map modified from Geoexplorer (2002)). Map prepared with assistance from P Barnett.
160°W
20°N
Auckland
50 km
37°S
175°E
40°S
Hawai’i
Kaho’olawe
Lana’i
Moloka’i
O’ahu Kaua’i
N’ihau
100 km
Honolulu
Maui
9
1.2.2 Habitat use and general population and morphological
parameters
Rainbow skinks utilise a wide variety of habitats in Australia, from supralittoral areas to
mountains, including forests, farms and suburban gardens (Green, 1965; Harris &
Johnston, 1977; Greer & Kluge, 1980; Ingram, 1990; Ehmann, 1992; Clerke & Alford,
1993; Kutt, 1993; Driessen & Brereton, 1998; Cogger, 2000; Hutchinson et al., 2001).
High levels of human disturbance (e.g. sand mining, logging) result in low-density
populations or an absence of this species (Lunney et al., 1991; Letnic & Fox, 1997;
Taylor & Fox, 2001a, b), although in general rainbow skinks are robust to human
activities (Quay, 1973 recorded as Lygosoma metallicum; Baker, 1979; pers. obs.).
Hawaiian populations also utilise a range of habitats, including gardens and rainforest,
roadsides, and areas surrounding crops (Quay, 1973; Baker, 1979). In addition rainbow
skinks have been found at the highest altitude recorded for any reptile in this state
(Baker, 1979). New Zealand specimens have been sighted in, or collected from urban
areas, farmland, scrub, and forest environments (information courtesy of Leigh
Marshall, New Zealand Department of Conservation (DoC)) (Table 1.2).
In New Zealand, rainbow skinks have been found in suburban gardens and industrial
sites, if adequate cover in the form of logs, stones or vegetation is available (Gill &
Whitaker, 2001). Microhabitat use in Australia takes the form of refuges such as stones,
vegetation litter and wood piles (McCoy & Busack, 1970 recorded as Leiolopisma
metallica; Shea, 1985; Graham, 1987) and similar microhabitat use has been recorded in
Hawaiian populations (Quay, 1973). Leaf litter density, patchiness of bare ground and
the height of canopy trees were found to positively influence the abundance of rainbow
skinks in Australian populations (Mather, 1986; Graham, 1987; Twigg & Fox, 1991;
Kutt, 1993; Taylor & Fox, 2001a, b). Microhabitat preference investigations carried out
by Howard et al. (2003) indicated that rainbow skinks had a preference for litter that
was mediated by patchiness of overall litter cover, structural characteristics of the litter
leaves and litter depth.
10
Table 1.2 Reported sightings of rainbow skinks as held by DoC that list habitat information (December
2003) (DoC) Amphibian and Reptile Database; information courtesy of Leigh Marshall).
Sight Date
Altitude
(m) District No. Seen Habitat
24-Oct-00 40-100 10 Broadleaf forest/Scrub
25-Sep-02 2 Northland 1 Urban
15-Jun-84 30 Auckland 5+ Bare rocks/Scrub
1-Dec-84 30 Auckland 1 Scrub/Bare rocks
19-Mar-94 100 Auckland 28 Scrub/Urban
14-Jan-96 Auckland 7 Scrub
1-Jan-97 Auckland 10 Urban
1-Jan-99 Auckland 20 Urban
3-Nov-99 100 Auckland 1 Urban
12-Jan-03 Auckland 1 Bare rocks
9-Apr-03 Bay of Plenty 1 Urban
19-Jul-83 35 Waikato 1 Urban
14-Mar-00 80 Waikato abundant Broadleaf forest/Scrub/Urban
14-Mar-00 10 Waikato Farmland
14-Mar-00 90 Waikato abundant Scrub/Farmland
3-Apr-02 Waikato 1 Scrub
12-Nov-03 Waikato 1 Urban
21-Feb-01 Wanganui 1 Urban
7-Feb-02 5 Wanganui 1 Urban
14-Apr-02 2 Wanganui 1 Urban
25-Jun-02 Otago 1 Urban
Gill & Whitaker (2001) record a maximum snout to vent length (SVL) of 55 mm for
adult rainbow skinks, and a range of SVLs have been recorded in Australian
populations (Table 1.3). In Hawaiian populations average adult female SVLs range
from 39 mm for Oah’u, 41 mm for Hawai’i and up to 42 mm for Kaua’i (Baker, 1979).
This species may be very abundant on a local scale within its native country (Forsman
& Shine, 1995a, b; Cogger, 2000), and may dominate lizard assemblages in numerical
terms (Mather, 1986; Taylor & Fox, 2001a, b). Similar densities have been found in the
Hawaiian populations (300-400 individuals within 100m2) (Baker, 1979), and
populations have been described as abundant and dense in this state (Quay, 1973).
However, Kutt (1993) found mean densities of 0.18 (±0.09 SE) per 500 m2 in thinned
and 0.3 (±0.18SE) per 500 m2 in unthinned Australian forest sites. Although no studies
11
regarding population densities of rainbow skinks have been undertaken in New Zealand
to date, there have been several verbal reports of communal nesting in this country,
suggesting high densities in some locations (pers. obs.).
Table 1.3 Snout to vent lengths (SVLs) recorded for Australian rainbow skink populations.
SVL (mm) Notes Reference
34 to 42 Adult female (Shine & Greer, 1991)
36 Males (Lunney et al., 1989)
37 Females (Lunney et al., 1989)
37 (Harris & Johnston, 1977)
37 Overall mean for populations
considered
(Mather, 1986)
38 (Downes & Hoefer, 2004)
40 (Twigg & Fox, 1991; Forsman &
Shine, 1995a, b; Cogger, 2000;
Thompson et al., 2001)
41 (Clarke, 1965)
42 (Ehmann, 1992)
45 (Shine, 1983)
47 Tasmania (Hutchinson et al., 2001)
50 Victoria (Hutchinson et al., 2001)
1.2.3 Reproductive biology
The reproductive biology of rainbow skinks is primarily described based on overseas
studies. Ovulation begins in spring for mature female rainbow skinks in New South
Wales populations, with spermatogenesis in males beginning in early spring (Shine,
1983; Joss & Minard, 1985). The eggs are held for 40-60 days with oviposition into
moist sites, such as under fallen logs and stones, occurring in summer (Green, 1965;
Shine, 1983). Eggs are laid into refuges, and nests may be communal between species
and individuals with up to 250 eggs recorded (Clarke, 1965; Green, 1965; Shine, 1983;
Ehmann, 1992; Couper & Schneider, 1995).
Mean clutch sizes of 2.7 to 4.4 eggs have been recorded, with clutch size ranges of one
to eight eggs, and differ markedly between Australian populations (Green, 1965; Joss &
12
Minard, 1985; Shine & Greer, 1991; Clerke & Alford, 1993; Forsman & Shine, 1995a,
b; Thompson et al., 2001). Clutch size in the Hawaiian Islands also exhibits disparity,
with means of 3.5 eggs (±1.8) for O’ahu populations, to 4.7 eggs (±1.3) for Hawai’i
populations, and ranges of one to five and three to seven eggs respectively (Baker,
1979). The reason proposed for this was the significantly smaller body size of O’ahu
females limiting the size of their body cavity, and therefore the number of eggs
produced (Baker, 1979). The idea of body cavity volume constraining clutch mass has
been investigated in more detail for other species and evidence supporting this concept
presented for snake and lizard species (Shine & Greer, 1991; Shine, 1992; Forsman &
Shine, 1995b).
Eggs of rainbow skinks hatch in February and March (Gill & Whitaker, 2001), with
neonates of ranging from 17-19 mm (Clarke, 1965; Graham, 1987). Females in Sydney,
Australia populations have been reported to produce one clutch per year (Joss &
Minard, 1985); however, Ehmann (1992) reported up to three clutches per year in
Sydney populations. Shine (1983) has suggested a latitudinal gradient in clutch
frequency in this species with fewer clutches produced in southern populations.
1.2.4 Interspecific interactions with lizards
Investigation of an Australian lizard assemblage, containing rainbow skinks, by Twigg
& Fox (1991) found minimal data to support direct competition as a structuring factor.
However, it has been suggested that the smaller body size of individuals in the
Hawaiian populations on O’ahu were the result of high population densities, and the
presence of other skink species on this island, producing both intraspecific and
interspecific competition for space and prey (Baker, 1979). It has also been suggested
that the increased range of rainbow skinks in the Hawaiian Islands has resulted in the
displacement of moth skinks (Hunsaker & Breese, 1967; Baker, 1979). In New Zealand
captive rainbow skinks have been observed to successfully compete for food with native
13
copper skinks (West, 1979). Apart from this record of captive skink observations no
other information regarding rainbow skink interactions with native species was found.
1.3 The copper skink (Cyclodina aenea)
(Squamata: Scincidae)
Copper skinks (Girard, 1857) (Plate 1.2) are New Zealand’s smallest native lizard
(Melgren, 1981; Gill & Whitaker, 2001; Green, 2001), and are viviparous (live bearing),
as are all but one of the native lizards (Robb, 1974; Bell et al., 1983; Robb, 1986; Cree,
1994; Higham, 1995; Gill & Whitaker, 2001). In captivity copper skinks may live for
eight to ten years (Meads, 1971), however a life span of four to five years is probably
more realistic for wild individuals (Porter, 1982a). They are diurnally active, and feed
on a range of invertebrates including amphipods, arachnids, beetles, flies,
hymenopterans and isopods (Barwick, 1959; Porter, 1982a, 1987; Bell, 1996; Gill &
Whitaker, 2001).
1.3.1 Distribution
Copper skinks occur throughout the North Island of New Zealand and associated
offshore islands in widespread discrete populations (Hardy, 1977; Dick, 1980a; Dick,
1980b; Melgren, 1981; Towns et al., 1985; Gill & Whitaker, 2001) (Figure 1.4).
14
1.3.2 Habitat use and general population and morphological
parameters
Copper skinks occupy environments such as forest, urban areas (including gardens)
where adequate ground cover is present, and the maritime and supralittoral zones (Dick,
1980b; Melgren, 1981; Porter, 1982a, 1987; Bell, 1996; Gill & Whitaker, 2001;
Habgood, 2003). In Auckland gardens and some Wellington suburbs they are a common
lizard species (Porter, 1982a, 1987; Gill & Whitaker, 2001). Microhabitats utilised
include refuges such as rocks, leaf litter, rotten logs and dense vegetation (Meads, 1971;
Melgren, 1981; Porter, 1982a); even earthworm burrows (Porter, 1982b).
The copper skink has a SVL of up to 62 mm (Gill & Whitaker, 2001), with the majority
of individuals examined by Porter (1982a) measuring between 51-62 mm SVL, and
Habgood (2003) finding individuals ranging from 24-64 mm SVL. Porter (1982a) found
the mean SVL of immature copper skinks to be 29 mm, and the smallest captured was
21 mm SVL. Population estimates of 100-170 individuals have been reported for a
population inhabiting One Tree Hill, Auckland (Porter, 1987) and a maximum of 287
for a Tiritiri Matangi Island population (New Zealand) (Habgood, 2003).
15
Plate 1.2 Copper skink (Cyclodina aenea) (Gill & Whitaker, 2001:58).
Figure 1.4 New Zealand range of copper skinks indicated by shading (based on information from Pickard
& Towns (1988); map modified from Geoexplorer (2002)).
37°S
175°E
40°S
Auckland
50 km
16
1.3.3 Reproductive biology
Mating has been recorded from September to November, with gravid females found in
Auckland populations from November to February, and young are born from January to
March (Melgren, 1981; Porter, 1982a, 1987; Gill & Whitaker, 2001). The young of the
season were observed in an Auckland population from late January to late February by
Porter (1987). Captive copper skinks have been recorded to give birth to three young
(Anonymous, 1980), with ranges of one to seven and two to five recorded by Melgren
(1981) and Meads (1971) respectively. Annual reproductive output for wild populations
has been calculated at two offspring per female per year (Barwick, 1959). This is close
to the mean of 2.26 offspring (SE: 0.1) found by Habgood (2003), who recorded a range
of two to three offspring for the populations of copper skink investigated on Tiritiri
Matangi Island.
1.3.4 Interspecific interactions with lizards
Research conducted by Porter (1987) and Habgood (2003) showed that the ecological
niche of copper skinks overlapped widely with ornate (Cyclodina ornata), and moko
skinks (Oligosoma moco) respectively. Porter (1987) suggested that copper and ornate
skinks may not be able to coexist over long periods of time and found evidence of
ornate skinks exhibiting a competitive advantage over copper skinks within habitats
where the two species co-occurred in Auckland populations. The larger size of ornate
skinks was suggested as the reason for their advantage (Porter, 1987); however, escape
behaviours observed for copper and ornate skinks indicated that copper skinks may
have been able to expand their range as the environment was modified by humans and
mammalian predators were introduced (Porter, 1987). In contrast, Habgood (2003) did
not find evidence of competition resulting in an incumbent advantage between copper
and moko skinks investigated on Tiritiri Matangi Island.
17
1.4 Research objective
The main objective of this research is to clarify the potential of rainbow skinks to
become an invasive species in New Zealand. To investigate this potential the current
and predicted distribution, habitat use, general morphological measurements,
reproductive and behavioural ecology of rainbow skinks were examined.
1.5 Thesis plan
Each aspect of the research will be considered in the following manner:
Chapter One introduces selected background concepts pertaining to invasive species
and reviews the literature concerning rainbow and copper skinks.
Chapter Two details the methods and the study sites used in this research.
Chapter Three addresses the current and predicted distribution of rainbow skinks in
New Zealand.
Chapter Four indicates general trends of habitat and microhabitat use, in addition to
considering morphological features of selected Auckland populations of rainbow
skinks. Comparison with Australian and Hawaiian data for rainbow skinks, or native
New Zealand lizard populations, is carried out as appropriate.
Chapter Five outlines the reproductive cycle for selected Auckland populations of
rainbow skinks, in addition to considering sex ratios and rainbow skink nests
encountered. Comparison with reproductive data for rainbow skinks from Australian
and Hawaiian populations is carried out.
Chapter Six investigates the behaviour and body condition of captive rainbow and
native New Zealand copper skinks.
Chapter Seven summarises the conclusions of this research.
18
2 Methods
2.1 Introduction
Methods common to several areas of the research are detailed in Section 2.2 to
minimise repetition in the subsequent sections. Research was conducted with approval
from The University of Auckland Animal Ethics Committee (permit 10/R79), and the
New Zealand Department of Conservation (DoC) (permit WK-14028-FAU and
AK/12661/RES).
2.2 General methods
2.2.1 Environmental data
Climate data were recorded using Hobo dataloggers (model no. HO-08-004-02), Zeal
wet and dry bulb hygrometers (Mason’s type), and Brannan maximum-minimum
thermometers. For visited sites latitude, longitude and elevation data were recorded
using a Global Positioning Device Garmin etrex (12 channel GPS).
2.2.2 Capture and handling of skinks
Capture and handling of all skinks followed standard techniques used by DoC and
experienced reptile biologists. Animals were collected by hand searches and live
19
trapping using skink refuges. Skink refuges consisted of Black Trakka tunnels, from
which skinks could freely enter and exit, filled with foliage, and wired down for
stability (Plate 2.1 A). Release of all freed animals was at their point of capture. Lizards
were identified to species level using the New Zealand Frogs & Reptiles fieldguide by
Gill & Whitaker (2001). Rainbow skinks (Lampropholis delicata) were noted as
juvenile, sub-adult or adult according to the methods of Joss & Minard (1985).
Weight was measured to the nearest 0.01g using Ohaus SC2020 electronic field scales;
when wet weather prohibited the use of Ohaus scales, 5g and 10g Pesola spring loaded
balances were used and weight was calculated to the nearest 0.1g. Measurements of live
skinks were taken with the animal held in a plastic ziplock bag (Plate 2.1 B); the
animals’ weight was then determined by weighing the bag and subtracting bag weight
from skink and bag weight. Dead skinks were measured by placing the animal directly
onto the Ohaus scales.
Snout to vent length (SVL) and tail length (TL) were measured to the nearest millimetre
using a 30 cm ruler. SVL is a measurement from the tip of the nose to the cloacal
opening; TL is a measurement from the cloacal opening to the tip of the tail (in the case
of a forked tail the longest tail length was used). Length of regenerating tail portions
was also noted by measuring from the cloacal opening to the start of the regenerating
tissue. Measurements of live skinks were taken while the animal was held in a plastic
ziplock bag (Plate 2.1 C); measurements of dead skinks were taken with the animal
placed flat on a bench.
The number of toes fully or partially lost was recorded, and state of tail regeneration
was noted as entire, regenerating or lost (tail broken with no regeneration). The sex of
sub-adults or adults (animals over 30 mm SVL (Joss & Minard, 1985)), was ascertained
by attempting to evert the hemipenes; failure to do was taken to indicate a female. The
presence, number and position of any scarring (Plate 2.2) was also recorded.
20
A)
B) C)
Plate 2.1 A) Modified Black Trakka tunnel used as a skink refuge. B) Illustration of weighing method
used. Rainbow skink in ziplock bag weighed using Ohaus scales. C) Illustration of SVL measurement.
Rainbow skink in ziplock bag measured using 30cm ruler. Photograph A by the author, photographs B &
C courtesy of J. Guilbert.
21
Plate 2.2 Ventral surface of rainbow skink with arrow indicating scar. Photograph courtesy of I.
McDonald.
2.2.3 Data analysis
When data were available for multiple samples, normality distribution (Shapiro-Wilk W
test) and homogeneity of variance (Brown & Forsythe's test) tests were initially carried
out to identify further appropriate statistical tests. All analyses were conducted using
STATISTICA version 6 (StatSoft, 2001) and SAS version 6.12 (SAS Institute, 1989-
1996), and tested for statistical significance to p < 0.05.
22
2.3 Current and predicted distribution methods
The Bioclimatic Prediction System computer programme (BIOCLIM) (Nix, 1986;
Busby, 1991) was used to map the potential distribution of rainbow skinks based on
microclimate (500 x 500 m) temperature and rainfall data from throughout New
Zealand. New Zealand climate data were sourced from the national Meteorological
Service network of recording stations and climate surfaces created based on the
methods of Mitchell (1991). Daily maximum and minimum temperatures and mean
monthly rainfall for the Australian states of New South Wales, Victoria, South Australia
and Tasmania were gathered from the Commonwealth Bureau of Meteorology website
(CoA, 2004).
Predicted distribution maps were constructed using records of rainbow skinks from
Australia and New Zealand. These records were sourced from museums, published
accounts, the DoC database, Ministry of Agriculture and Forestry records, consultation
with Tony Whitaker, members of the New Zealand Herpetological Society and DoC
staff in addition to personal observation (Appendix I). Records consisted of latitude,
longitude and elevation data. Missing data was calculated from topographical maps
NZMS 260 (DSLI, 1996), Fullard et al. (1983) or the internet resource Falling Rain
Genomics (2004). It was assumed that records were correctly identified, that the
latitude, longitude and elevation data given was accurate and records indicated
conditions suitable for rainbow skink establishment.
Maps of predicted rainbow skink distribution in New Zealand show where the climate
lies within the climate profile calculated from the records, i.e. if all 18 variables (see
Section 2.3.2) were within the climate profile the location was recorded as suitable.
Maps were created of the Australian distribution of rainbow skinks based on 313
Australian records; predicted New Zealand distribution based on 145 Australian
records, predicted New Zealand distribution based on 61 New Zealand records, and
predicted New Zealand distribution based on combined Australian and New Zealand
23
records. Only 145 Australian records were used to estimate predicted New Zealand
distribution due to the lack of climate data for Queensland and the Northern Territory,
and duplicate records.
2.3.1 Survey methods
One off surveys to ascertain presence or absence of rainbow skinks were conducted at
34 sites (sites A to E, I, J, and N to X; see Section 2.7, Figures 2.2 & 2.3 for brief site
descriptions and locations). Note that the Auckland sites of Tapapakanga Regional Park,
Regional Botanic Gardens, Omana Regional Park, and Awhitu Regional Park were not
surveyed by the author but by Dr Graham Ussher (Natural Heritage Scientist for the
Auckland Regional Council). The cities surveyed were chosen as they represent regions
where rainbow skinks have been recorded, or because they are possible destinations for
rainbow skink eggs through various transport mechanisms e.g. in potting mix from
nurseries. Latitude, longitude, elevation, search time (in person hours) and search area
was recorded for each site. To describe the weather conditions experienced during the
survey maximum and minimum temperature and relative humidity were noted.
Presence or absence of rainbow skinks at each site was ascertained by hand searching
the site and identifying captured lizards. Habitats in which rainbow skinks had been
most frequently observed during other fieldwork (human-modified, rank vegetation and
scrubland (Table 2.1)), were selected during the survey to maximise the possibility of
detection. A maximum of three rainbow skinks from each site had detailed photographs
taken to allow independent species identification confirmation. The fieldwork for this
section took place between December 2003 and January 2004.
24
2.3.2 Data Analysis
Climate profiles for rainbow skinks consist of: annual mean, highest and lowest
monthly mean, range, seasonality (range/annual mean (Mitchell, 1991)), and wettest,
driest, coldest and warmest quarter measurements for minimum and maximum
temperature and rainfall. These were calculated based on climate variables estimated for
sites with rainbow skink records from Australia, New Zealand, and both countries
combined. The percentage of sites surveyed for the present study that had rainbow
skinks present was calculated.
2.4 Population parameters and habitat use methods
2.4.1 Habitat use
Investigation of habitat and microhabitat use by rainbow skinks was carried out at nine
sites where rainbow skinks were observed during hand searches (sites D, F to H, K, M,
R, and U; see Section 2.7, Figure 2.2 & 2.3 for brief site descriptions and locations).
Habitats present at each site were broadly categorised into human modified (Plate 2.3
A), rank vegetation (Plate 2.3 B) and scrubland (Plate 2.3 C) (Table 2.1), and used to
determine general rainbow skink habitat use. These habitat types were chosen as they
were easily identifiable as discrete habitats. Upon capture of a rainbow skink the habitat
and a description of the microhabitat utilised was recorded (Table 2.2). Microhabitat
description included the height of canopy or other form of cover above the skink, the
type of substrate they were on, and any refuge utilised. The occurrence of other lizard
species utilising the habitats searched was also noted. Fieldwork for this section of the
study took place between February and December 2003.
25
Table 2.1 Description of habitat categories.
Category
(abbreviation)
Description
Human-modified
(HM) (Plate 2.3 A)
Occurring within or directly outside (< 1m) buildings, or areas
which are under a frequent human disturbance regime, e.g.
camping areas.
Rank vegetation
(RV) (Plate 2.3 B)
Vegetation not regularly disturbed by humans or human instigated
activities (does not include utilised pasture or lawn)
Scrubland
(S) (Plate 2.3 C)
Vegetated with plant species that have not achieved complete
canopy closure, e.g. revegetated areas
Table 2.2 Description of microhabitat types.
Category Substrate type
Artificial Artificial compounds: cardboard, fibrolite, fabric, glass, metal,
newspaper, plastic (including skink refuges), shade cloth, and weed
mat
Concrete Laid concrete and concrete slabs
Gravel/rock Gravel and rock
Growing media Potting mix and sand
Soil Soil
Litter/vegetation Leaf litter and vegetation
Wood Standing dead trees, fallen logs, lumber and bark
Category Refuge type
Artificial As above with the addition of canvas, corrugated iron, freight
container and polystyrene
Concrete As above
Gravel/rock As above
Soil As above
Litter/vegetation As above
Wood As above
26
A)
B)
27
C)
Plate 2.3 Examples of habitat categories. A) Human modified. B) Rank vegetation. C) Scrublands.
Photographs by the author.
2.4.1.1 Data analysis
Overall utilisation of refuges and canopy cover was calculated as a percentage. For sites
where more than ten individuals were observed, use of microhabitat type was expressed
as a percentage. Where over ten individuals of the site sample had been sexed
differences in microhabitat use between male and female rainbow skinks were
compared using a Chi-square test for homogeneity.
28
2.4.2 General morphological features
Information on general morphological features (see Section 2.2.2) of six rainbow skink
populations were collected (sites D, F to H, K and M see Section 2.7, Figure 2.2 & 2.3
for brief site descriptions and locations). The fieldwork for this section took place
between February and November 2003.
2.4.2.1 Data analysis
Box plots showing weight, SVL and total length of adult, sub-adult and juvenile
rainbow skinks were plotted for samples of over ten animals. A Kruskal-Wallis
ANOVA was used to compare weights and SVLs of adults and juveniles. Total length
of adult rainbow skinks was compared using a t-test for unequal sample sizes. Weights
and SVLs of sub-adult rainbow skinks were compared using a Mann-Whitney U-test.
Tail length as a percentage of SVL was calculated from adult rainbow skinks with entire
tails; samples were pooled for this calculation as SVLs and tail lengths were not
significantly different between samples.
The percentage of all rainbow skinks assessed for tail and toe condition (see Section
2.2.2) was calculated. Differences in tail, toe and scarring condition between
populations, life stages and sexes were analysed using categorical data analysis
(maximum likelihood ANOVA) (SAS Institute, 1989-1996). Analysis of associations
between tail and toe loss and occurrence of scarring was carried out using Chi-square
tests of association.
29
2.5 Reproductive biology methods
A maximum of 20 mature adult rainbow skinks (over 35 mm SVL (Clarke, 1965; Joss
& Minard, 1985)), were removed from three sites (F, H and M, see Section 2.7, Figure
2.2 & 2.3 for brief site descriptions and locations) every month from February to April
and September to November 2003 (Appendix II). Sometimes the number taken was
under 20 per month as searching was stopped at each site, regardless of number
collected, after five days. The timeline of this section was chosen to cover the beginning
and end of the reported Australian breeding season (Joss & Minard, 1985; Clerke &
Alford, 1993; Forsman & Shine, 1995b) to investigate whether evidence of an extended
or reduced breeding season existed. Twenty animals were removed per site per month,
as this was a practical minimum number based on the consideration of possible
population impacts; all populations were much larger than 20 individuals. In addition, to
achieve a statistical power of 0.8 in detecting a difference between populations, a
sample of 20 had to be taken (Figure 2.1).
( )432
2)20(2
××=φ
24
80=
= 1.83
This result (1.83) estimates a power of ~0.80. Therefore, a sample size of 20 was
required.
Figure 2.1 Equation for estimation of required sample size (Zar, 1996).
Upon capture the weight, SVL, TL, and tail, toe and scarring condition of skinks was
recorded (see Section 2.2.2). Animals removed were killed by freezing following the
methods of Mather & Hughes (1992), and recommendations by Karns (1986); after
freezing, they were placed in 70% ethanol solution (Karns, 1986). Dissections were
30
carried out after storage for a maximum of seven months. Dissection of all specimens
collected was not possible due to time constraints, however a minimum of ten
dissections (five male and five female where possible) were performed for each sample
per month per site. Dissections were carried out under a dissecting microscope (Nikon
model: SMZ-2B; x10 magnification). Sex, position of reproductive organs, general
appearance of the oviduct, presence of yolked ovarian follicles and number of oviducal
eggs and follicles were recorded (Plate 2.4). Maximum and minimum diameters of
testes, ovaries and shelled eggs were taken (Plate 2.4 B, C & D) to calculate the volume
the formula for an ellipsoid was used: 4/3πab2 (a = half maximum diameter; b = half
minimum diameter) (Mayhew, 1963; Wapstra & Swain, 2001). The diameter of ovarian
follicles larger than 1 mm was measured. All measurements were taken to the nearest
0.25 mm using Castroviejo callipers.
The number of eggs, status of eggs, hatched (determined by the presence of empty
eggshells) or unhatched, description of microhabitat and date of observation of rainbow
skink nests observed during fieldwork was recorded (sites G, H, M and U, see Section
2.7, Figure 2.2 & 2.3 for brief site descriptions and locations). The presence of juveniles
in rainbow skink populations was also noted.
2.5.1 Data analysis
Sex ratios were compared to a 1:1 (male:female) ratio using Chi-square analysis, and
comparison between life stages and populations was carried out using categorical data
analysis (maximum likelihood ANOVA) (SASInstitute, 1989-1996). Mean testis and
ovary volumes were calculated by averaging the volume of organs found in each
individual to give a single result for each specimen (Simbotwe, 1985). These
measurements were then corrected for body size by multiplying the mean volume of
testes or ovaries by 100 and then dividing by the SVL of the individual (Habgood,
2003).
31
A)
B)
32
C)
D)
Plate 2.4 Photographs of ventral dissections of adult male and female rainbow skinks. A) Female left
side: white arrow indicates fleshy oviduct; black arrow indicates ovary filled with enlarged ova. B)
Female: black arrow indicates one of three oviducal eggs in the left oviduct; white arrow indicates right
ovary. C) Male right side: maximum and minimum diameters of the testis are indicated. D) Female left
side: maximum and minimum diameters of the ovary are indicated; white arrow indicates normal oviduct;
note yolked ovarian follicles in ovary. All photographs courtesy of I. McDonald.
Min
Max
Min
Max
33
Comparison of corrected mean testes volumes between populations were made using a
Kruskal-Wallis ANOVA, and comparison of the corrected mean volumes of ovaries
between populations were made for February using a Mann-Whitney U-test (females
were only captured from two sites during the February sample) and for March, April,
September, October and November using a Kruskal-Wallis ANOVA. As samples from
each population were not significantly different they were pooled for graphing and
consideration of between month differences. Box plots were created for pooled
corrected mean volumes of testes and ovaries for each month sampled. Corrected mean
volumes for testes and ovaries were compared between months using a Kruskal-Wallis
ANOVA.
As the corrected mean volume of ovaries was not found to be significantly different
between sites; all samples were pooled for consideration of follicle diameter, and a
mean diameter calculated per individual. Mean egg volume was calculated for each
clutch of oviducal eggs observed and compared between clutches using a Kruskal-
Wallis ANOVA. As no significant differences were found, the mean number of eggs per
clutch and mean egg volume was calculated from the pooled values of all clutches and
oviducal eggs. Clutch sizes were compared using a Kruskal-Wallis ANOVA, and as no
significant difference in clutch size was found, all clutches were pooled for examination
of the percentage of clutches of each size and the relationship between SVL and clutch
size, which was assessed using a Spearman’s rank correlation.
2.6 Interspecific interaction methods
Sixty-three adult skinks: 13 adult copper (Cyclodina aenea) (over 53 mm (Porter,
1982a; Habgood, 2003), and 50 rainbow skinks (over 35 mm (Clarke, 1965; Joss &
Minard, 1985)), were captured from three sites (F, K and L, see Section 2.7, Figure 2.2
& 2.3 for brief site descriptions and locations). Weight, SVL, tail and toe condition
were recorded for all animals (see Section 2.2.2), and skinks were individually marked
using xylene free silver ink prior to placement in an enclosure. Behavioural
34
observations and weight measurements were conducted between September and
November 2003.
2.6.1 Enclosure set up
The animals were housed in three custom-built reptile enclosures (Plate 2.5), 1 m x 2.4
m x 1 m in size (height x length x width), and placed indoors at The University of
Auckland. The enclosure room was lit by four ceiling mounted 900 mm fluorescent
tubes, and under a 14 hr 25 min:9 hr 35 min (Light:Dark) regime to mimic the mean day
length calculated for Auckland from December 2003 to February 2004 using
information supplied by Land Information New Zealand (LINZ, 2002). Temperature
was controlled by a DeLonghi electric radiator (Model ECC2400T) with the minimum
set at 23°C during the light period, and 15°C during the dark period to mimic the mean
maximum and minimum temperatures calculated for Auckland from December to
February (information from National Institute of Water & Atmospheric Research
(NIWA, 2004)). To monitor conditions and ensure animals did not overheat, and that
the environmental conditions of each enclosure were comparable, maximum and
minimum temperature and relative humidity was recorded manually at least once every
24 hours throughout the course of the experiment (Appendix III). In addition
dataloggers, recording temperature, relative humidity and light intensity every 15
minutes were installed in each enclosure for 23 days (Appendix III).
All enclosures contained the same amount of soil, leaf litter, plants and refuges (with
more refuges than skinks present in each enclosure). All enclosures had an Arcadia D3
reptile lamp (900 mm), fitted with an Arcadia 900 mm reflector installed centrally on
the roof to provide the necessary ultraviolet light conditions. The reptile lamps were
operated during the light period of each day, and controlled by an Arcadia fluorescent
lighting controller (C4 standard 25-30W). Throughout the course of the experiment the
lizards were supplied with a variety of wild caught live invertebrates as a food source,
and provided with drinking water. Upon completion of the experiment all animals were
released at their point of capture.
35
Plate 2.5 Interior view of one enclosure used for housing skinks during the behavioural experiment.
Photograph courtesy of J. Guilbert.
One enclosure housed six copper skinks (copper skink control), a second contained 30
rainbow skinks (rainbow skink control), and a third enclosure contained both species,
seven copper and 20 rainbow skinks (experimental enclosure). It was intended that 30
copper skinks would be housed in the copper skink control, and 10 copper skinks would
be housed in the experimental enclosure. These numbers were chosen upon
consideration of enclosure size and relative numbers of both species observed in
sympatric populations. However, the start of the experiment was delayed, and it was not
possible to collect the total number of animals desired.
36
2.6.2 Behavioural observation methods
2.6.2.1 Pilot study
A pilot study took place during August and September 2003, with all observations
conducted between 10:30 and 20:30 as informal observations had shown that the
animals were generally the most active during this time, and an indication of sampling
performance during times of peak activity was desired. During the pilot study
behaviours were categorised (Table 2.3) and a focal animal sampling regime of one
hour continuous observation was found to represent the behaviours of skinks best
(Appendix IV). A 10 minute waiting period at the beginning of each observational
session was chosen as skinks disrupted by the observer resumed their previous
behaviours in less than 10 minutes.
2.6.2.2 General observation methods
Behavioural observations were conducted by direct observation from a stationary
position outside the enclosures. Enclosures were systematically observed during the
light period from 08:40 to 22:40 with this time period broken up into seven two hour
sessions in which two focal animal observations and three scan observations, one hour
apart, were conducted (Table 2.4). During the experiment all enclosures were observed
twice at each session time. No observations were carried out until 24 hours had elapsed
after skinks’ weight measurements were taken, and this period of time has been
recorded as sufficient to allow lizard behaviour to acclimate to experimental conditions
(Downes & Hoefer, 2004), or seven days after major changes were implemented, e.g.
new animals added to enclosures. This was to avoid any short-term effects to the
animals’ behaviour caused by these disturbances affecting the results of the behavioural
observations. Observations were carried out using focal animal and scan observation
techniques, recommended by Martin & Bateson (1993) as suitable methods for studying
groups. At the start of an observation period the enclosure room was entered as quietly
as possible and the observer sat in position for 10 minutes prior to observations starting.
37
Movement and noise was kept to a minimum throughout the observations. To ensure
unbiased visual searches each enclosure was systematically searched from left to right
in three lengthwise strips. All focal animal and scan observations were carried out from
September to November 2003.
Table 2.3 Behaviour categories used for behavioural observations.
Behaviour Type Description
Aggressive contact State/Event Animal bit, or was bitten by, another skink
Basking State Animal was stationary, often with ventral
surface in contact with the substrate and legs
widely spread
Drinking State Animal ingested water
Foraging State Animal was searching through its surroundings,
i.e. looking around or under leaves or soil
Hidden State Animal was hidden from view either
completely or sufficiently to obscure other
behaviours
Mobile State Animal was walking, running or climbing
Non-aggressive contact State/Event Two or more animals touched but did not
exhibit signs of aggression
Scratching State Animal scratched itself
Stationary State Animal was stationary but ready to move, often
without ventral surface in contact with the
substratum to extent seen when basking
Predation Event Animal struck at an invertebrate prey item
Tail undulation Event Animal vibrated its tail
Tongue flick Event Animal rapidly protruded tongue from its
mouth
38
Table 2.4 Observation session times with an example of scan and focal animal observation organisation
given for the first session. Times in italics are approximate.
Session time Time Observation type
08:40 – 10:40 08:40 Scan 1
08:42 – 09:42 Focal animal observation 1
09:42 Scan 2
09:44 – 10:44 Focal animal observation 2
10:44 Scan 3
10:30 – 12:30
12:30 – 14:30
14:30 – 16:30
16:30 – 18:30
18:30 – 20:30
20:30 – 22:30
2.6.2.3 Focal animal observation methods
The first skink seen, that had not previously been a focal animal, was chosen; if all
emerged skinks had previously been observed, the first individual found was chosen.
The focal animal was observed continuously for one hour with all behaviours and
duration of behavioural states recorded. Due to low levels of observable activity by
copper skinks, observations of this species were taken opportunistically during the
second round of focal animal observations for the experimental enclosure, and
throughout observations for the copper control enclosure.
2.6.2.4 Scan observation methods
Behaviours of all emerged skinks were recorded; skinks not observed during scans were
recorded as hidden.
39
2.6.2.5 Data Analysis
Multiple focal animal observations of the same animal were averaged to give one value
per individual for each variable assessed (Martin & Bateson, 1993). As copper skinks
frequently lost their identification marks they could not be reliably identified
individually, and so copper skink focal animal observations were also averaged to
prevent pseudoreplication. Opportunistic observations of copper skinks were only
included in the analyses if individuals were observed from their emergence until their
retreat. Mean percentage of time spent in each behavioural state (Table 2.3) during the
focal animal observation period was calculated and graphed for each treatment to
identify predominant behaviours.
The total number of minutes each focal rainbow skink was observed basking, foraging
or hidden during the observation period was compared between control and
experimental enclosures using a Mann-Whitney U-test. The frequency of rainbow skink
aggressive contact, non-aggressive contact, predation, tail undulation and tongue flick
events observed during the focal animal observations were compared between rainbow
skink control and experimental enclosures using categorical data analysis (maximum
likelihood ANOVA) (SAS Institute, 1989-1996). In both instances the lack of reliably
independent observations of copper skinks and low amounts of observed behaviour for
that species prevented statistical tests being performed between copper skink control
and experimental enclosures; instead, measures were graphed to allow comparison
between all treatments.
The frequency of basking, foraging and hidden behavioural states observed during focal
animal and scan observations were compared between rainbow skink control and
experimental enclosures, and copper skink control and experimental enclosures using
categorical data analysis (maximum likelihood ANOVA) (SAS Institute, 1989-1996).
Percentage of animals in each treatment that were observed basking, foraging or hidden
during scans were plotted against hours of light duration. Mean durations of basking,
foraging and hidden behavioural states observed for each individual during focal animal
observations were calculated, with behaviours observed incompletely due to the start
40
and finish of the observation period excluded. As observation periods where only one
hour long the maximum duration of behaviour was one hour. Comparison of the mean
duration of basking and hidden behaviours of rainbow skink control and experimental
enclosures were performed using a Mann Whitney U test, and comparison of mean
duration of foraging was made using a t-test for unequal sample sizes. The lack of
observations that could be confirmed as independent for copper skinks and low amounts
of observed behaviour prevented statistical tests being performed between copper skink
control and experimental enclosures; instead these measures were graphed to allow
comparisons between all treatments.
2.6.3 Body condition measurement methods
Individual weight was tracked by capturing the skinks and taking SVL and weight
measurements (see Section 2.2.2) (Appendix V), to minimise handling stress a
maximum of ten measurements were taken throughout the experiment.
2.6.3.1 Data analysis
For individuals having over 50% of their tail (Petren & Case, 1996) individual body
condition was calculated as log weight and log SVL for each measurement taken during
the experiment, a mean value was then calculated for each measurement per treatment,
and a multiple linear regression was performed. The mean body condition from all
treatments, expressed as the residuals from each regression, were then plotted for each
measurement. The difference between the correlation coefficients gained for copper
skink control and experimental and rainbow skink control and experimental were
compared using the difference between two correlation coefficients test STATISTICA
version 6 (StatSoft, 2001).
41
2.7 Study sites
Short descriptions of study sites follow with capital letters in parentheses referring to
map positions on Figure 2.2 or 2.3 (see Appendix VI for latitude, longitude and altitude
data). Habitats investigated at each site are noted at the end of each description (see
Table 2.1 for abbreviations and habitat descriptions).
(A) Whangarei (Figure 2.2)
Northcroft Drive, Kamo
A mostly pastoral site divided by tree windbreaks and lined by mature native and exotic
trees with areas of rank vegetation underneath. RV
(B) Wenderholm Regional Park, Wenderholm; (C) Long Bay Regional Park, Long Bay
(Figure 2.3)
Parks with onsite nurseries, a variety of service buildings and uncovered dry storage
areas. HM
(D) Albany Heights Road, Albany (Figure 2.3)
A residential property with extensive gardens (many covered with weed mat) and a
variety of surrounding buildings. HM
(E) Muriwai Regional Park, Muriwai (Figure 2.3)
A park with an onsite nursery, wood storage area, a variety of service buildings and a
ranger station. HM
(F) Don Bucks Road, Massey (Figure 2.3)
An operating nursery with disused and utilised glasshouses, uncovered storage areas
and plant storage areas covered with weed mat. Seven Black Trakka tunnels were
42
installed as skink refuges from March to November 2003; five of these in a plastic-
house and two in an adjacent shade-house where rainbow skinks had been observed.
HM, RV
(G) Awhiorangi Promenade, Swanson (Figure 2.3)
A residential property with extensive gardens, a variety of nearby buildings and storage
areas surrounded by rank vegetation. HM, RV
(H) Rosebank Road, Avondale (Figure 2.3)
An industrial site with a variety of uncovered storage areas surrounded by rank
vegetation. Fifteen Black Trakka tunnels were installed as skink refuges from March to
April 2003; twelve skink refuges were installed along the site perimeter, and three
around a container utilised for storage where rainbow skinks had been observed. HM,
RV
(I) Arataki Nursery, Waitakere (Figure 2.3)
A nursery surrounded by native bush with a variety of service buildings, uncovered
storage areas and plant storage areas covered with weed mat. HM
(J) Omana Regional Park (Figure 2.3)
A park with assorted buildings, storage areas and a revegetated section of trees planted
in approximately 1993 (G. Ussher pers. comm.). HM, S
(K) Price Crescent, Mount Wellington (Figure 2.3)
A residential property with substantial gardens and a woodshed; five Black Trakka
tunnels were installed as skink refuges from July to November 2003 along the back
perimeter fence under native trees where copper skinks had been observed. HM
43
(L) Bleakhouse Road, Howick (Figure 2.3)
A residential property in a highly urban area with a small garden. HM
(M) Corner of Ormiston Road and Te Irirangi Drive, Otara (Figure 2.3)
A revegetated site that was replanted in approximately 1999 (A. Jenks pers. comm.)
with a variety of native trees, which have grown well but are overgrown by weeds in
places despite the initial use of mulch and weed mat. Fifteen Black Trakka tunnels were
installed as skink refuges from February to November 2003 amongst the plantings
where rainbow skinks had been observed. S
(N) Tapapakanga Regional Park, Tapapakanga (Figure 2.3)
A park with a variety of buildings and hard storage areas, in addition to areas of
grassland and scrublands (replanted in approximately 1998 (G. Ussher pers. comm.)).
HM, RV, S
(O) Regional Botanic Gardens, Manurewa (Figure 2.3)
Park with an onsite nursery, a variety of service buildings and uncovered dry storage
areas. HM
(P) Whatipu, Waitakere Ranges (Figure 2.3)
A park with substantial gardens, various buildings and storage sheds. HM
(Q) Awhitu Regional Park (Figure 2.3)
A park with a variety of buildings, storage sites, rank vegetation and revegetated areas
planted in approximately 2002 (G. Ussher pers. comm.). HM, RV, S
44
(R) Tauranga (Figure 2.2)
Robbins Park: an inner city park with assorted gardens, a hothouse, storage buildings
and areas of mature trees with lawn beneath. HM
Tauranga railway: a stretch of inner city railway line surrounded by rank vegetation and
industrial sites. HM, RV
Waikareao Walkway: a walkway through an area revegetated with assorted native trees
that back onto a rank vegetation covered bank with residential properties at the top.
HM, RV
(S) Gisborne (Figure 2.2)
Kaiti Beach Road: a road bordered by residential properties, rank vegetation and
Titirangi Recreational Reserve. Mature trees, with leaf litter and refuse beneath, them
are found at several points along the roadside. RV
Cook Landing: revegetated and lawn areas next to Eastland Port Ltd buildings.
Regeneration is occurring under the plantings, there are also logs and litter (bark and
leaves) on the ground. S
Titirangi Recreational Reserve: an abandoned driveway bordered by rank vegetation.
RV
Gisborne railway station: an area of rank vegetation between railway lines and
Waikanae Creek, with rank vegetation and overgrown gardens surrounding the railway
buildings. RV
Plant nursery: an operating nursery and garden centre surrounded by native plantings
with uncovered storage areas and plants stored on weed mat covered areas. HM
(T) Napier (Figure 2.2)
Napier Travel Centre: an area of rank vegetation with several mature trees, and places
where refuse had been dumped. RV
Portside car park: a gravel car park at the base of cliffs with rank vegetation between the
parking area and the cliff base where garden refuse had been dumped and fallen stones
had accumulated. RV
45
Native plant nursery: an operating nursery with glasshouses, extensive gardens (often
with weed mat covering bare ground), residential buildings, covered and uncovered
storage areas. HM
(U) Wanganui (Figure 2.2)
Heads Road railway: an unused railway line, with a lot of refuse built up against the
railway siding, running between a road and residential and industrial buildings. HM
Balgownie Wetlands: a walkway area revegetated with various native species under
which leaf litter, fallen and cut branches and refuse had collected. S
Brunswick Road railway: a railway running between paddocks and industrial sites with
a considerable amount of partially overgrown refuse dumped beside the railway siding
at one point. RV
(V) Wellington (Figure 2.2)
Garden centre: an operating garden centre backing onto native bush. HM
Karori wasteland: an area of rank vegetation with substantial amounts of refuse dumped
in parts. RV
Reclaimed land: an area of rank vegetation surrounding the Wellington airport and
industrial sites with refuse dumped at several points. RV
Houghton Bay Road: an area revegetated with a variety of native species, shredded bark
had been utilised as mulch. S
(W) Nelson (Figure 2.2)
Basin Reserve: car park and picnic area next to a cliff replanted with native and exotic
species; fallen rocks had accumulated at the cliff base. S
Centre of NZ Lookout: hilltop replanted with native species, infrequently mown grass
and log piles are found between plantings. S
Nursery: an operating garden centre and nursery with glasshouses, uncovered storage
areas and plants stored on areas covered with weed mat. HM
46
(X) Blenheim (Figure 2.2)
McArtney Road railway: a stretch of railway running between industrial sites and
bordered by rank vegetation with small amounts of accumulated refuse. RV
Taylor River Reserve: a park surrounded by residential properties with replanted areas,
extensive lawn with occasional potential refuges. HM
Nursery: an operating garden centre and nursery with glasshouses, uncovered storage
areas, and plants stored on weed mat. (HM)
47
Figure 2.2 Location of study sites outside of the Auckland region (A and R to X) (Eagle Technology
Group, 2000). Refer to Figure 2.3 for an enlargement of the framed region and Auckland study sites.
Letters in parentheses refer to study site descriptions. Map prepared with assistance from P. Barnett.
50 km
N
�
Whangarei (A)
Tauranga (R)
Gisborne (S)
Napier (T)
Wanganui (U)
Wellington (V) Nelson (W)
Blenheim (X)
37°S
175°E
40°S
48
Figure 2.3 Location of Auckland region study sites (B to Q) (Auckland Regional Council (2003)). Letters
in parentheses refer to study site descriptions. Map prepared with assistance from P Barnett.
Wenderholm (B)
Long Bay (C)
Muriwai (E)
Albany (D)
Massey (F)
Swanson (G)
Avondale (H)
Arataki (I)
Whatipu (P)
Waitakere Ranges
Manukau Harbour
Mt Wellington (K)
Howick (L)
Otara (M)
Botanic Gardens (O)
Tapapakanga (N)
Awhitu (Q)
Omana (J)
Hauraki Gulf
N
�
10 km
Waitemata Harbour
49
3 Current and predicted distribution
3.1 Introduction
Geographic distribution is a fundamental aspect of species ecology, and the predicted
distribution of potentially invasive species plays a major role in management actions
ranging from quarantine and border security to monitoring and control. Overall species
distribution is controlled by myriad interactions between the species and its biotic and
abiotic environment (Nix, 1986; Mitchell, 1991). Within the set of abiotic conditions
climate may delimit the geographic distribution of a species (Carter & Prince, 1988;
Panetta & Mitchell, 1991b). However, these climatic conditions also act in concert with
an individual’s physiology (Salinger et al., 1989), and requirements such as site
availability, in a dynamic and intricate way (Carter & Prince, 1988). The picture is more
convoluted when dealing with animal species, as the flexibility of many behaviours may
allow persistence under marginal conditions, for example oviposition site may vary in
depth to avoid lethal temperatures and permit successful reproduction.
Climate ultimately plays a large part in species distribution (Mitchell, 1991) due to the
wide range of climates available globally and the relatively narrow species tolerances
(Mitchell & Williams, 1996). Given otherwise ideal conditions and adequate dispersal
to a location, if it is outside the climatic tolerance of a species then the species will not
be able to persist there (Mitchell & Williams, 1996). However, individuals may be able
to survive due to the presence of microhabitats, where a population would be unable to
develop (Carter & Prince, 1988). Species distribution constraints may be viewed in
terms of a hierarchy of effects (Mitchell et al., 2004); if climate requirements are met,
then establishment of a species relies on a number of other conditions also being met,
such as circumstances necessary for successful reproduction (Carter & Prince, 1988;
Mitchell, 1991). In the case of rainbow skinks (Lampropholis delicata) correct
conditions for both adult and egg stages must be fulfilled for a breeding population to
establish. The likelihood of intentionally introduced species establishing in a new
50
environment is negatively correlated with increasing bioclimatic dissimilarity between
source and new locations (Nix & Wapshere, 1986).
Homocline analysis seeks to describe physical limits to species distribution and match
these to wider geographic areas (Nix & Wapshere, 1986). Climate models are an elegant
way of performing such analyses, and have been used to investigate potential
distributions of weed species (see Howden, 1985; Panetta & Mitchell, 1991a, b), and
assess native plant and animal distributions (see Busby, 1986; Nix, 1986; Hill et al.,
1988; Booth, 1990; Mitchell, 1991; Brereton et al., 1995; Mitchell & Williams, 1996).
The Bioclimatic Prediction System computer programme (BIOCLIM) (Nix, 1986;
Busby, 1991) has been used to investigate the distribution of many different species (see
Prendergast & Hattersley, 1985; Busby, 1986; Longmore, 1986; Hill et al., 1988), and
has been helpful in elucidating climatic factors limiting distribution of focal species
(Busby, 1991).
Climate modelling allows species distribution based on climatic conditions to be
mapped; using climate surface techniques such as those developed by Hutchinson &
Bischof (1983) and Nix (1986) to gain site specific climate estimates. Therefore the
presence or absence of a species for which a climate profile is known can be predicted
on a site-by-site basis. Nix (1986) investigated the distribution of Australian elapid
snakes using a resolution of 0.5º for continent wide considerations of species, and
suggests that a resolution of 0.02º may be developed using the BIOCLIM programme.
The climate profile for rainbow skinks was developed by considering parameters at
record sites from Australia and New Zealand; from these predicted New Zealand
distributions (based on a 500 x 500m grid) were mapped by considering each location
against the climatic profile.
51
3.1.1 Objectives
This chapter examines the current and predicted distribution of rainbow skinks in New
Zealand. Records of rainbow skink occurrence throughout New Zealand were compiled,
in addition climate modelling techniques were used to map their potential distribution.
3.2 Results
Three hundred and thirteen Australian distribution records for rainbow skinks were
compiled and mapped (Figure 3.1) (Appendix I). Figure 3.1 depicts the mainly
southeastern distribution of rainbow skinks in Australia, and their range from Cairns to
Tasmania. One hundred and forty five of these records were used to create a climate
profile (Table 3.1), and from this a predicted New Zealand distribution was mapped
(Figure 3.2) (Appendix I). Records were not used if they did not have appropriate
climate data or were duplicates. The predicted distribution of rainbow skinks in New
Zealand based on this climate profile was largely coastal and includes some
northeastern offshore islands and a small number of restricted South Island locations
(Figure 3.2).
Sixty-three New Zealand distribution records for rainbow skinks were compiled and
mapped (Figure 3.1, 3.2 & 3.3) (Appendix I). These records are mainly from disjunct
locations in the North Island (ranging from Whangarei to Wanganui). Using the climate
profile generated from 61 records (Table 3.2) a predicted distribution of rainbow skinks
was derived (Figure 3.3) (Appendix I). Figure 3.3 shows a much larger proportion of
New Zealand as suitable for rainbow skink survival than Figure 3.2, and includes inland
areas in addition to coastal locations. Although the range does not extended in latitude,
habitable areas in the South Island are less constrained.
52
Figure 3.1 Map showing Australian rainbow skink distribution records compiled. Black squares denote
records used in BIOCLIM analysis; red squares denote records not used in BIOCLIM analysis.
Australian and New Zealand data sets were combined to produce a climate profile
(Table 3.3), which was used to map predicted rainbow skink distribution considering
the widest climatic envelope (Figure 3.4) (Appendix I). The range extends slightly to
the north, and more inland and South Island locations appear suitable. Comparison of
recorded populations and widest predicted distribution indicate that rainbow skinks
have yet to be range limited by temperature and rainfall in New Zealand.
Rainbow skink surveys were conducted at 34 sites (Table 3.4), where they were
predicted to occur given the following results (Figure 3.3 & 3.4). Rainbow skinks were
found at four sites in the North Island (Table 3.4); 12% of the total surveyed.
Temperature, relative humidity and general weather conditions experienced during
surveys were recorded and are detailed in Appendix VII.
40°S
25°S
10°S
140°E
500 km
53
Figure 3.2 Predicted rainbow skink distribution (depicted by red shaded area) based on Australian
records; blue stars indicate sites of known occurrence.
100 km
N
�
54
Figure 3.3 Predicted rainbow skink distribution based on New Zealand records. Conventions as Figure
3.2.
100 km
N
�
55
Figure 3.4 Predicted rainbow skink distribution based on Australian and New Zealand records.
Conventions as Figure 3.2.
100 km
N
�
Table 3.1 Climate profile of rainbow skinks based on Australian records. Temperature measurements are mean amounts in °C; rainfall measurements are total amounts in mm
(see Mitchell, 1991).
Annual
mean
Highest mean
monthly
Lowest mean
monthly
Range Seasonality Wettest
quarter
Driest
quarter
Coldest
quarter
Warmest
quarter
Min temp 12.39 20.10 4.07 12.55 0.98 9.60 9.18 8.69 15.26
Max temp 22.32 35.70 7.88 28.94 1.39 27.81 20.81 15.69 28.39
Min rainfall 9.87 9.87 0.00 9.87 0.28 9.87 0.00 0.00 0.00
Max rainfall 2270.89 322.74 69.93 255.83 12.00 877.42 251.03 868.92 490.23
Table 3.2 Climate profile of rainbow skinks based on New Zealand records. Measurements as Table 3.1.
Annual
mean
Highest mean
monthly
Lowest mean
monthly
Range Seasonality Wettest
quarter
Driest
quarter
Coldest
quarter
Warmest
quarter
Min temp 10.89 19.10 2.46 15.58 1.04 7.32 9.10 6.80 14.56
Max temp 15.60 25.13 7.77 21.94 1.67 11.61 19.66 11.61 19.42
Min rainfall 852.81 79.74 52.36 23.61 0.32 226.89 172.62 215.58 172.62
Max rainfall 1799.15 215.86 103.41 114.01 0.83 592.94 331.02 592.94 331.02
Table 3.3 Climate profile of rainbow skinks based on New Zealand and Australian records. Measurements as Table 3.1.
Annual
mean
Highest mean
monthly
Lowest mean
monthly
Range Seasonality Wettest
quarter
Driest
quarter
Coldest
quarter
Warmest
quarter
Min temp 10.89 19.10 2.46 12.55 0.98 7.32 9.10 6.80 14.56
Max temp 22.32 35.70 7.88 28.94 1.67 27.81 20.81 15.69 28.39
Min rainfall 9.87 9.87 0.00 9.87 0.28 9.87 0.00 0.00 0.00
Max rainfall 2270.89 322.74 103.41 255.83 12.00 877.42 331.02 868.92 490.23
57
Table 3.4 Presence/absence of rainbow skinks at sites surveyed. Letters in parantheses denote study site
(Figure 2.2 &2.3).
City Site (Notation) Area searched
(m2)
Person
hours
Presence/
absence
Whangarei Kamo (A) 1000 2:10 Absent
Auckland Wenderholm Regional
Park (B)
770 2:34 Absent
Auckland Long Bay Regional Park
(C)
1370 4:14 Absent
Auckland Muriwai Regional Park (E) 1151 1:34 Absent
Auckland Arataki Nursery (I) 1680 2:16 Absent
Auckland Omana Regional Park (J) 3900 1:10 Absent
Auckland Tapapakanga Regional
Park (N)
4500 0:25 Absent
Auckland Regional Botanic Gardens
(O)
3500 1:00 Absent
Auckland Whatipu (P) 20000 0:58 Absent
Auckland Awhitu Regional Park (Q) 2400 1:15 Absent
Tauranga Robbins Park (R) 6700 0:38 Present
Tauranga Tauranga railway (R) 8800 0:40 Present
Tauranga Waikareao Walkway (R) 6000 2:12 Present
Gisborne Kaiti Beach Road (S) 10000 1:20 Absent
Gisborne Cook Landing (S) 2000 1:57 Absent
Gisborne Titirangi Recreational
Reserve (S)
1000 0:27 Absent
Gisborne Gisborne railway station
(S)
1000 0:31 Absent
Gisborne Plant nursery (S) 585 1:06 Absent
Napier Napier Travel Centre (T) 27500 0:48 Absent
Napier Portside car park (T) 3000 2:09 Absent
Napier Native plant nursery (T) 205 0:41 Absent
Wanganui Heads Road railway (U) 2700 0:45 Absent
Wanganui Balgownie Wetlands (U) 2542 1:29 Absent
Wanganui Brunswick Road railway
(U)
15400 3:40 Present
Wellington Garden Centre (V) 500 0:58 Absent
Wellington Karori wasteland (V) 1175 0:35 Absent
Wellington Reclaimed land (V) 900 0:29 Absent
Wellington Houghton Bay Road (V) 30000 0:51 Absent
Nelson Basin Reserve (W) 600 0:30 Absent
Nelson Centre of NZ Lookout (W) 1050 0:39 Absent
Nelson Nursery (W) 3900 1:09 Absent
Blenheim McArtney Road railway
(W)
2600 1:41 Absent
Blenheim Taylor River Reserve (W) 654 0:26 Absent
Blenheim Nursery (W) 25 0:29 Absent
58
3.3 Discussion
The results of compiling records and surveying new areas provide a basis for predicting
general distribution of rainbow skinks in New Zealand. Temperature and rainfall
regimes of areas currently occupied by rainbow skinks; may be viewed as important
determinants of their fundamental niche (Brereton et al., 1995; Mitchell & Williams,
1996). If the additional effects of biota, dispersal limitations, habitat and reproductive
requirements were considered the suitable area for rainbow skinks would be expected to
reduce to a realised niche (Brereton et al., 1995; Mitchell & Williams, 1996). Rainbow
skinks occupy a large native range (Forsman & Shine, 1995a), including south eastern
coastal areas of Queensland, New South Wales, and Victoria in addition to South
Australia and Tasmania (Figure 1.1 & 3.1). This resulted in a climate profile (Table 3.1)
with high rainfall tolerances, similar to the profile found for one-leaf Cape tulip
(Homeria flaccida) by Panetta & Mitchell (1991b). Species with large native ranges
often exhibit wide climate tolerance, and show broad predicted distributions
(Prendergast & Hattersley, 1985; Hill et al., 1988). This is certainly the case with
rainbow skinks, which show broad climate profiles (Tables 3.1, 3.2 & 3.3) and an
extensive predicted distribution in New Zealand when the full climate profile is
considered (Figure 3.4).
Assessing the potential distribution of an introduced species in a new environment is
more complex than for a native species as dispersal since introduction must be
considered. Rainbow skinks require access to an area before they can establish there,
and sites accessed must possess sufficient conspecifics to allow successful breeding
(Carter & Prince, 1988). Other biotic factors that might limit species establishment at a
site include the presence of competitors, predators, pathogens, (Nix, 1986; Mitchell,
1991), parasites and absence of prey species (Nix, 1986). In the case of an exotic animal
the potential of novel biotic factors to prevent establishment may be lessened as the
species has not evolved in that ecosystem, and therefore may not be recognised as prey
or a suitable host. Conversely greater overlap may occur with competitors as the
59
evolution of niche separation would not have occurred, and an introduced species might
be more susceptible to pathogens and parasites it has not evolved resistance to.
In climatically suitable areas rainbow skinks might be limited by habitat. Rainbow
skinks occupy a vast range of habitats (see Section 1.2.2 & 4.2.1); however, it has not
regularly been recorded in New Zealand native bush. It is possible that native forest
would be too cold or wet for an Australian reptile, although rainbow skinks do naturally
occur in Tasmania, and Tasmanian plant species have been found to persist in areas of
higher precipitation than northern Australian species (Hill et al., 1988). Additionally,
two records from the DoC (New Zealand Department of Conservation) Amphibian and
Reptile Database list broadleaf forest a habitat occupied by rainbow skinks (Table 1.2),
and they have been recorded in human inhabited areas of the Waitakere Ranges (S.
Chapman pers. comm.). Rainbow skinks have been present in New Zealand since the
1960s (Gill & Whitaker, 2001), so it is possible they have adapted to the novel
conditions. As previously noted for brushtailed possum (Trichosurus vulpecula), it is
not unusual for animals to show marked change in the face of a new environment
(Section 1.1). Anthropogenic factors may also play a role in extending the distribution
of a species by creating colonisable sites beyond the current range (Carter & Prince,
1988). Hence the future distribution of rainbow skink may rely upon human
manipulation of climate, e.g. glasshouses, allowing the species to colonise and possibly
invade surrounding areas.
The importance of biotic and abiotic factors in limiting species occurrence will depend
on the location considered. A species is less likely to be limited by stochastic or biotic
processes in the centre of its range than at the edge, where marginal climate can also
come into play (Mitchell, 1991). As species distribution limits are reached site specific
factors become more critical in determining survival and establishment of individuals,
and so abundance declines (Mitchell, 1991) and populations may become less common
(Carter & Prince, 1988). Unrelated factors may together impose limits at the range edge,
e.g. availability of suitable habitat and successful reproduction (Carter & Prince, 1988).
If the native distribution of rainbow skinks alone is considered then New Zealand
populations are far from the centre of the range. However, given their successful
60
establishment and dispersal in New Zealand we might consider the Auckland region the
core, and areas of potential occurrence such as Marlborough and Christchurch the
margin (Figure 3.4). In these edge areas predation pressure and possible competition
from native lizards might limit establishment of rainbow skinks. Additionally if rainbow
skinks exert competitive pressure on native reptiles, the strength of this interaction
would not necessarily be constant throughout their distribution and impacts might only
be observed where native species are already compromised in some way (Towns et al.,
2001). Unfortunately this situation applies to most areas of mainland New Zealand,
especially in highly fragmented landscapes such as the North Island (Towns et al.,
2001), mainly due to habitat destruction and predation from introduced species (Dick,
1980a; Freeman, 1997; Towns et al., 2001).
When both Australian and New Zealand records were used to predict rainbow skink
distribution (Figure 3.4) the suitable area increased extensively from those derived
using only one set of records (Figures 3.2 & 3.3). This is similar to the results of Panetta
& Mitchell (1991a) for Johnson grass (Sorghum halepense); when only Australian
records were used to generate a map of New Zealand distribution the actual distribution
found was not reflected. Panetta & Mitchell (1991a) concluded that the climate profile
based on Australian data alone did not encompass the full range of climates habitable by
this species, i.e. New Zealand has habitats that are not present in Australia, but which
Johnson grass can occupy. Another facet of this is escape from competitors, predators,
pathogens, and parasites by movement to a new environment and hence the ability to
occupy a wider range of areas relative to the native range (Mitchell, 2004 in prep.). This
is a frequent observation of species released into environments outside their native
range, and indicates tolerance not apparent under natural situations (Mitchell &
Williams, 1996). Such plasticity is possibly exacerbated in rainbow skinks as they are
extremely variable; there have been four types, that potentially qualify as separate
species, found within the species complex (Mather, 1986; Mather, 1990). The types and
frequencies of each L. delicata type present in New Zealand, may affect the potential of
this species to expand even further than the predicted distributions.
61
Predicted distributions (Figures 3.2, 3.3 & 3.4) show potential for rainbow skinks to
colonise Nelson, Marlborough and Christchurch regions. Based on natural dispersal this
seems unlikely as the nearest recorded population is Wanganui (Figure 3.3 & 3.4) and
they are small animals with limited powers of natural dispersion (Anderson & Burgin,
2002). However, due to human aided dispersal animals from Australian and New
Zealand populations are reaching Christchurch (Whitaker, 1998, 2002b, c, 2003g) and
Nelson (Whitaker, 2003h). Through anthropogenic dispersal rainbow skinks may cross
areas not suitable for colonisation to be deposited in favourable locations. This appears
similar to the situation in the Hawaiian Islands where rainbow skinks were accidentally
introduced to O’ahu in approximately 1917 ( Oliver & Shaw, 1953 recorded as
Lygosoma metallicum), and spread to all major human inhabited islands largely by
inadvertent human transportation (Baker, 1979). Although no records of rainbow skink
populations were found for Napier, conversations with garden centre staff and residents
indicated lizard eggs and live rainbow skink adults had been transported to the city with
plants from Auckland. This highlights a great risk of invasion into areas that are
revegetated, and is a concern given the number of offshore islands replanted utilising
plants in potting mix brought from the mainland. To combat this risk onsite nurseries
using sterile growing media would be required, such measures would also assist in
attempts to keep islands free of confirmed invasive species such as Argentine ant
(Linepithema humile).
Possible climate change presents another consideration (Panetta & Mitchell, 1991b),
with increases of mean annual temperature likely to occur in New Zealand (Mitchell &
Williams, 1996). Scenarios of 0.5-5°C temperature increase, and seasonal rainfall
reduction for some districts are possible over time (Whetton et al., 1996). Due to this it
has been suggested that pest, parasite and disease species may extend southwards in
New Zealand (Salinger et al., 1989; Prestidge & Pottinger, 1990), and due to warming
expected in Australia, Australian species may increase in altitudinal range (Brereton et
al., 1995). The same trend of southward and altitudinal range extension might be seen
for rainbow skink in New Zealand if temperature limits populations. It is interesting to
note that in the Hawaiian Islands rainbow skinks have been recorded at the highest
elevation for a reptile (Baker, 1979), possibly due to mild temperatures experienced in
this state. Rainbow skinks have a potentially wide genetic makeup, which may allow
62
them to adapt to climate change (Brereton et al., 1995). However, the climate changes
suggested are expected to occur too swiftly for natural adaptation or dispersal to
favourable environments to accommodate (Mitchell & Williams, 1996).
As rainbow skinks are native to Australia they would be expected to withstand warmer
climates than native New Zealand lizards. Especially since the last major climatic era
was colder than present, and therefore species naturally occupying New Zealand might
show adaptations to colder climates (Mitchell & Williams, 1996). A possible cold
adaptation that has received much attention are viviparous reptiles (e.g. Robb, 1974;
Spellerberg, 1976; McGregor, 1977; Tinkle & Gibbons, 1977; Shine, 1983; Shine,
1985a, b; Qualls & Shine, 1998a), this trait is highly correlated with cold climates in
Australia (Spellerberg, 1976; Shine, 1985b), and observed in all but one native New
Zealand species (Robb, 1974; Bell et al., 1983; Robb, 1986; Cree, 1994; Higham, 1995;
Gill & Whitaker, 2001). Should native species be lost from locations due to climate
change this might enhance survival and persistence of non-indigenous species (Mitchell
& Williams, 1996). However, should a range extension become possible for rainbow
skinks it would hinge on the magnitude and speed of climate change, and occur in
concert with a multitude of other responses which could enhance or restrain extensions.
3.3.1 Considerations
Predicted distributions were formed with the requirement that “suitable” locations lie
within each parameter of the known climate profile of rainbow skinks. This follows
assumptions of the technique used by Mitchell (1991) where each parameter is
considered of equal weight. Analysis of the climate profile using the methods of Yee &
Mitchell (1991) may elucidate which variables are most important to rainbow skink
distribution. The methods they utilised analyse the climate profile calculated for a
species using generalised additive models and allow the variables considered, e.g. mean
monthly rainfall, to be weighted (Yee & Mitchell, 1991). Examination of environmental
variable effects on adult and egg stages would also be valuable in ascertaining whether
all parameters used should have the same weight, even though overall distribution
63
cannot be predicted by physiological tolerance alone (Carter & Prince, 1988). The
climate profiles considered 18 temperature and rainfall variables, which are likely to be
key variables in determining rainbow skink distribution. The model would benefit from
consideration of further climatic variables such as solar radiation and relative humidity,
which are also likely to be important to a reptile species, and additional Australian
rainbow skink records and weather data. The possibility of rainbow skink adaptation,
and the discovery of four types of rainbow skink within the species complex (Mather,
1986; Mather, 1990), makes it pertinent to reassess the physiological tolerances and
optimums of adults and eggs previously gained from Australian animals (see
Spellerberg, 1976; Shine, 1983; Graham, 1987) using New Zealand populations.
Physiological experiments may also be used to determine climatic tolerance not yet
visible under natural conditions. Together these results could be used to hone future
predicted distribution models.
3.3.1.1 Scales of measurement
A constraint of climate surfaces is the treatment of landscape as though it was level
when features may create differences between certain locations and the surrounding
area, in terms of temperature and rainfall (Mitchell, 1991). Although information for the
climate surfaces was realistic (Nix, 1986; Mitchell, 1991), and was gathered from the
environment, the surfaces may not reflect actual conditions, especially for sites with a
relatively short climate record (Mitchell, 1991). Problems due to this would be expected
at species distribution borders, or where severe but sporadic frosts may limit occurrence
(Mitchell, 1991). It is easily possible for localised climates to err from regional trends
(Howden, 1985), and therefore not be recorded as suitable or adverse (Booth, 1990).
Although the maps were produced using a climatic grid of 500 x 500 m, areas of steep
terrain, and hence dramatic temperature and rainfall changes, may have larger
deviations from predicted values (Nix, 1986). As the BIOCLIM system develops to
encompass other environmental factors and the calculation of more subtle information
than presently available (Nix, 1986) the current analysis would benefit from re-
assessment using this system. It would also profit from refinement based on habitat,
64
particularly human modified habitats and urban areas, looking at what habitats are
available within the predicted distribution that rainbow skinks do and do not utilise.
A requirement for accurate species distribution maps based on climate is that the species
is limited by climate, and has spread to reach its climatic limits in the source region
(Howden, 1985; Panetta & Mitchell, 1991b; Mitchell & Williams, 1996). The species
must persist throughout its climatic niche to enable its description, and be limited by
non-climatic factors where it does not occur within the niche (Mitchell & Williams,
1996). When species distributions are limited by factors other than climate, e.g. habitat
availability, BIOCLIM will not prove as useful (Busby, 1991). As reptiles are
ectotherms, and therefore rely upon external heat sources, it seems reasonable to assume
temperature would have a large bearing on potential occurrence. The geographic
distribution and life characteristics of reptiles are principally dictated by temperature
(Spellerberg, 1976). Indeed the thermal niche of a reptile has been described as
“probably the single most important component of a reptile’s ecology” (Davies et al.,
1980). Since the final climate profile (Table 3.3) for rainbow skinks was derived from
New Zealand and Australian records it is possible for this species to survive at the limits
of the variables given. However, the ability of rainbow skinks to inhabit climates of
every temperature and rainfall combination from minimum to maximum has not been
investigated by this project. Although it seems likely rainbow skinks have reached their
distribution limits in Australia, it is obvious from comparison of maps based on
Australian records (Figure 3.2), versus New Zealand records (Figure 3.3) that the full
range of climates tolerated by rainbow skinks are not present in their native country.
Should only records from the native range have been considered the potential spread of
rainbow skinks in New Zealand would have been severely underestimated.
3.3.1.2 Genetic homogeneity
It has been stated that genetic homogeneity is a requirement for the valid use of
correlative models (Howden, 1985), e.g. BIOCLIM, and that there are not further
climates the species might adapt to (Mitchell & Williams, 1996). Vickery (1974)
65
demonstrated growth peaks in the genetically heterogeneous plant Mimulus guttatus that
occurred under significantly different thermal conditions from growth peaks observed
previously. This suggested individuals showed preadaptation to thermal environments
not normally experienced. The same may well be true for rainbow skinks, with some
individuals having the potential to survive and reproduce in climates they do not
presently utilise due to currently untapped genetic potential. The assumption of genetic
homogeneity was possibly not met by Johnson grass distribution research (Panetta &
Mitchell, 1991a), and given the genetic diversity recorded within rainbow skinks
(Mather, 1986; Mather, 1990) would not appear to be met by this research either. Due to
the hardiness and flexibility of rainbow skinks, and their potentially high level of
genetic diversity, the reliability of predicted distributions would be expected to be lower
than for a genetically homogenous species (Panetta & Mitchell, 1991b). Future research
to investigate which taxa of the L. delicata species complex are found in New Zealand,
and whether they may be considered equivalent in terms of potential distribution and
impact would be most valuable.
Surveys for rainbow skinks were necessarily brief and site specific due to financial and
time constraints. In addition the hand search survey technique used may be unreliable,
especially over a short term, as it is highly dependent on a number of factors including
weather, which affects reptile activity (Whitaker, 1968; Vogt & Hine, 1977; Karns,
1986; Hayes et al., 1989), and skinks being inaccessible or not apparent when in
refuges. However, these constraints were minimised as surveys were conducted during
early summer in periods of fine weather, when possible, which is when lizards are often
most active (Karns, 1986; Hayes et al., 1989). Rainbow skinks were detected during
these surveys, and this species tends to be more visible, especially at high densities, than
many native skinks (pers. obs.). Experienced herpetologists familiar with the species
conducted the surveys in an attempt to equalise search effort and minimise differences
in detection which may be experienced especially when the species is fast moving (Vogt
& Hine, 1977; Karns, 1986), as rainbow skinks are (Lark, 1984; pers. obs.).
66
3.3.1.3 Future surveys
It is certain that rainbow skinks have a more extensive range than discovered by the
limited investigation of this research. To extend the survey coverage temporally and
spatially would be pertinent, and researchers have recommended short survey periods
spread over a range of habitats and throughout times of anticipated activity at each
survey site (Vogt & Hine, 1977). Should long term monitoring be undertaken, a
standard technique including details such as area searched, search time, and protocol for
separating established populations from intercepted individuals should be formed.
Future surveys could be compared to current predicted distributions to update details of
spread and test model accuracy over time. In addition maintaining contact with regional
representatives of the New Zealand Herpetological Society and DoC, and a survey of
garden centres and nurseries, where rainbow skinks are often intercepted, would
undoubtedly prove of great benefit with site visits conducted as required. However,
species record quality and quantity will always be dependent on the attention of
observers (Williamson & Brown, 1986). If rainbow skinks are overlooked due to their
small size and plain colours then they may remain unreported in areas where they are
abundant unless specific enquiry is made.
Rainbow skinks reach very high densities (Baker, 1979; Forsman & Shine, 1995a;
Cogger, 2000; pers. obs.), but this may not be true for all areas they occupy. Research to
examine at what abundance levels they begin to exhibit a negative influence, should one
prove detectable, and correlations of this with climate, land use, and existing species
assemblages are required to fully realise potential risks. In highly impacted sites, e.g.
large subdivisions, rainbow skinks would be unlikely to persist, however, if accidentally
introduced to Tiritiri Matangi Island, a mammalian predator free offshore island, they
could potentially reach high numbers.
67
3.3.2 Conclusions
The results indicate rainbow skinks have not reached their potential distribution in New
Zealand and may spread inland and much further south of their current known range.
Given their propensity to disperse with human aid rainbow skinks may well invade new
offshore islands and suitable locations disjunct from areas with established populations.
Many of the northeastern offshore islands appear to have suitable climates for rainbow
skinks and are adjacent to mainland areas possessing or with potential populations.
Despite the caveats inherent to this research it is better to have an indication of potential
rainbow skink distribution that is under or over estimated, than no prediction at all. It is
obvious that rainbow skinks have great dispersal ability and are hardy enough to survive
human disturbance in transit and in their habitat. If there are areas where they are not
wanted, e.g. offshore island sanctuaries, it is imperative that steps are taken now to
prevent their invasion.
68
4 Habitat use and general morphological features of
different populations
4.1 Introduction
4.1.1 Habitat use
Individuals are located within distinct, and often specific, habitats and microhabitats
(Heatwole, 1977), so their geographic distribution, abundance and population dynamics
may be influenced by the abundance and availability of these habitat and microhabitat
types (Munday et al., 1997). This effect would be expected to be most pronounced
among habitat specialised species (Munday et al., 1997). Habitat is the resource
partitioned first by reptile and amphibian species assemblages (Schoener, 1974). This is
unsurprising considering that key behaviours, relating to thermoregulation in lizards, are
targeted toward habitat selection and afford benefits to the individual due to
maintenance of body temperature within a specific range (Huey & Slatkin, 1976).
Annual differences in habitat use due to seasonal differences in thermoregulation
requirements have been observed by a number of researchers (e.g. Christian et al., 1983;
Singh et al., 2002). This is supported by research conducted on the reptile assemblage
of Stephens Island, New Zealand by East & East (1995). East & East (1995) found that
species occupying the largest number of habitats were present at the highest
abundances, and those found in the narrowest ranges had the lowest abundances.
The suitability of habitats used by lizards is determined by a wide variety of factors
including species specific requirements for thermoregulation (Huey & Slatkin, 1976;
Spellerberg, 1976; Roughgarden et al., 1981), refuges (e.g. occurrence and state of logs)
(Webb, 1985), foraging (Gambold & Woinarski, 1993), successful reproduction (James
& Shine, 1985), and predator avoidance (Huey & Slatkin, 1976; East & East, 1995) as
well as competition (Dunham, 1980). Environmental gradients such as moisture,
69
temperature, light, humidity and soil type impact directly on individuals and their
habitat use (Christian et al., 1983; Gambold & Woinarski, 1993; Trainor & Woinarski,
1994), but also effect vegetation zones (Heatwole, 1977). Vegetation in turn is
important due to its implication in lizard habitat selection in terms of general physical
structure (Trainor & Woinarski, 1994; East & East, 1995) (e.g. extent and structure of
canopy cover) (Webb, 1985; Trainor & Woinarski, 1994) and the amount of open
versus covered ground (Twigg & Fox, 1991; Trainor & Woinarski, 1994; Singh et al.,
2002). Finally, the level of human disturbance (e.g. fire, habitat destruction) may impact
directly on lizard populations (Trainor & Woinarski, 1994; East & East, 1995), in
addition to effecting key environmental factors. The requirements of species for
different habitats and microhabitats are dynamic (Christian et al., 1983; Webb, 1985),
and differ temporally as do the scale dependent factors which determine the suitability
of sites (Trainor & Woinarski, 1994). Different sexes or life stages of the same species
may utilise different habitats due to preference (Christian et al., 1983; East & East,
1995; Singh et al., 2002), displacement through competition (Hedrick, 1993; Munday,
2001) or avoidance of intra- or interspecific predation (Christian et al., 1983;
MacCredie, 1984). Alternative explanations offered for this are to divide food resources
(Toft, 1985), or to provide for thermoregulatory requirements (Spencer & Grimmond,
1994), and this may enable more individuals of a species to inhabit a certain location
(Heatwole, 1977).
Species assemblages of lizards will also be determined by environmental variables.
Distribution of some lizard species may be correlated with certain environmental
gradients within their habitat such as moisture level or soil type, while others species are
generalised across these gradients (Trainor & Woinarski, 1994). Letnic & Fox (1997)
found lizard species in Australian assemblages to be strongly affected by changes in
vegetation structure. Vegetation structure was also important for the offshore island
lizard assemblage investigated by East & East (1995), they found all seven lizard
species present in vineland habitat, versus other habitats which did not harbour all
species. The vineland habitat had a complex thicket structure, and it was suggested that
this afforded protection from predation and intra- and interspecific aggression (East &
East, 1995). This follows the idea that habitats with greater structural diversity will have
more coexisting species (Heatwole, 1977).
70
Microhabitats may be partitioned between sympatric species (e.g. Patterson, 1992), and
within amphibian and reptile assemblages this often due to interspecific competition
(Toft, 1985). The degree of this partitioning may depend on structural heterogeneity, for
example Pianka (1977) found desert lizards partitioned microhabitat to different levels
depending on the complexity available. Patterson (1992) also found that microhabitat
distribution of the grassland skink guild studied was principally related to physical
structure of the habitat. Effects of physical structure on preference and subsequent
advantages of microhabitat use have been found for other taxa as well, e.g. tropical reef
fishes (Munday, 2001). Munday (2001) observed competitive ability for a microhabitat
increased with the fitness conferred upon a species by that microhabitat. Lizard
community research has suggested that through utilisation of specific microhabitats a
species may be shielded from the full effects of environmental variation (James, 1991).
An aim of this chapter is to indicate general trends of habitat and microhabitat use for
rainbow skinks (Lampropholis delicata) in New Zealand. Detailed investigations of
Auckland populations of rainbow skinks were combined with information gained from
populations in Tauranga and Wanganui. New Zealand populations of rainbow skinks
may differ from those in other countries and these differences might effect their
environmental requirements and interactions with other species, therefore it was
pertinent to assess their habitat use.
4.1.2 General population parameters
The population structures of lizard species are determined by a number of factors
including the space (i.e. habitats and microhabitats) available at a particular location
(Heatwole, 1977; Roughgarden et al., 1981), in addition to food, refuge and basking
areas (Heatwole, 1977; Dunham, 1980). Separate populations of the same lizard species
may show morphological, reproductive and behavioural differences (Andrews & Rand,
1974; Baker, 1979; Forsman & Shine, 1995a, b; Qualls & Shine, 1998b) especially if
71
the species which has a wide geographic distribution (Qualls & Shine, 1998b). Reasons
suggested for these differences include differing environmental conditions experienced
during development (Qualls & Shine, 1998b; Downes & Shine, 1999), and differing
levels of predation and competition pressure (Scott & Campbell, 1977). Comparisons of
island and mainland populations of black tiger snakes (Notechis ater niger) in Australia
revealed that availability of food resources explained the morphological differences in
of maximum body size, extent of sexual dimorphism and number of individuals in each
size class between the populations (Schwaner, 1985).
The general morphological characteristics (body length, mass, and tail, toe and scarring
condition) of different rainbow skink populations are compared in this chapter. As
measurements of rainbow skink populations in both Australia and the Hawaiian Islands
have been found to differ (Baker, 1979; Mather, 1986; Forsman & Shine, 1995a, b) it
was relevant to examine any differences between New Zealand with these other
populations.
4.1.3 Objectives
This chapter examines general trends of habitat and microhabitat use for rainbow skinks
in New Zealand and compares these to records for Australian and Hawaiian
populations. General morphological characteristics of selected Auckland populations
are considered, compared with conspecifics in Australia and Hawaiian populations and
where appropriate, populations of native New Zealand lizard species. New Zealand
populations of rainbow skinks may differ in habitat range from those investigated
overseas, and this will have consequences on contact with New Zealand native species.
Potential effects of overlap between lizard species are discussed.
72
4.2 Results
4.2.1 Habitat use
Rainbow skinks were observed in a variety of habitats ranging from highly modified
(glasshouses, nurseries and well maintained gardens) to scrubland (irregularly
maintained revegetated sites), rank vegetation (weedy areas beside railway sidings and
industrial sites) and lava formations in the supralittoral zone on Rangitoto Island. The
majority, (87.5%; n = 601), of individuals were utilising a refuge when observed, and
55.9 % (n = 601) were found under a canopy whether it was natural or artificial, e.g.
tree canopy, plastichouse roof.
Microhabitat use was diverse and relied heavily on substrates and refuges available at
each site (Table 4.1) (see Appendix VIII for microhabitat use of substrate and refuge
subcategories). Rainbow skinks were found on substrates ranging from natural (e.g. soil
and leaf litter) to artificial (e.g. concrete and weed mat). Refuges utilised showed the
same variety ranging from use of leaf litter and fallen logs to shade cloth and glass
bottles. Aggregations of up to eight rainbow skinks were observed using a standing
dead tree as a basking site at the Avondale site at heights of over 2 m, if disturbed they
retreated under sheets of loose bark. Differences in microhabitat use between male and
female rainbow skinks (Table 4.1) were not significant for any population (Chi-square
test: Otara substrate p > 0.2, χ2 = 6.6, df = 5; Otara refuge p > 0.3, χ
2 = 5.5, df = 5;
Massey substrate p > 0.2, χ2 = 12.1, df = 9; Massey refuge p > 0.7, χ
2 = 2.8, df = 5;
Avondale substrate p > 0.9, χ2 = 3.5, df = 9; Avondale refuge p > 0.8, χ
2 = 4.5, df = 9).
Aggregations of different life stages were commonly seen basking together and utilising
a common refuge.
Table 4.1 Percentage of rainbow skinks occupying each substrate and refuge type per site (see Table 2.2 for definitions). A dash denotes substrate and refuge types not
available at a site and sections with sample sizes considered inadequate for further examination. Beneath each initial percentage for Otara, Massey and Avondale sites
male/female splits of percentage microhabitat use are given (note that not all individuals were sexed in these populations so the sum of males and females does not equate to
the total sample size). Numbers in parentheses denote sample size.
Microhabitat use (%)
Site (Overall n:
Male n/Female n)
Otara
(135: 40/56)
Massey
(217: 51/58)
Avondale
(132: 41/33)
Swanson
(27)
Albany
(52)
Mt Wellington
(23)
Substrate type
Artificial 51.1 42.9 8.3 14.8 17.3 0.0
Male Female 52.5 35.7 52.9 32.8 9.8 6.1 - - -
Concrete - 26.3 6.8 7.4 0.0 21.7
Male Female - - 21.6 36.2 2.4 6.1 - - -
Gravel/Rock 0.0 1.8 23.5 0.0 15.4 0.0
Male Female 0.0 0.0 0.0 0.0 26.8 36.4 - - -
Growing media - 19.8 0.8 - 0.0 0.0
Male Female - - 13.7 27.6 0.0 0.0 - - -
Soil 46.7 5.5 12.1 77.8 50.0 26.1
Male Female 42.5 62.5 7.8 3.4 17.1 9.1 - - -
Litter/Vegetation 2.2 2.8 35.6 0.0 5.8 47.8
Male Female 5.0 1.8 3.9 0.0 26.8 21.2 - - -
Wood 0.0 0.9 12.9 0.0 11.5 4.3
Male Female 0.0 0.0 0.0 0.0 17.1 21.2 - - -
Table 4.1 (cont.).
Microhabitat utilisation (%)
Site (Overall n:
Male n/Female n)
Otara
(119: 39/52)
Massey
(194: 50/57)
Avondale
(119: 37/28)
Swanson
(27)
Albany
(38)
Mt Wellington
(23)
Refuge type
Artificial 81.5 91.5 14.3 60.9 34.2 21.7
Male Female 79.5 92.3 94.0 98.2 10.8 10.7 - - -
Concrete - 0.0 7.6 0.0 5.3 0.0
Male Female - - 0.0 0.0 8.1 0.0 - - -
Gravel/Rock 0.0 0.5 24.4 0.0 26.3 8.7
Male Female 0.0 0.0 0.0 0.0 35.1 28.6 - - -
Soil 0.0 0.0 0.0 21.7 7.9 0.0
Male Female 0.0 0.0 0.0 0.0 0.0 0.0 - - -
Litter/Vegetation 14.3 5.8 38.7 4.3 26.3 65.2
Male Female 17.9 7.7 4.0 0.0 21.6 32.1 - - -
Wood 4.2 2.1 15.1 13.0 0.0 4.3
Male Female 2.6 0.0 2.0 1.8 24.3 28.6 - - -
75
Copper skinks (Cyclodina aenea) were observed at Massey, Avondale and Mt
Wellington sites mainly utilising the same microhabitats as rainbow skinks. However,
rainbow skinks were always more abundant where sympatric populations occurred in
terms of overall numbers observed (e.g. three copper skinks were observed at the
Massey site versus 194 rainbow skinks captured), and in numbers utilising a common
refuge.
4.2.2 General population parameters
4.2.2.1 Weights and lengths
Adult rainbow skinks from Otara, Massey, Avondale and Mt Wellington samples were
found to have significantly different weights and snout to vent lengths (SVLs) (Kruskal-
Wallis test: weight p < 0.005; SVL p < 0.02) (Figure 4.1 & 4.2). Both measurements
were greater from the Mt Wellington sample, intermediate for the Otara and Avondale
samples, and lowest for the Massey sample. Adult rainbow skinks from Otara and
Massey samples did not have significantly different total lengths (t-test: p > 0.05, t-
value = 2.0, df = 26) (Figure 4.3), and tail length was calculated to be 155% of adult
SVL on average. Sub-adults from Massey and Avondale samples did not have
significantly different weights and SVLs (Mann-Whitney U-test: weight p > 0.2; SVL p
> 0.2) (Figure 4.4 & 4.5). Juveniles from Otara, Massey, Avondale, Swanson and
Albany samples were found to have significantly different weights and SVLs (Kruskal-
Wallis test: weight p < 0.002; SVL p < 0.01) (Figure 4.6 & 4.7).
76
Otara (111)
Massey (167)
Avondale (91)
Mt Wellington (17)
Site
0.8
1.0
1.2
1.4
1.6
1.8
2.0
Weight (g)
Figure 4.1 Weights of adult rainbow skinks. Numbers in brackets denote sample size; the box includes
values up to one standard error from the mean (represented by a line); whiskers include values up to two
standard errors from the mean; circles display outliers within four and a half standard errors of the mean.
Note that the y-axis does not begin at zero.
Otara (113)
Massey (170)
Avondale (85)
Mt Wellington (17)
Site
34
36
38
40
42
44
46
SVL (mm)
Figure 4.2 SVLs of adult rainbow skinks. Box plots set out as detailed for Figure 4.1.
77
Otara (12) Massey (16)
Site
94
96
98
100
102
104
106
108
110
Total length (mm)
Figure 4.3 Total lengths of adult rainbow skinks. Box plots set out as detailed for Figure 4.1.
Massey (24) Avondale (10)
Site
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
Weight (g)
Figure 4.4 Weights of sub-adult rainbow skinks. Box plots set out as detailed for Figure 4.1.
78
Massey (24) Avondale (11)
Site
30.5
31.0
31.5
32.0
32.5
33.0
33.5
34.0
34.5
SVL (mm)
Figure 4.5 SVLs of sub-adult rainbow skinks. Box plots set out as detailed for Figure 4.1.
Otara (22)
Massey (37)
Avondale (30)
Swanson (13)
Albany (12)
Site
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Weight (g)
Figure 4.6 Weights of juvenile rainbow skinks. Box plots set out as detailed for Figure 4.1.
79
Otara (22)
Massey (37)
Avondale (30)
Albany (12)
Swanson (13)
Site
17
18
19
20
21
22
23
24
SVL (mm)
Figure 4.7 SVLs of juvenile rainbow skinks. Box plots set out as detailed for Figure 4.1.
4.2.2.2 Tail, toe and scarring condition
Overall 59% (n = 528) of rainbow skinks captured had broken or regenerated tails. Tail
regeneration between Otara, Massey, Avondale, Swanson, Albany and Mt Wellington
samples was not significantly different (maximum likelihood ANOVA: p > 0.1, χ2 =
7.94, df = 5) (Figure 4.8). However, tail regeneration was significantly different
between life stages, with juveniles showing the lowest proportion of tail regeneration,
sub-adults an intermediate proportion, and adults the highest proportion (maximum
likelihood ANOVA: p <0.0001, χ2 = 62.73, df = 2) (Figure 4.8). No significant
difference in tail regeneration was found between sexes (maximum likelihood ANOVA:
p > 0.2, χ2 = 1.46, df = 1, n = 300 (male n =143, female n = 157)).
Overall 31% (n = 526) of rainbow skinks captured had lost toes. Significant differences
in toe loss proportion were found between Otara, Massey, Avondale, Swanson, Albany
80
and Mt Wellington samples (maximum likelihood ANOVA: p < 0.006, χ2 = 16.54, df =
5) (Figure 4.9). Sub-adult rainbow skinks from the Massey sample showed lower
amounts of toe loss than Avondale sub-adults, and adults from the Otara, Massey and
Avondale samples showed a much higher incidence of toe loss than Mt Wellington
adults (Figure 4.9). A significant difference was also found for toe loss between life
stages (maximum likelihood ANOVA: p < 0.0001, χ2 = 20.89, df = 2) (Figure 4.9), with
the same trend observed for tail regeneration evident. No significant difference in
proportions of toe loss was found between sexes (maximum likelihood ANOVA: p >
0.2, χ2 = 1.12, df = 1, n = 298 (male n = 143, female n = 155)).
No significant difference was found for scarring occurrence of adult rainbow skinks
from Otara, Massey and Avondale samples (maximum likelihood ANOVA: p > 0.9, χ2
= 0.01, df = 2, n = 184 (Otara n = 58, Massey n = 73, Avondale n = 53)). However, a
significant difference in scarring incidence was found between sexes, with males more
likely to be scarred than females (maximum likelihood ANOVA: p < 0.02, χ2 = 5.95, df
= 1) (Figure 4.10).
A significant association between tail and toe loss and occurrence of scarring was found
for adult and sub-adult rainbow skinks from Otara, Massey and Avondale (Chi-square
test: p < 0.01, χ2 = 15.92, df = 3, n = 194). More individuals than expected, should each
combination of tail and toe loss and scarring occurrence be non-related, had lost tails
and toes and had scars, and fewer individuals than expected had no tail or toe loss or
scarring incidence. Discarding individuals that were not sexed, and breaking the sample
into males and females revealed a highly significant result and the same trend for males
(Chi-square test: p < 0.001, χ2 = 20.64, df = 3, n = 90); females did not show a
significant association between the states (Chi-square test: p > 0.1, χ2 = 5.03, df = 3, n =
86).
81
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Otara Massey Avondale Swanson Albany Mt
Wellington
Site
Regeneration probability
(+/- SE)
Figure 4.8 Probability of tail regeneration for rainbow skink juveniles (dark grey), sub-adults (light grey)
and adults (white). Sample sizes: Otara: juvenile = 16, adult = 107; Massey juvenile = 35, sub-adult = 23,
adult = 155; Avondale: juvenile = 30; sub-adult = 10; adult = 88; Swanson adult = 13; Albany juvenile =
12; Mt Wellington adult = 17.
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Otara Massey Avondale Albany Swanson Mt
Wellington
Site
Loss probability
(+/- SE)
Figure 4.9 Probability of toe loss for rainbow skinks. Sample sizes: Otara: juvenile = 18; adult = 105;
Massey juvenile = 36, sub-adult = 23, adult = 153; Avondale juvenile = 30, sub-adult = 10, adult = 87;
Swanson juvenile = 13 (0.0002, SE 0.0034); Albany juvenile = 12; Mt Wellington adult = 17.
Conventions as Figure 4.8.
82
0
0.2
0.4
0.6
0.8
1
Male (84) Female (86)
Sex
Scarring probability (+/- SE)
Figure 4.10 Probability of scarring for male and female adult rainbow skinks. Numbers in brackets
denote sample size.
4.3 Discussion
4.3.1 Habitat use
Rainbow skinks were observed in a broad range of habitats, almost paralleling the
diversity of habitats used in Australia and the Hawaiian Islands (see Section 1.2.2).
Habitat use in New Zealand includes scrubland (Porter, 1985; pers. obs.), the
supralittoral zone of Rangitoto Island (Lark, 1984; pers. obs.), suburban gardens (Gill &
Whitaker, 2001; pers. obs.) and roadsides (pers. obs.). Mountainous areas were not
searched so it is unknown whether rainbow skink populations inhabit these habitats in
New Zealand as recorded in Australia and the Hawaiian Islands (Baker, 1979; Ehmann,
1992); it may be that higher altitudes would be too cold in this country. Heavily forested
areas were not surveyed, although previous sightings in New Zealand have occurred in
broadleaf forest (Table 1.2). However, broad research of lizard distribution literature for
New Zealand did not uncover records of this species in mountainous regions or areas of
83
native bush largely unmodified by humans. Hawaiian populations of rainbow skinks
have been recorded to use the perimeter of cropping areas (Quay, 1973), which were not
surveyed; although this species has well established populations in and around some
New Zealand plant nurseries (pers. obs.).
Refuge use was high among the individuals observed (87.5%), this percentage could
reflect genuinely high levels of refuge utilisation by this species due to predator
avoidance, foraging tactics, or environmental considerations (e.g. water loss, heat
stress). Alternately it could be due to disturbance caused by the sampling method, i.e.
the animals may have retreated at the sound, sight or vibrations caused by movement
around the site. Rainbow skinks were found under a canopy in 55.9% of the
observations, which may indicate a slight preference for microhabitats underneath a
canopy. However, canopy use varied widely between sites due to the presence or
absence of trees or buildings, so this result is likely to be an artefact of the data
collection; although research in Australia has found positive associations between
rainbow skink occurrence and canopy cover (Letnic & Fox, 1997).
Microhabitat use by rainbow skinks was diverse and highly opportunistic depending on
microhabitats available at the sites, i.e. concrete was unavailable as a substrate at the
Otara site but was present at all other sites (Table 4.1). No clear patterns arose from the
limited investigation undertaken; where natural substrates and refuges were available
rainbow skinks utilised them but not to the exclusion or reduction of artificial substrates
and refuges. Sites showing low percentages of use or no use of certain microhabitat
types, i.e. wood substrate at the Otara site (Table 4.1), reflect a small amount of this
substrate being available and not necessarily a preference for other microhabitats.
Although microhabitat selection has been suggested for this species by Australian
research (Forsman & Shine, 1995a). Segregation of microhabitats available at each site
by male and female rainbow skinks was not apparent, in contrast to the differential
selection between sexes suggested by (Forsman & Shine, 1995a), and refuges often
contained aggregations of rainbow skinks of different life stages.
84
The observation of rainbow skinks aggregated on a dead tree over 2 m off the ground is
interesting due to their predominantly ground dwelling habit under natural conditions in
Australia (Green, 1965). The discovery of copper skinks in the same microhabitats as
rainbow skinks is important; it is evidence that rainbow skinks come into direct contact
with a native reptile species under field conditions, which has implications regarding
potential competitive effects. In addition close contact may lead to the transmission of
parasites; however, parasites are usually adapted to one species or several that are
closely related (Maier, 1998). Although measures of abundance were not calculated in
this research, the observation of much higher abundances of rainbow versus copper
skinks where they are sympatric is compelling. It may simply be a function of body
size, rainbow skinks have a smaller body mass than copper skinks (pers. obs.), and
therefore may be supported at higher densities (Heatwole, 1977). Although, it is
interesting to note that large disparities have been observed in abundances of native
mourning geckos (Lepidodactylus lugubris) versus invasive house geckos
(Hemidactylus frenatus) in the Hawaiian Islands (Case et al., 1994). The native species
has been competitively displaced in urban and suburban areas in part due to more
efficient foraging of common geckos in this habitat (Petren & Case, 1996; Petren &
Case, 1998).
4.3.1.1 Considerations
The current investigation was carried out to assess general habitat and microhabitat use
of rainbow skinks in New Zealand. The high proportion of skinks found in refuges was
undoubtedly biased by the habitat disturbance and human pursuit of rainbow skinks for
measurement. To minimise disturbance effect on microhabitat choice, i.e. observing the
lizard during unaffected activity not in flight or hidden in a refuge, a survey method
using repeated censuses from set points would prove beneficial (as cited in Webb,
1985). The incorporation of pitfall traps into a habitat preference survey would also be
valuable to capture animals that may be using particular habitats but may not be
observed directly due to amount of cover etc. A more rigorous investigation based on
techniques of rainbow skink habitat preference examination in Australia (e.g. Mather,
1986; Graham, 1987) would allow comparison between sites and inference of habitat
85
preference. Future investigations should also note the weather conditions and time of
day each individual is observed in addition to microhabitat descriptions, due to the
effects that weather (Whitaker, 1968; Vogt & Hine, 1977; Karns, 1986; Hayes et al.,
1989) and time of day (Whitaker, 1968; Webb, 1985) can have on reptile activity.
Annual changes in habitat utilisation are also possible so studies conducted over a time
span encompassing these should be considered.
Because the investigation only included microhabitat samples where rainbow skinks
were found, and not all microhabitats available, preferences of these lizards cannot be
ascertained as habitat types were not searched in proportion to their occurrence at each
site. In addition, comparison of habitat and microhabitat use between populations
cannot be made as each site differed in habitat and microhabitat availability. However,
the results gained have allowed a general description of the breadth of habitat and
microhabitat use, and therefore an indication of habitats and microhabitats that future
surveying for rainbow skinks in New Zealand must cover.
Long term habitat and microhabitat use surveys conducted at sites where land use is
changing or where the habitat is undergoing successional changes would prove
interesting and may elucidate how robust rainbow skinks are to conditions in New
Zealand native bush. The Otara site investigated presents one opportunity to do this; it
was revegetated in approximately 1999, and has not achieved complete canopy closure.
Tracking the habitat progression from scrub to closed bush, in terms of physical and
biotic components of the habitat, and its effects on the rainbow skink population present
would be valuable. In addition formal investigation of copper skink abundances in
comparable habitats with and without sympatric rainbow skinks would clarify whether
any differences observed were disturbance or possibly rainbow skink related.
86
4.3.2 General population morphometrics
4.3.2.1 Weights and lengths
The mean SVLs of adult rainbow skinks (39 mm, 40 mm, 40 mm and 41 mm for
Massey, Otara, Avondale and Mt Wellington samples respectively) (Figure 4.2) are
equal to the SVLs for Australian populations given by many researchers (see Section
1.2.2). They also fall within the SVL range of 34 to 42 mm for adult females given by
Shine & Greer (1991), and are similar to the 42 mm recorded by Ehmann (1992).
However, they are considerably less than the 45 mm SVL recorded by Shine (1983), or
the measurements of 47 mm and over 50 mm recorded by Hutchinson et al (2001) for
Tasmania and Victoria respectively. But they are greater than the mean of 36 mm
(males) and 37 mm (females) found by Lunney et al. (1989), and 37 mm of Harris &
Johnston (1977) (although the Harris & Johnston (1977) sample contained animals that
would not be included as adults by this research). The mean SVLs found concur with
those of Baker (1979) who reported means of 39 mm, 41 mm and 42 mm for adult
females from O’ahu, Hawai’i and Kaua’i populations respectively. The sample of ten
rainbow skinks weighed by Fraser & Grigg (1984) had a mean weight of 0.94 g (±0.05)
which is closer to the mean weights found for sub-adults than adults by this research,
however the life stage or SVL of those individuals was not stated. In contrast Downes &
Hoefer (2004) report a mean mass of 1.89 g (±0.10 SE) for adult rainbow skinks which
is markedly higher than weights recorded by this study, and was not due to overly large
animals, as the mean SVL reported was 38 mm. It is also interesting to note that the
lizards are reported as very abundant in the study area sampled by that research
(Downes & Hoefer, 2004), therefore density did not appear to influence weight in that
case.
Informal observation of rainbow skink abundance at each site suggests that the mean
body weights and lengths of adults (Figure 4.1 & 4.2) follow the trend of lighter and
smaller adults at the densest population observed (Massey) through to heavier adults at
the sparsest population (Mt Wellington). This pattern is also seen for total length of
adult rainbow skinks (Figure 4.3), with larger animals in the Otara sample than from
87
Massey, although the difference is not significant. Weights and SVLs of sub-adults
from Massey and Avondale samples were not significantly different either (Figure 4.4
& 4.5), with animals from Massey having heavier and longer mean measurements than
those from Avondale. Mean juvenile weights were higher than the figure of 0.13 g
recorded for Australian juvenile rainbow skinks by Shine (1983), although this may be
due to younger animals being used for the Australian measurement. Juvenile weights
and SVLs were significantly different (Figure 4.6 & 4.7), and again the Massey sample
was smaller on average. However that is where the parallels with adult measurements
cease. A density dependent effect due to interspecific and conspecific competition for
food and space was suggested as a reason for differences between Hawaiian populations
by Baker (1979) (see Section 1.2.5), and the New Zealand populations studied may
represent a similar situation.
Rainbow skinks have long tails, 155% SVL, which is considerably longer than some
skinks native to New Zealand, i.e. copper skink, and marbled skink (Cyclodina oliveri)
which have SVL and tail approximately equal (Whitaker, 1968; pers. obs.). Rainbow
skinks escape predators by flight and caudal autonomy (Downes & Shine, 1999),
therefore long tails may assist their survival of predation attempts as tail length has been
suggested to govern a lizard’s ability to escape predation through autonomy (Congdon
et al., 1974). The more delicate physical form of rainbow skinks versus native skinks
(pers. obs.) may also assist tail shedding and easier escape through faster autonomy and
ability to penetrate smaller refuges.
4.3.2.2 Tail, toe and scarring condition
Tail loss and subsequent regeneration in lizards is an occurrence frequently attributed to
predation ( e.g. Whitaker, 1968; Porter, 1982a; Qualls & Shine, 1998a; Habgood, 2003).
When all life stages are considered, 59% of individuals examined had broken or
regenerating tails, and these percentages did not differ significantly between the
populations studied (Figure 4.8); this may be due to approximately equal predation
pressures at each site. It was found that juveniles had the lowest percentage of tail loss,
88
with intermediate percentages for sub-adults, and highest percentages for adults (Figure
4.8). This trend may be due to the higher conspicuousness of adults to predators because
of body size or longer movements, but it could also simply be a function of time
exposed to predation. Adults may be more likely to escape predation through caudal
autonomy, whereas juveniles might be missed entirely or eaten completely. In addition,
adults may experience more intraspecific aggression and mating attempts because of
their greater age and exposure time. Although, higher rates of predation on juvenile
lizards and gravid females have been suggested (Shine, 1980, 1985a). This may be the
case due to slower overall running speed of juveniles and gravid females, and
potentially greater periods spent basking in gravid females (Shine, 1980, 1985a).
Tail regeneration for rainbow skinks in Australia was found to vary significantly
between populations (55% to 71%) (Forsman & Shine, 1995a). Forsman & Shine
(1995a) found slightly more males than females with regenerated tails, but reported no
significant difference overall. High rates of tail loss are common for New Zealand
native lizards as well, with Porter (1982a) recording 84% and 76% tail regeneration
from Auckland populations of copper and ornate skinks (Cyclodina ornata). Predation
pressure and intraspecific aggression were suggested as reasons for this tail loss.
Habgood (2003) found lower percentages of tail loss for populations of copper and
moko skinks (Oligosoma moco) on the mammalian predator free Tiritiri Matangi Island,
New Zealand; at 47% and 41% respectively. However, Whitaker (1968) found high
rates (92%) of tail regeneration and loss for both Pacific gecko (Hoplodactylus
pacificus) and marbled skink on the mammal free Poor Knights Islands, New Zealand.
Although these islands are free from mammals the bird fauna contains lizard predators,
and interspecific and conspecific lizard aggression may also result in tail loss (Whitaker,
1968; Hudson, 1994). MacCredie (1984) also reported regenerated or lost tails for all
individuals of Whitaker’s skink (Cyclodina whitakeri) on Castle Rock, New Zealand
and suggested intraspecific aggression and encounters with robust skink (C. alani) as a
probable reason.
Considering all life stages and skink populations measured in this study, toe loss for
rainbow skink was 31%; in contrast to tail condition, percentage toe loss did differ
89
significantly between populations (Figure 4.9). The sample from Mt Wellington had a
much lower percentage toe loss for adults than Otara, Massey or Avondale. Informal
observations of the Mt Wellington population showed a lower density of animals than
Otara, Massey or Avondale. Should toe loss be due to intraspecific aggression a lower
abundance of animals would be expected to result in fewer encounters, and therefore
less antagonism. In this case Massey would be expected to exhibit the highest
percentage toe loss but did not. Toe condition showed the same trend as tail condition
between life stages with significant differences found (Figure 4.9), and the same reasons
for differing tail loss percentages may be given for the difference in toe loss. In addition
toe loss may occur because of disecdysis (incomplete sloughing) which can result in
bands of old epidermis being retained around the feet, over time the bands become
constricting and can result in digit loss (Frye, 1981). Older animals will have been
through more moults, and therefore would be more susceptible to accumulative
problems related to moulting than younger animals.
Scarring information was only available for sufficient numbers of adults to allow
comparison between populations and sexes, with no significant difference between
scarring percentages found between Otara, Massey and Avondale populations.
However, there was a significant difference between the sexes, with males more likely
to be scarred than females (Figure 4.10). It is possible that males are more aggressive
than females (Case et al., 1994) and therefore incur more scarring from intraspecific
fighting, which has been recorded in Australian populations of Lampropholis guichenoti
(Torr & Shine, 1996). Patterson (1992) found many animals scarred in his investigation
of the New Zealand grassland lizards the common skink (Oligosoma nigriplantare),
cryptic skink (O. inconspicuum) and McCann’s skink (O. maccanni) and suggested an
association with territoriality. In addition to high rates of autonomy among Pacific
gecko on the Poor Knights Islands, New Zealand, Whitaker (1968) also found many
individuals of this species scarred or injured. Scarring has been observed in copper and
moko skink populations, with unsuccessful predation attempts and intra- and
interspecific aggression suggested as explanations (Habgood, 2003). In the case of
rainbow skinks the scarring did not appear serious enough to have been inflicted by a
predator, resembling minor injuries that might be inflicted by conspecifics, and fights
over food items have been observed in captive and wild animals (pers. obs.).
90
Examination of overall occurrences of tail and toe loss and scarring occurrence were
undertaken to investigate any association between the states. Higher numbers of animals
bearing scars and with tail and toe loss were found than would be expected should no
association exist, and fewer animals than expected showed no evidence of injury. This
is not unexpected as individuals having higher risks of tail loss might also be expected
to loose toes or incur scars. To uncover any sex related differences samples of males
and females were tested for the association separately. Females showed no significant
difference from numbers in each injury category than expected should no association
exist. However, males showed an extremely significant result, and the same trend that
was observed for the overall sample. It would appear that male rainbow skinks are more
likely to incur all three types of damage examined than females, which may be due to
differences in movement patterns (e.g. Porter, 1982a). Porter (1982a) noted that adult
male copper and ornate skinks moved significantly more than females or juveniles.
Moving greater distances might expose individuals to more frequent predation (Porter,
1982a) and coupled with higher aggression levels in males may lead to increased
amounts of scarring, toe and tail loss. In contrast, Forsman & Shine (1995a), found
female rainbow skinks moved greater distances between subsequent captures than males
(although the difference was not significant). They also suggested that females may be
less active than males on cold days, which may leave male rainbow skinks more
vulnerable to predation due to temperature related decreases in sprint performance and
general predator avoidance.
4.3.2.3 Considerations
The significant difference in weight and SVL between populations measured in this
study may be due to genuine differences between the populations; but it may also be
due to measurement error. Mean weights differed by a maximum of 0.18 g (12% of the
heaviest mean adult body weight), which may relate to a biological difference. The
differences may also be due to collection period, with seasonal changes in weight due to
reproductive status or body condition. Samples from Otara, Massey and Avondale were
collected over a six-month period, while Mt Wellington data was collected over a
period of several weeks during winter. Since the Mt Wellington sample has the heaviest
91
mean weight it seems counter intuitive that differences were due to seasonal effect, as
winter has not been recorded as a reproductively active period for this species (Joss &
Minard, 1985). Insects would be expected to be less available in winter as well, and
investigation of body fat reserves of Niveoscincus ocellatus have shown lowest reserves
during winter (Wapstra & Swain, 2001). SVLs follow the same pattern as the weights
(maximum difference 2 mm); similarly small, significant differences were found
between Australian populations by Forsman & Shine (1995b). The large sample sizes
available for the Otara, Massey and Avondale populations may have added a level of
statistical sensitivity, which may not be relevant in biological terms (Martin & Bateson,
1993); coupled with a small sample size for Mt Wellington that may fail to encompass
the range of adult weights found in the other populations by chance. Given that mean
weights and SVLs of juvenile rainbow skinks were found to be significantly different,
with differences up to a maximum of 0.14 g (47% mean body weight of heaviest
juveniles), the magnitude of the difference it is likely to be biologically significant.
Whereas, mean juvenile SVLs differed by a maximum of 2 mm, which could be due to
measurement error, but also follows the pattern of lightest to heaviest weights.
As the majority of adult rainbow skinks captured had broken or regenerating tails only
Otara and Massey populations yielded samples considered large enough for comparison
of total length. Although the difference in means is greater than that observed for SVLs
(105 mm and 94 mm for Otara and Massey respectively) they were not found to be
significantly different from each other. This may be due to the smaller sample sizes
retracting from the power of the statistical test.
Investigations of population density, possibly using mark recapture methods, would
allow more rigorous consideration of potential density dependent differences in mean
adult weight, SVL and adult total length. Marked individuals may also be tracked,
permitting rates of tail and toe loss and scarring occurrence for each life stage and sex to
be calculated over time. A long-term study would enable the demographic make up of
the populations to be described, as long as trapping methods that did not bias the sample
to a particular life stage or sex were used. As the samples from Otara, Massey and
Avondale sites were collected with an emphasis on obtaining reproductively mature
92
specimens they were biased towards adults, and a more balanced sample would allow
differences between life stages to be explored to a greater extent.
4.3.3 Conclusions
Habitat use of rainbow skinks in New Zealand is diverse and almost imitates the
diversity seen in their native range. General microhabitat use is also diverse and highly
opportunistic with individuals making use of a range of artificial and natural substrates,
refuges and canopy cover as available. Rainbow skinks also spatially overlap with the
copper skink, a native New Zealand lizard, due to common microhabitat utilisation.
Body length for adult rainbow skinks in the New Zealand populations investigated was
the same as the majority of populations considered in Australia and the Hawaiian
Islands. Percentages of tail and toe loss were comparable to those recorded for native
New Zealand lizard populations, and varied across life stages with adults showing the
highest proportions of injury. Scarring occurrence and the association between tail and
toe loss and scarring condition was male biased, which may reflect differing levels of
aggression and predator susceptibility between sexes of rainbow skink.
93
5 Reproductive biology
5.1 Introduction
For a species to become established requirements for successful reproduction must be
met. In the case of rainbow skinks (Lampropholis delicata) this involves the standard
requirements of individuals coming into reproductive condition and encountering
sufficient numbers of conspecifics for successful mating, as well as the availability of
suitable oviposition sites. The cues most likely to be used by reptiles to come into
reproductive condition include day length, rainfall, temperature and food availability
(Davies, 1981; James & Shine, 1985; Clerke & Alford, 1993). Temperature and/or
humidity regimes are the most important abiotic factors affecting reptile embryo
development in a nest (House & Spellerberg, 1980; Bellairs, 1981; Cooper & Jackson,
1981). Temperature has been found to influence incubation period, morphology and
behaviour of juvenile lizards (Shine, 1983; Qualls & Shine, 1998b), and research of nest
site choice in Lacerta agilis has suggested that excessive tree shading may create
conditions under which nests of that species will fail (House & Spellerberg, 1980).
Lizard testes are comprised of long convoluted seminiferous tubules which enlarge
during the breeding season due to spermatogenesis, and usually decrease in volume
outside of this time (Mayhew, 1963; Porter, 1972). In lizards ova at various stages of
development tend to be present at the same time, they are encased in Graafian follicles
contained within the ovary walls (Porter, 1972). Upon rupture of the follicle and ovary
wall ova are released into the coelomic cavity where fertilisation occurs (Porter, 1972).
The fertilised egg then enters the oviduct where it is coated by different secretions,
including the eggshell, as it moves down (Porter, 1972; Davies, 1981). Due to the body
proportion constraints the paired organs of snakes and some lizards, such as the gonads,
may not lie evenly within the body cavity, with the right organ often anterior to the left
(Porter, 1972).
94
Temperate zone winters are generally unsuitable for reptile reproduction, and the
reproductive season is comparatively short due to environmental constraints (Andrews
& Rand, 1974; Wapstra & Swain, 2001). Lizards from the Australian temperate zone
show a regular pattern of seasonal reproduction with copulation occurring either early in
the breeding season or in autumn (James & Shine, 1985; Simbotwe, 1985) and
oviposition occurring from October to February (Shine, 1985b). Joss & Minard (1985)
found that the length of reproductive season for rainbow skinks in Australia increased
equally before and after the longest day when different latitudes (approximating
different temperatures) were investigated.
Past research on Australian skinks has shown the existence of trade offs between current
reproduction and future reproduction in terms of greater predation risk to gravid
females, with higher reproductive outputs presenting increased immediate risks of
predation (Shine, 1980). Gravid females experience costs associated with provisioning
developing follicles and embryos in addition to carrying the clutch, e.g. lowered
mobility and speed, and may undergo behavioural modifications to compensate (Tinkle
& Gibbons, 1977; Shine, 1980; Olsson et al., 2001). Increased periods of basking may
be required to heat a gravid female to an optimum temperature, with longer basking
times not only allowing higher body temperatures to be achieved and causing
accelerated embryonic development, and compensating for encumbrance by increasing
escape speed (Tinkle & Gibbons, 1977; Shine, 1980; Downes & Shine, 1998). If lizards
are to exploit their reproductive potential, the production of several large clutches would
be the most favourable tactic (Andrews & Rand, 1974). However, predation pressure
must also be considered; if predation is high then small clutches may be a better
strategy, and may be produced more frequently (Andrews & Rand, 1974). Experiments
conducted on Tasmanian snow skinks (Niveoscincus microlepidotus) have shown that
animals manipulated to be more fecund had lower survival rates than unmanipulated
animals (Olsson et al., 2001).
All but one of New Zealand native lizards are viviparous (Robb, 1974; Bell et al., 1983;
Robb, 1986; Cree, 1994; Higham, 1995; Gill & Whitaker, 2001), which may convey
advantages as the developing embryos are protected from adverse conditions that would
95
be experienced in the nest. These conditions include natural extremes of temperature
and humidity as well as effects of predation, parasitism, fungal growth and human
introduced toxins, e.g. pesticides (Humphreys, 1976; Spellerberg, 1976; Tinkle &
Gibbons, 1977; Bellairs, 1981; Shine, 1983; Shine, 1985a, b; Qualls & Shine, 1998a).
Viviparous females may also split reproductive effort into two time periods and
provision the embryo during gestation in addition to providing egg reserves, which
lowers the amount of effort required at one time (Speake & Thompson, 2000).
However, viviparous females will also be physically encumbered by the clutch for
longer, and should the female die at any stage of gestation, the clutch is lost as well
(Tinkle & Gibbons, 1977). As viviparous species retain embryos throughout
development they may have a lower reproductive output when compared to oviparous
species which may be able to produce multiple clutches over the same time period
(Tinkle & Gibbons, 1977). Oviparous skinks from warmer climates that produce
multiple clutches, such as the rainbow skink, have higher annual reproductive outputs
than native New Zealand skinks (Cree, 1994). Although, considering their size,
reproductive mode, and the temperate environment occupied New Zealand lizards do
not have unduly small reproductive outputs (Cree, 1994).
5.1.1 Objectives
This chapter outlines the reproductive cycle for selected Auckland populations of
rainbow skinks through the examination of reproductive organs; in addition sex ratios
and nests encountered in the field were recorded. Reproductive timing and output may
impact on population size and density, therefore effecting potential competition with
sympatric species. As rainbow skinks occur in sympatry with native New Zealand
copper skinks (Cyclodina aenea) (see Section 4.2.1) a comparison of reproductive
timing and output between these species was undertaken. In addition, reproductive data
from the present study were compared to information from Australian and Hawaiian
populations.
96
5.2 Results
The sex ratios calculated for adults from each site and for sub-adults from Massey did
not differ significantly from 1:1 (Chi-square: Otara adults p > 0.1, χ2 = 2.56, df 1;
Massey adults p > 0.6, χ2 = 0.15, df = 1; Massey sub-adults p > 0.5, χ
2 = 0.28, df = 1;
Avondale adults p > 0.8, χ2 = 0.05) (Table 5.1). Adult and sub-adult sex ratios within
sites (maximum likelihood ANOVA: p > 0.4, χ2 = 0.6, df = 1), and those for adults
between sites were not significantly different (maximum likelihood ANOVA: p > 0.4,
χ2 = 1.6, df = 2) (Table 5.1).
A total of 177 adult rainbow skink specimens were dissected for examination. In the
vast majority of animals, the right ovary or testes was anterior to the left, although a
small number examined from each site had both organs even, and in three individuals
the left organ was anterior to the right (Table 5.2).
Table 5.1 Sex ratios of each rainbow skink population considered. A dash indicates a sample size of less
than ten, which was considered insufficient for this calculation. n = sample size; M = male; F = female.
Site Adult sex ratio (n M:F) Sub-adult sex ratio (n M:F)
Otara 1:1.38 (42:58) -
Massey 1:1.08 (51:55) 1.33:1 (8:6)
Avondale 1:1.05 (43:41) -
Table 5.2 Position of reproductive organs in dissected rainbow skinks. Numbers in parentheses denote
sample size. Conventions as Table 5.1.
Site Right anterior (%) Organs even (%) Left anterior (%)
Male Female Male Female Male Female
Otara 93 (28) 97 (31) 7 (2) 3 (1) 0 (0) 0 (0)
Massey 97 (30) 86 (25) 3 (1) 7 (2) 0 (0) 7 (2)
Avondale 96 (22) 97 (31) 4 (1) 0 (0) 0 (0) 3 (1)
97
Corrected mean testis and ovary volumes were not significantly different between
Otara, Massey and Avondale populations within the months sampled (testes Kruskal
Wallis ANOVA: p > 0.06; ovaries February – Mann-Whitney U-test: p > 0.6; March to
November - Kruskal Wallis ANOVA: p > 0.2) (Figures 5.1 & 5.2). However, these
measurements differed significantly between months (testes Kruskal Wallis ANOVA: p
<< 0.001; ovaries Kruskal Wallis ANOVA: p << 0.001). Corrected mean testis volume
was greatest in February but reduced in March and April, it was low in September and
October but increased in November (Figure 5.1). Corrected mean ovary volume was
highly influenced by the presence of enlarged ova, which were present in samples from
September onwards (Figures 5.2).
The earliest yolked ova at the Otara site were detected in February, and in November
after collecting began again; these months coincide with the times of maximum
corrected mean testis volume for males (Figure 5.1). The latest yolked ova seen at this
site was in March when corrected mean testis volume had begun to decrease (Figure
5.1). The earliest yolked ova at the Massey site were detected in March, which did not
match the maximum corrected mean testis volume, occurring once it had begun to
decrease (Figure 5.1). At the Avondale site yolked ova were not detected in March or
April; and no females were captured at the site during February. Yolked ova were
observed at both Massey and Avondale sites from September to November, which
coincides with times of intermediate and increased corrected mean testis volume (Figure
5.1).
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Feb (17)
Mar (17)
Apr (15)
Sept (15)
Oct (15)
Nov (14)
Month
0
10
20
30
40
50
60
70
80
90
Mean testis volume x 100/SVL
Figure 5.1 Corrected mean testis volume for all specimens by month throughout the sampling period.
Numbers in parentheses denote sample size; the box includes values up to one standard error from the
mean (represented by a line); whiskers include values up to two standard errors from the mean; circles
display outliers within four and a half standard errors of the mean.
Figure 5.2 Corrected mean ovary volume for all specimens by month throughout the sampling period.
Conventions as Figure 5.1.
Feb (10)
Mar (13)
Apr (15)
Sept (15)
Oct (14)
Nov (17)
Month
0
20
40
60
80
100
120
140
160
180
200
220
240
Mean ovary volume x 100/SVL
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No significant differences were found for corrected mean ovary volumes between sites
in each month sampled (February – Mann-Whitney U-test: p > 0.6; March to November
- Kruskal Wallis ANOVA: p > 0.2) (Figure 5.2); so all measurements were combined
for the consideration of mean follicle diameter (Figure 5.3). Follicles were smallest
from February to April, and increased markedly in diameter between September and
October. Mean egg volume per clutch was not significantly different between sites
(Kruskal Wallis ANOVA: p > 0.6) allowing all clutch data to be combined for the
following calculations. The mean number of oviducal eggs was 4.75 (SE: 0.33; n: 12)
(range three to seven), and the mean volume for oviducal eggs was 75 mm3 (SE: 1.71;
n: 57) (range 51 to 105 mm3).
Oviducts were thin-walled for all females examined from the Otara site during
September, with the majority of animals in samples possessing thin walled oviducts
from March to April and September to October. Fleshy oviducts were found in Otara
specimens from February to April and in October. At Massey, thin-walled oviducts
were observed in all females during April, with the majority sampled having thin walled
oviducts from March to April and in October. Fleshy oviducts were found in Massey
specimens from February to March, and September to November. Oviducts were thin-
walled for the majority of Avondale specimens from March to April and in October.
Avondale females had fleshy oviducts from March to April and September to
November.
Oviducal eggs were present during November at all sites and also in February at Otara
(Figure 5.3). As clutch sizes were not significantly different between samples from each
site (Kruskal Wallis ANOVA: p > 0.9), they were combined to examine the percentage
of clutches of each size and relation of clutch size to SVL (snout to vent length) (Figure
5.4 & 5.5). Fifty percent of the clutches examined were of five eggs, 34% contained
three or four eggs, and 16% consisted of six or seven eggs (Figure 5.4). A significant
correlation between clutch size and SVL was found, with larger females tending to have
larger clutch sizes (Spearman’s rank correlation: r = 0.76; p < 0.05) (Figure 5.5).
100
Investigation of an unusual object in the intestine of an adult male rainbow skink
resulted in the discovery of an ingested juvenile that appeared to be a rainbow skink,
although some digestion had occurred and identification was carried out noting
colouration and morphology.
The number of eggs, status and location of nests observed during fieldwork is presented
in Table 5.3. Nests were observed from December to April, and contained from three to
over 30 eggs (suggesting communal nesting). Note that no eggs were removed from
these nests for hatching and subsequent identification, there identification as rainbow
skink nests has been assumed from the lizard species in the area, eggshell type, egg
morphology and colouration. Juvenile rainbow skinks were observed at every site where
this species was present, regardless of season.
Figure 5.3 Mean follicle diameter (mm) of individual specimens examined by month throughout the
sampling period. Bars indicate months in which oviducal eggs were observed; note oviducal eggs
observed for Otara only during February. Numbers in parentheses denote sample size.
Feb (9) Mar (12) Apr (13) Sept (14) Oct (14) Nov (17)
Month
0
1
2
3
4
5
Mean follicle diameter (m
m)
101
0
10
20
30
40
50
60
0 1 2 3 4 5 6 7 8
Clutch size (no. of eggs)
Percentage of clutches
Figure 5.4 Percentage of each clutch size observed for the 12 clutches examined.
0
5
10
15
20
25
30
35
40
45
50
0 1 2 3 4 5 6 7 8
Clutch size (no. of eggs)
SVL (mm)
Figure 5.5 Relationship between SVL (mm) and clutch size for the 12 female rainbow skinks sampled
with oviducal eggs. r = 0.76; p < 0.05.
102
Table 5.3 Details of rainbow skink nests encountered during fieldwork.
Date Site Number and state of eggs Microhabitat
13 Feb 03 Otara 10 unhatched Clay bank cavity, under weed
mat
17 Feb 03 Otara >30 hatched & unhatched Clay bank cavity, under weed
mat
25 Mar 03 Otara >30 unhatched eggs In rock pile
26 Mar 03 Otara 4 unhatched eggs Clay bank cavity
19 Mar 03 Avondale 1 unhatched; 2 hatched In sand/leaf litter
26 Apr 03 Swanson ~10 unhatched In clay bank
26 Apr 03 Swanson 1 unhatched; 5 hatched In clay bank, under clay clod
17 Dec 03 Wanganui 3 unhatched In carpet half buried in soil
5.3 Discussion
Australian research into the reproductive biology of rainbow skinks, and the very
similar, congeneric Lampropholis guichenoti (Clarke, 1965; Graham, 1987; Forsman &
Shine, 1995a; Downes & Hoefer, 2004), have found deviations from 1:1 for sex ratios
of samples taken throughout the year (e.g. Simbotwe, 1985; Clerke & Alford, 1993;
Forsman & Shine, 1995a). Suggested explanations for this phenomenon have been
greater ease of capturing gravid females, and the affect of air temperature on the number
of each sex active (Simbotwe, 1985; Forsman & Shine, 1995a). Although for the
present study the sample from Avondale for February was male biased, the sex ratio
over all months sampled was even. The sex ratio of copper skinks in several Tiritiri
Matangi Island, New Zealand populations was investigated by Habgood (2003), and did
not differ significantly from 1:1 overall. However, if the copper skinks from only one
habitat type were considered, female and male biased sex ratios were apparent
(Habgood, 2003). Porter (1987) investigated an Auckland population of copper skinks
and found a female biased sex ratio (1:2.7); he proposed unreliable methodology or
male biased predation due to greater movements and therefore greater predation
intensity as possible causes. This illustrates that sex ratios of captured skinks may vary
temporally and with habitat; therefore consideration of a number of samples taken over
a period of several months and in different habitat types is beneficial.
103
In the body cavity of the vast majority of rainbow skinks examined the right testis or
ovary was anterior to the left. This has also been found for copper and moko
(Oligosoma moco) skinks (Habgood, 2003), and Mayhew (1963) found that the right
testis of male granite spiny lizards (Sceloporus orcutti) was always anterior to the left.
However, the left ovary was usually anterior to the right in female granite spiny lizards
(54%) (Mayhew, 1963).
Previous research on lizard reproductive biology has found testis size to fluctuate
throughout the year, with large increases observed during the breeding season (e.g.
granite spiny lizard, Mayhew, 1963; L. guichenoti, Simbotwe, 1985; copper skinks,
Habgood, 2003). Joss & Minard (1985) found that male rainbow skinks in populations
from Sydney, Australia were not reproductive during autumn and winter, but became
reproductively active from September once spermatogenesis had begun, with a second
period of spermatogenesis in February. The present study found significant fluctuations
in corrected testes volume for all populations investigated, with the maximum mean
testis volume found in February (Figure 5.1). This contrasts with the finding of Clerke
& Alford (1993) who did not observe significant differences for testes to SVL ratios of
rainbow skinks examined from Townsville, Australia; the males seemed to constantly
be in reproductive condition. The differences between these results may be due to
methodology (Joss & Minard (1985) used weight and seminiferous tubule width instead
of volume to quantify testicular cycles), or the locations considered having different
environments.
Female rainbow skinks examined had yolked ova present in March and April which is
later in the year than reported by Joss & Minard (1985). Those authors found rainbow
skinks in Sydney populations had inactive ovaries from February to July, with growing
follicles only apparent from August to October. Therefore females either had oviducal
eggs or enlarged follicles during the reproductive season, and were reproductively
active throughout the time environmental conditions allowed (Joss & Minard, 1985).
Clerke & Alford (1993) found gravid rainbow skinks in Townsville populations from
September, when they first observed enlarged follicles, through to February. The same
trend was found for New Zealand samples, with enlarged ovarian follicles or oviducal
104
eggs present during February, October and November. This research also detected
enlarged and yolked follicles during February, and from September to November
(Figure 5.3). The relationship between yolked follicles and enlarged testes differed
depending on the month considered, with all females having yolked follicles
corresponding to times of enlarged testes, but also after testes size decreased (Figure
5.1). Simbotwe (1985) found a slight correlation between testis size and female
gravidity for L. guichenoti, however the relationship was not statistically significant.
The general trends found for Auckland rainbow skink populations are similar to those
reported for Australia, although this research found some evidence for females to be in a
reproductive state later in the breeding season. Although, it is not known whether the
yolked follicles observed in March and April continue to develop throughout winter, if
development is delayed until the following spring, or whether they are reabsorbed.
The mean clutch size observed for rainbow skinks from the present study was 4.75
eggs, which is comparable with the highest mean clutch size recorded for Australian
and Hawaiian populations of 4.4 and 4.7 eggs respectively (Baker, 1979; Forsman &
Shine, 1995b). A range of three to seven eggs was found, and is encompassed within the
range of one to eight eggs recorded for Australian populations, and one to seven eggs
recorded for Hawaiian populations (see Section 1.2.3). The reproductive output
observed was over double that found for copper skinks by Habgood (2003) (2.26
offspring; SE: 0.1) and Barwick (1959) (two offspring). In contrast to rainbow skinks,
copper skinks are viviparous and therefore do not face the constraints concerned with
oviposition into a suitable nest site, and if nests fail then a viviparous species may have
a higher annual reproductive output. The same nest site may be utilised by multiple
rainbow skinks (Clarke, 1965; Green, 1965; Shine, 1983; Ehmann, 1992; Couper &
Schneider, 1995; present study), which may decrease individual egg risk through
“safety in numbers”, but may also alert predators to the site due to high visitation rates,
and additional visual and olfactory cues during hatching. In contrast copper skinks bear
the costs of carrying each clutch for longer than they would if oviparous (Cree, 1994).
Under natural conditions rainbow skinks live a shorter time (approximately two years
(Hutchinson et al., 2001)) than copper skinks (four to five years (Porter, 1982a)). The
105
shorter life span of rainbow skinks, coupled with their higher potential annual
reproductive output may be beneficial if predation rates are high. For example, an adult
female rainbow skink removed from the population after one year may have already
produced one clutch, and therefore may halve her total reproductive output. However,
should an adult female copper skink be removed from the population after one year her
total reproductive output may have been cut by 75%.
The mean volume for oviducal eggs recorded during the present study was 75 mm3,
which is intermediate to mean volumes recorded by Forsman & Shine (1995a) of 74
mm3 and 77 mm
3 for striped and non-striped colour morphs of rainbow skinks
respectively. Oviducal eggs were present in all female rainbow skinks collected during
November which corresponds to the finding of Joss & Minard (1985) who found one or
two follicles ovulated in October or November. Females from the Otara population also
had oviducal eggs in February. This indicates one clutch of eggs per year, with the
possibility of two for the Otara population, although the latter may also indicate a late
clutch for individuals that were too immature or not in reproductive condition at the
beginning of the season. Up to three clutches per season have been recorded for
Australian populations of rainbow skinks (Ehmann, 1992). Wapstra & Swain (2001)
found that vitellogenesis of follicles of the Australian skink, Niveoscincus ocellatus,
began soon after the birth of offspring but that development was not completed until the
next breeding season. Rainbow skink females examined that had oviducal eggs often
had yolked follicles, and so the same event may be occurring within the study
populations.
Clutch size varies widely between individuals of ectothermic vertebrates within and
between species, with similar sized lizards having different clutch and neonate sizes
(Shine, 1985b). Larger reptile species usually have higher fecundities, and clutch size
has been found to be correlated with body size for skinks (Shine, 1985b; Shine & Greer,
1991). But in the case of rainbow and copper skinks this is not seen (copper skinks are
larger but have a lower annual reproductive output). This may be due to the constraints
of viviparity limiting clutch size in copper skinks (see Section 5.1). Larger rainbow
skinks tend to produce larger clutches than smaller individuals (Baker, 1979; Shine,
106
1983; present study) (Figure 5.5), as bigger females have larger body cavities allowing
the development of more eggs at once (Shine & Greer, 1991; Shine, 1992; Forsman &
Shine, 1995b). This is a common occurrence in other species as well e.g. L. guichenoti
(Simbotwe, 1985), Tasmanian snow skink (Olsson et al., 2001). However, this
correlation may only hold true for certain colour morphs within rainbow skink
populations; Forsman & Shine (1995a) found evidence of larger clutch size with larger
body size for individuals with white lateral stripes, but not for non-striped individuals.
Cree (1994) did not find significant correlations between SVL and annual reproductive
output for geckos in New Zealand or overseas, or for oviparous skinks, and found
significant negative relationship for viviparous skinks. Therefore trends appear to be
different between and within species.
Rainbow skink nests were found in a small range of protected microhabitats including
cavities in banks and under rocks (Table 5.3), a type of egg placement often observed in
species that do not borrow well (Shine, 1985b). Being small and having small eggs,
rainbow skinks would be expected to have a short incubation time as observed for other
oviparous Australian skink species, allowing them to reproduce successfully in areas
were warm seasons may be comparatively short (Shine, 1985b). Due to this the
constraint of cold temperature may not curtail their reproductive output to the same
extent as for a species with larger eggs.
Competition may occur between the neonates and juveniles of rainbow and copper
skinks when they are sympatric, as observed at Avondale and Mt Wellington sites,
which would be exacerbated if they hatch and are born at the same time. Neonates of
rainbow skinks range from 17-19 mm (Clarke, 1965; Graham, 1987), and have been
suggested to feed soon after hatching, possibly due to the lack of residual internalised
yolk (Thompson et al., 2001). The SVL recorded by Clarke (1965) and Graham (1987)
is smaller than the minimum SVL measurements for copper skinks of 21 mm and 24
mm recorded by Porter (1982a) and Habgood (2003) respectively. This size difference
may be sufficient to offset food requirements as lizards tend to partition food by size
(Toft, 1985), although the exact age of the copper skinks measured was unknown.
Juveniles of both species enter populations from February to March and so are present
107
at the same point. Studies of lizard assemblages in Australia have found that some
sympatric species breed at slightly different times of the year which may serve to reduce
interspecific competition (James & Shine, 1985). However, in the case of rainbow and
copper skinks the species have not evolved together, and so shifts in breeding season
would not be expected.
5.3.1 Considerations
The results of this section must be considered in light of small sample sizes and
incomplete sampling throughout the year. It was considered unnecessary to remove
animals throughout winter as this season has not been recorded as a reproductively
active time for rainbow skinks (Joss & Minard, 1985), and time constraints did not
allow samples to be taken throughout summer. For a more complete picture of the
breeding season of rainbow skinks in New Zealand, especially in terms of potential
multiple clutches, examination of a greater number of samples, in particular ones taken
from December to January, would be required. Investigation of nest site choice, and
conditions experienced by the eggs would assist in indicating the range of habitats
suitable for establishment of rainbow skinks in New Zealand. To determine whether
neonates and juveniles of rainbow and copper skinks place competitive pressure on each
other, research of behaviour and resource requirements must be undertaken.
Consideration of morphological aspects such as gape size and body dimensions would
also be valuable.
Predation cannot be inferred from the discovery of the ingested juvenile lizard as
scavenging may have also occurred (Cheney, 1978), and the scavenging of a dead sub-
adult by an adult under field conditions was observed by the author. However, parental
female skinks of Eumeces fasciatus prey on both eggs and neonates (Vitt & Cooper,
1986). This discovery also poses questions regarding the possibility of interspecific
scavenging or predation. The investigation of maximum food size taken by adult
rainbow skinks and the size of juvenile copper skinks in addition to observation of
mixed life stage groups of both species is pertinent.
108
Uncommonly, differences in reproductive mode may occur within the same species,
with some populations being oviparous and others viviparous, which often correlates
with the temperature experienced by each population (e.g. Lerista bougainvillii in
Australia Shine, 1985a; Qualls & Shine, 1998a). Bearing this in mind it would be
interesting if longer egg retention or viviparity appears in New Zealand populations of
rainbow skinks. In turn this could enable rainbow skinks to expand their range due to
the advantages of viviparity in colder climates (see Shine, 1985a).
5.3.2 Conclusions
The reproductive biology of rainbow skinks in New Zealand was very similar to that
reported from Australian and Hawaiian populations in terms of general testis and ovary
condition, mean egg volume and clutch size. Where rainbow and native copper skinks
are sympatric a comparatively higher annual reproductive output would be expected
from rainbow skinks due to their larger clutch sizes. As juveniles and neonates of both
species are present in populations at the same time, and utilise the same microhabitats,
an investigation of potential competition between these life stages, in addition to adults,
is pertinent.
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6 Interspecific interactions
6.1 Introduction
Behaviour may be viewed as activities resulting from a complicated interaction between
genetic and learned aspects (Maier, 1998), with interactions between individuals being
an important general behaviour (Martin & Bateson, 1993). It is an underlying
assumption in the study of animal groups that the behaviour of an individual in the
group effects the behaviour of other individuals of that group (Fentress et al., 1978). In
addition, other factors influence the behaviours exhibited by species and individuals
including predation pressure (Huey & Slatkin, 1976; East & East, 1995; Downes &
Shine, 1998) and thermoregulatory requirements (Huey & Slatkin, 1976; Roughgarden
et al., 1981; Tracy & Christian, 1986; Downes & Shine, 1998). Interactions of abiotic
and biotic factors also influence the behaviour expressed (Huey & Slatkin, 1976;
Downes & Shine, 1998). For example ambient temperature and level of solar radiation
are key environmental factors that contribute towards daily activity patterns in reptiles
(Avery, 1980), but individuals also must react to predation levels in addition to
favourable abiotic conditions when basking (Huey & Slatkin, 1976).
Intra- and interspecific competition is a widely occurring and well researched
phenomenon that effects individual behaviour (Dunham, 1980; Schoener, 1983).
Competition occurs due to common use of limited biotic and abiotic resources (Tracy &
Christian, 1986; Amarasekare, 2002) and may vary in intensity through time (Dunham,
1980; Schoener, 1983). Competition for food resources increases as resource limitations
increase, however if the resource is abundant enough to supply all animals present then
competition is lessened (Petren & Case, 1996; Maier, 1998). Lizard species may
compete for resources other than food, such as refuges and microhabitats with specific
temperature or humidity regimes e.g. basking sites (Roughgarden et al., 1981; Heap et
al., 2003). There are two main classes of competition: exploitative competition where
individuals interact indirectly and use resources that are limited and non-shareable, and
110
interference competition where individuals directly harm each other (Schoener, 1983).
Exploitative competition is the form most commonly observed in terrestrial animals
(Schoener, 1983), and requires a limited resource base (Scott & Campbell, 1977).
Levels of competition within lizard communities may be mediated by predation and
community composition as well as resource availability, with periods of low resource
availability and high demand resulting in intense competition (Dunham, 1980). For
example, the lizard Sceloporus merriami was found to exert a significant competitive
effect on the sympatric lizard species Urosaurus ornatus when drought conditions had
lowered insect abundances (Dunham, 1980). Competition is often proposed as the
reason for resource partitioning between species (Dunham, 1980) which may be spatial,
temporal or morphological (e.g. body or head size, which often effects prey size range),
and based on thermal segregation, food type or food size (Heatwole, 1977; Tracy &
Christian, 1986). Whitaker (1968) describes the partitioning of habitats and active
periods between the eight species of lizard observed on the Poor Knights Islands, New
Zealand, and suggests that the level of partitioning seen was sufficient to allow the
coexistence of this species rich assemblage. In contrast the differences in body size and
high dietry overlap have been suggested to assist in the possible competitive
displacement of the native New Zealand copper skink (Cyclodina aenea) by the larger
native ornate skink (C. ornata) (Porter, 1987).
Species competing for the same limited resource at the same time cannot coexist, and in
this situation one species will usually exhibit a behavioural shift which facilitates
coexistence (Maier, 1998); this is especially likely where species are sympatric over
large areas (Schoener, 1983). If species’ niches are extremely similar, then competition
is often strong, and one species may be excluded from a preferred site by the other; this
may also occur between conspecifics (Maier, 1998). The species or individual that is
superior may depend on the habitat, i.e. a superior competitor may successfully exclude
other individuals in a favoured environment, but not necessarily in alternative ones
(Munday, 2001). In conspecific conflicts it is often the larger animals that are dominant,
however this distinction is not as clear cut when interspecific conflicts are considered
and smaller species have been observed to dominate larger ones (Grant, 1970).
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Invasive species competing with native species may have considerable impacts, in terms
of lowering population densities and causing local extinctions of natives, without
causing overall extinction (Petren & Case, 1996). For an introduced species to establish
it must be pre-adapted to partition resources with resident species, or be different
enough in its resource requirements that it does not compete with them (Losos et al.,
1993). Introduced rainbow (Lampropholis delicata) and copper skinks occur in
sympatry and allopatry in New Zealand (see Sections 1.21, 1.31 & 4.2.1), however, it is
not known whether sympatry is sustainable in the long term.
6.1.1 Objectives
This chapter investigates the behaviour and body condition of captive rainbow and
native New Zealand copper skinks. Copper skinks were chosen as they share many
ecological and behavioural characteristics with rainbow skinks, overlapping widely in
terms of activity time and diet, and these species have been confirmed to exist in
sympatry. As interspecific interactions may affect behaviour and condition of
individuals of either species, a comparison was made between single species enclosures
and an enclosure housing both study species to examine any evidence of direct or
indirect competition between the species. Three enclosures were utilised with six copper
skinks, and thirty rainbow skinks housed in the single species enclosures, and seven
copper and twenty rainbow skinks in the enclosure containing both species.
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6.2 Results
6.2.1 Behavioural observations
6.2.1.1 Comparing focal animals in single and mixed species treatments
Behavioural states were compared between single and mixed species enclosures using
84 one hour focal animal samples. The predominant behaviour of copper skinks was
hidden (>82%, Figure 6.1), and basking for rainbow skinks (>38%, Figure 6.1). The
mean percentage of time spent in basking, foraging, hidden, moving, non-aggressive
contact and stationary behavioural states was compared for individuals of each species
in each treatment. Foraging was a relatively common behavioural state observed for
rainbow skinks, making up 17.4% and 13.4% of rainbow skink single species and
mixed species behaviours respectively (Figure 6.1). Contact between conspecifics was
relatively infrequent with no instances observed between copper skinks, and non-
aggressive contact making up 0.8% and 0.5% of the mean percentage of behavioural
states for control and experimental rainbow skink treatments (Figure 6.1); no
interspecific contact was observed.
When foraging was observed both species adopted very similar strategies, walking on
and through leaf litter and refuges using vision and olfaction to search for prey items.
Individuals of both species would also push aside small clumps of dirt with their head
and partially burrow through loose soil using their head and front feet. Prey items were
rapidly pursued when disturbed and often caught with a quick lunge; prey items of
similar sizes and types were observed to be predated by both species. Rainbow skinks
were often attracted to foraging conspecifics and attempted to catch invertebrates
disturbed by foraging activity of other animals, they were also observed to bite at and
pursue a successful conspecific, and try to take the prey item from their mouth (this
behaviour also observed in the field). Although rainbow skinks would move towards
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foraging copper skinks no incidence of a copper skink losing a prey item to a rainbow
skink was observed.
0%
20%
40%
60%
80%
100%
Ca Ca Exp Ld Exp (14) Ld (17)
Enclosure
Percentage
Figure 6.1 Mean percentage time spent in basking (black), foraging (dark grey), hidden (light grey),
moving (light blue), non-aggressive contact (dark blue) and stationary (white) behavioural states per hour
in all treatments (Ca = copper skink control; Ca Exp = copper skink experimental; Ld Exp = rainbow
skink experimental; Ld = rainbow skink control). Numbers in parentheses denote sample size; note
sample size not given for copper skink treatments (see Section 2.6.2.5).
The total time (mean minutes) each focal rainbow skink was observed basking, foraging
or hidden between rainbow skink single and mixed enclosures and was not significantly
different (Mann-Whitney U-test: basking p > 0.4; foraging p > 0.3; hidden p > 0.2)
(Figure 6.2). No basking or foraging behaviour was observed for focal copper skinks in
the control treatment, and short basking and foraging durations were observed in the
experimental treatment (Figure 6.2 A & B). Copper skinks spent a large percentage of
time hidden (Figure 6.1), and the time spent hidden was generally of longer duration for
copper skinks compared to rainbow skinks (Figure 6.2 C). In addition, single species
enclosure copper skinks spent more than twice as long hidden compared to individuals
housed with rainbow skinks (Figure 6.2 C).
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The mean duration of basking, foraging and hidden behaviour observed was not
significantly different between rainbow skink single species and mixed species
enclosures (Mann-Whitney U-test: basking p > 0.7; hidden p > 0.2; t-test: foraging p >
0.4) (Figure 6.3). No basking behaviours were observed for copper skinks in the single
species enclosure, and the mean duration of individual basking behaviours for copper
skinks in the mixed species enclosure was 60 seconds (Figure 6.3 A). Foraging
behaviours were on average 15 seconds longer for copper skinks in the mixed species
versus single species enclosures (Figure 6.3 B). Control copper skinks had a
considerably longer mean duration of hidden behaviours than those in the mixed species
enclosure (Figure 6.3 C).
The relative number of bouts per hour of basking, foraging and hidden behaviours by
copper skinks did not differ significantly between single versus mixed species
enclosures (maximum likelihood ANOVA: basking p > 0.06, χ2 = 0.06, df = 1; foraging
p > 0.4, χ2 = 0.61, df = 1; hidden p > 0.5, χ
2 = 0.28, df = 1). Similarly, significant
difference was not found in the frequency of basking and hidden behaviours for rainbow
skinks in single versus mixed species enclosures (maximum likelihood ANOVA:
basking p > 0.9, χ2 = 0.01, df = 1; hidden p > 0.2, χ
2 = 1.27, df = 1; single n = 17; mixed
n = 14). However, the frequency of foraging behaviours was significantly higher for
rainbow skinks in the mixed species enclosure (maximum likelihood ANOVA: p <
0.004, χ2 = 8.7, df: 1; single n = 17; mixed n = 14).
Frequencies of rainbow skink aggressive contact and predation events did not change
significantly when copper skinks were present (maximum likelihood ANOVA:
aggressive contact p > 0.07, χ = 3.1, df = 1; predation p > 0.06, χ2 = 3.32, df = 1; single
n = 17; mixed n = 14). Eleven aggressive conspecific contact events by rainbow skinks
were observed in this captive study; however rainbow skinks were also observed
basking communally both in the enclosures and during fieldwork.
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A) Basking
0
10
20
30
40
50
60
Ca Ca Exp Ld Exp (14) Ld (17)
Treatment
Time spent basking
(min/hr) (+/-SE)
B) Foraging
0
10
20
30
40
50
60
Ca Ca Exp Ld Exp (14) Ld (17)
Treatment
Time spent foraging
(min/hr) (+/-SE)
C) Hiding
0
10
20
30
40
50
60
Ca Ca Exp Ld Exp (14) Ld (17)
Treatment
Time spent hiding
(min/hr) (+/-SE)
Figure 6.2 Mean time spent A) basking, B) foraging or C) hidden (min/hr; mean ±SE) by focal animals
for each treatment. Conventions as Figure 6.1. Note sample size and standard error not given for copper
skink treatments (see Section 2.6.2.5).
116
A) Basking
0
50
100
150
200
250
300
350
Ca Ca Exp Ld Exp (14) Ld (17)
Treatment
Duration of basking
(s) (+/-SE)
B) Foraging
0
5
10
15
20
25
30
35
40
Ca Ca Exp Ld Exp (14) Ld (17)
Treatment
Duration of foraging
(s) (+/-SE)
C) Hiding
0
500
1000
1500
2000
2500
3000
Ca Ca Exp Ld Exp (14) Ld (17)
Treatment
Duration of hiding
(s) (+/-SE)
Figure 6.3 Mean duration (seconds; mean ± SE) of focal animals A) basking, B) foraging and C) hidden
behaviours for each treatment. Note that y-axes have different scales and copper skink treatments do not
have standard error bars (see Section 2.6.2.5). Conventions as for Figure 6.1.
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Frequencies of rainbow skink non-aggressive contact and tongue flick events, although
not significant, tended to increase when copper skinks were absent (maximum
likelihood ANOVA: non-aggressive contact p < 0.059, χ2 = 0.31, df = 1; tongue flick p
< 0.057, χ2 = 3.63, df = 1; single n = 17; mixed n = 14). Frequencies of rainbow skink
tail undulation events, although not significant, tended to increase when copper skinks
were present (maximum likelihood ANOVA: tail undulation p < 0.054, χ2 = 3.72, df =
1; single n = 17; mixed n = 14). Tail undulation was associated with rainbow skinks
approaching an occupied refuge or foraging beneath an object. No aggressive contact,
non-aggressive contact, predation or tail undulation events were observed during copper
skink observations so only tongue flick events were graphed (Figure 6.4). Copper
skinks in the single species enclosure were not observed to exhibit tongue flick
behaviour, and tongue flick events were very uncommon amongst copper skinks in the
mixed species enclosure (Figure 6.4) where they were associated with foraging
behaviour.
0
1
2
3
4
5
Ca Ca Exp Ld Exp (14) Ld (17)
Treatment
Mean tongue flick
events per hr (+/-SE)
Figure 6.4 Mean frequency of tongue flick events observed during focal animal observations for each
treatment. Note that copper skink treatments do not have standard error bars (see Section 2.6.2.5).
Conventions as for Figure 6.1.
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6.2.1.2 Comparing behavioural scans in single and mixed species treatments
All animals (copper single n = 6; copper mixed n = 7; rainbow single n = 30; rainbow
mixed n = 20) were used in 126 scan samples. No change was observed in the
occurrence of basking, foraging and hiding for copper skinks in single versus mixed
species enclosures (maximum likelihood ANOVA: basking p > 0.5, χ2 = 0.42, df = 1;
foraging p > 0.2, χ2 = 1.23, df = 1; hidden p > 0.2, χ
2 = 1.52, df = 1). Overall numbers of
foraging rainbow skinks observed during scans were similar for single versus mixed
species enclosures (maximum likelihood ANOVA: p > 0.3; χ2 = 0.87, df = 1). However,
significantly more rainbow skinks were observed basking when copper skinks were
present (maximum likelihood ANOVA: p < 0.02, χ2 = 6.4, df = 1), and more animals
were observed hiding when only rainbow skinks were present (maximum likelihood
ANOVA: p < 0.001; χ2 = 14.62, df = 1).
The proportion of animals basking, foraging and hiding during scan observations were
plotted against hours since “sunrise” in each treatment (Figure 6.5). Rainbow skinks in
the single species enclosure showed slightly higher percentages of animals hiding at the
beginning and end of the light period, and low, but relatively constant percentages of
animals foraging. Between 19% to 36% of rainbow skinks were observed basking from
one hour after “sunrise” until approximately 3.5 hours before “sunset” (Figure 6.5 C).
Rainbow skinks in the mixed species enclosure showed a lower percentage of hiding
between six and eleven hours since “sunrise” than rainbow skinks when copper skinks
were absent, and showed a larger increase in the frequency of this behaviour close to
“sunset” than the rainbow skinks in the single species enclosure (Figure 6.5 C & D).
Levels of foraging observed for the rainbow skinks in the mixed species enclosure were
low and relatively constant, and the percentage of animals basking was also comparable
between the two rainbow skink enclosures (Figure 6.5 C & D). Very little change was
observed in levels of basking, foraging and hiding for the copper skink single species
enclosure, with no incidences of basking or foraging observed during scans (Figure 6.5
A). A similar pattern was seen for copper skinks when rainbow skinks were present,
although one incidence of basking and three of foraging were observed, the
predominant behaviour detected was hidden (Figure 6.5 B).
A) B)
0
20
40
60
80
100
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Hours from "sunrise"
Individuals
per scan (%)
0
20
40
60
80
100
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Hours from "sunrise"
Individuals
per scan (%)
C) D)
0
20
40
60
80
100
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Hours from "sunrise"
Individuals
per scan (%)
0
20
40
60
80
100
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Hours from "sunrise"
Individuals
per scan (%)
Figure 6.5 Percentage individuals in each treatment observed basking (square), foraging (triangle) or hidden (circle) during scan observations plotted against hours from
“sunrise”. A) Copper skink control. B) Copper skink experimental. C) Rainbow skink control. D) Rainbow skink experimental.
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6.2.2 Body condition measurements
All animals (copper single n = 6; copper mixed n = 7; rainbow single n = 30; rainbow
mixed n = 20) were measured to track body condition from initial capture to release (9
July to 13 November 2003) (see Appendix V). The regression of log weight against log
snout to vent length (SVL) did not differ significantly between single and mixed species
enclosures for either copper (single: r = 0.32, F df (1, 9), β = -0.32; mixed: r = 0.50, F df
(1, 9), β = -0.50) or rainbow skinks (single: r = 0.15, F df (1,9), β = -0.15; mixed: r =
0.18, F df (1, 9), β = 0.18) over the course of this study (correlation coefficients test: p >
0.6). A plot of the residuals from these regressions show a similar trend for each
treatment, mean body condition increases above average (the value predicted by the
regression line represented by zero on the y-axis), drops below average and then
increases again (Figure 6.6).
121
A)
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
0.02
0.04
0.06
0.08
0 1 2 3 4 5 6 7 8 9 10
Measurement sequence
Mean body condition
(log weight vs log SVL residuals)
B)
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
0.02
0.04
0.06
0.08
0 1 2 3 4 5 6 7 8 9 10
Measurement sequence
Mean body condition (log weight vs log
SVL residuals)
Figure 6.6 Mean body condition of A) copper skink control (diamond) and experimental (square) B)
rainbow skink control (diamond) and experimental (square) treatments plotted for each measurement.
Note that measurement 0 was taken upon capture (between 9-18 July 2003), measurements 1-9 were
taken over a period of one to six days (see Appendix V), and measurement 10 was taken upon release
(between 12-13 November 2003).
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6.3 Discussion
6.3.1 Behavioural observations
Overall rainbow and native copper skinks exhibited very different behaviours (Figure
6.1). Copper skinks were mostly hidden, rarely observed basking, and potentially
foraged undercover. Porter (1982a) also found copper skinks preferred to remain
undercover, and a large amount of refuge use has also been observed for chevron skinks
(Oligosoma homalonotum) (Baling, 2003). Rainbow skinks foraged more visibly and
spent large amounts of time emerged, exhibiting basking and stationary behaviours
typical of many lizards (Avery, 1980). It was possible for this captive experiment to
have several general outcomes: no effect on either species, a negative effect for one or
both species (for example spatial displacement from basking sites) or a positive effect
for one or both species. More enclosures need to be utilised to allow replication of each
treatment and allow further consideration of these outcomes, as the animals within each
enclosure do not represent treatment replicates due to possible cage effects (Martin &
Bateson, 1993).
When visibly foraging, both study species adopted similar foraging strategies and were
observed to take similar sized prey items and types, which is not surprising considering
the generalist invertebrate diet recorded for both species (see Section 1.2 & 1.3). Shine
(1980) observed foraging in several species of lizards and found that it involved slow
movements towards a prey item prior to capture with a rapid, short pounce, and this
type of foraging strategy was also observed for rainbow and copper skinks in the
present study. Rainbow skinks were observed to crowd around conspecifics that were
actively foraging and pursue and bite conspecifics that had a food item, which was
successfully dislodged in some cases. No interspecific aggression was observed,
although copper skink foraging that caused an invertebrate to flee often attracted the
attention of rainbow skinks, and they would approach the foraging copper skink.
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Attempts by rainbow skinks to catch invertebrates disturbed by foraging copper skinks
may result in the latter losing pursued prey items, although this was not observed.
On average copper skinks in the single species enclosure spent more time hidden than
those in the mixed species enclosure (Figure 6.2 C), and the mean duration of each bout
was longer (Figure 6.3 C). The large difference between the mean duration of hidden
behaviour for copper skinks in the single versus mixed species enclosure was probably
due to observations in which copper skinks remained hidden for the entire hour in the
single species enclosure. In addition some hidden behaviours of long duration were
excluded from consideration for the copper skink mixed species enclosure, as the full
duration of behaviour was not observed due to the observation period beginning or
ending. The difference may also have been due to the larger number of animals in the
mixed species enclosure, and potentially higher disturbance levels, resulting in more
exposed activities by the copper skinks. Alternatively depletion of preferred foraging
areas may have caused copper skinks to adopt more visible foraging tactics; however
this is unlikely considering that food was added regularly. Petren & Case (1996; 1998)
found that competition between introduced house geckos (Hemidactylus frenatus) and
native Hawaiian mourning geckos (Lepidodactylus lugubris) was strongest in urban
environments and suggest that predation by domestic cats may add to the competitive
impact of the introduced species. If competition is occurring between rainbow and
copper skinks then a similar situation may be seen in New Zealand, as rainbow skinks
appear to colonise and establish in human disturbed areas easily, and this may be due in
part to reduced vulnerability to predators such as cats.
Basking and hiding were the two rainbow skink behaviours affected by housing them
with copper skinks. More rainbow skinks were observed hiding in the single species
enclosure than when copper skinks were present, which was also reflected in the
percentage of animals hiding during scans throughout the day (Figure 6.5 C). It is
possible that copper skinks dominate refuges and therefore rainbow skinks spend less
time in retreats when copper skinks are present. However, this was not supported by
observations of both species sharing refuges under natural conditions, and similar
percentages of hidden rainbow skinks were observed for mixed species and single
124
species enclosures at the beginning and end of the light period, which indicates that they
were making use of refuges. Overall more rainbow skinks were observed basking in the
mixed species enclosure versus the single species enclosure. Copper skinks foraging
under cover may displace rainbow skinks from refuges, resulting in increased basking
behaviour by rainbow skinks. Rainbow skinks in the mixed species enclosure showed
more frequent amounts of foraging behaviour than those in the single species enclosure,
which may also be due to foraging behaviour being disrupted by foraging or hidden
copper skinks. However, no direct evidence of copper skinks disturbing rainbow skinks
was observed, and rainbow skinks would bask and forage around and on top of copper
skink retreats.
Tongue flicking in lizards is associated with exposure to the scent of a known predator
(Maier, 1998; e.g. Downes & Hoefer, 2004) and is observed as part of the foraging
behaviour of some species (e.g. Whitaker, 1968). The observation of tongue flick events
in the copper skink mixed versus single species enclosure (Figure 6.4) was associated
with foraging in this treatment, during which copper skinks exhibited the behaviour.
Tail movements may also be associated with detection of a predators’ scent (Downes &
Shine, 1998; Downes & Hoefer, 2004) and the greater number of tail undulation
behaviours observed for rainbow skinks in the mixed species enclosure may mean that
copper skinks were perceived as a threat by rainbow skinks. However, in this research
tail undulation behaviour often accompanied a rainbow skink approaching an occupied
refuge or foraging beneath an object that partially concealed the skinks’ anterior. Tail
undulation expressed by rainbow skinks may instead be a general predator avoidance
strategy as suggested by Downes & Hoefer (2004) and Downes & Shine (1998) to
distract a predator from the head and body of the lizard. In the case of a partially
covered foraging lizard, or one examining a potential retreat this may be especially
beneficial. However, under the predator free conditions of the enclosures this does not
account for the behaviour, unless it is exhibited regardless of actual predator presence.
The increased level of non-aggressive contact and tongue flick events (Figure 6.4)
observed when rainbow skinks were the only species present may be due to the larger
number of conspecifics than in the mixed species enclosure. Basking areas in the single
125
species enclosure may have been utilised more often by multiple animals resulting in
higher mean frequencies of contact. Increased tongue flick events may also have been
due to the higher numbers of conspecifics as they were often directed towards an area
occupied by a conspecific. Rainbow skinks naturally live in groups and Downes &
Hoefer (2004) regularly observed wild rainbow skinks in congregations of up to 12, and
conducted experiments which showed larger groups exhibited lower levels of
antipredator behaviours. Considerable benefits may be derived from group living in this
species as predation pressures may be alleviated either through increased detection of
predators from a larger group, or through diluting the individual risk during a predation
attempt (Downes & Hoefer, 2004). In the field rainbow skinks detecting a possible
threat often run a short distance and then pause, and when in groups other individuals
responded to the flight of the initially disturbed animal by running into cover, without
appearing to detect the potential threat individually (pers. obs.).
Eleven aggressive encounters were observed between rainbow skinks in this captive
study, and potentially aggressive acts have been noted between rainbow skinks
previously (Daly, 1993). No interspecific interactions, aggressive or otherwise were
observed, and the lack of interspecific aggression suggests that should competition
occur between rainbow and copper species it may be exploitative as opposed to
interference based (e.g. Dunham, 1980). However, Heap et al. (2003) did not detect
negative impacts between captive speckled (Oligosoma infrapunctatum) and
McGregor’s skinks (Cyclodina macgregori) skinks housed together, and it may also be
that rainbow and copper skinks do not effect each other negatively or that effects are
minimal.
6.3.1.1 Considerations
Observations were necessarily conducted on captive animals as the small size and
relative secrecy of rainbow and copper skinks makes them difficult to observe reliably
for long periods of time under natural conditions. It is often the case that observations
are not feasible in the wild with weather adding to potential problems of locating and
126
observing free living animals (Martin & Bateson, 1993). Although the enclosures
contained habitats and microhabitats in which both species have been observed in the
wild (pers. obs.) and a wide variety of wild caught invertebrates, the behaviour of the
skinks may have been effected by the stress of captivity (Avery, 1980; Frye, 1981;
Martin & Bateson, 1993). Therefore differences observed between treatments may not
translate into actual differences between sympatric and allopatric lizard populations
under natural conditions (Martin & Bateson, 1993). However, the majority of events
and behavioural states that were observed were also seen during fieldwork and no
behaviours observed appeared unduly unnatural, i.e. when moving the animals did not
continuously walk the enclosure perimeter. During the experiment all individuals were
subject to the same amount of handling and observation, which would have spread the
effects of this evenly across all treatments. In addition, handling and short-term
confinement does not necessarily effect behaviour, and this may be especially true of
behaviours that are necessary for survival (McMann & Paterson, 2003), such as
basking, foraging and refuge use. However, under natural conditions individuals of all
life stages would be present in addition to predators and a wider repertoire of
behaviours may be exhibited (Martin & Bateson, 1993).
Direct behavioural observations were carried out for several reasons, including potential
difficulties of reliably capturing activity taking place in any position in the enclosure by
remote recording (Baling, 2003). In addition remote recording can seldom detect the
amount of detail and context gained from direct observation, and is less efficient than
recording behaviours at the time they occur (Martin & Bateson, 1993); although direct
observation may be more susceptible to errors in measuring behavioural durations and
rapid behaviours due to speed of recording. This research focussed on basking and
hidden behaviours, which made up large proportions of the animals time budget, and
foraging, which was considered essential for survival.
Information on the natural densities of rainbow and copper skinks in sympatric and
allopatric populations would add to the experiment design by allowing enclosures to be
stocked to natural and manipulated densities. Consideration of spatial segregation
within enclosures, and communal use of refuges, such as that carried out by Heap et al.
127
(2003) would also prove valuable, especially considering that exploitative competition
is harder to observe than interference competition (Schoener, 1983). Obviously it is
important to find a more reliable method of individually identifying copper skinks if
they were to be utilised in a similar experiment.
6.3.2 Body condition measurements
No significant differences were detected between individual copper skinks in single
versus mixed species enclosures or rainbow skinks in single versus mixed species
enclosures in terms of the mean body condition recorded. However, investigations of
captive native mourning geckos and competing introduced house geckos in the
Hawaiian Islands have elucidated possible mechanisms of competition and shown
lowered body condition, fecundity and survivorship of the native species when housed
with the introduced species (Petren & Case, 1996). In this research all treatments
resulted in increased in mean body condition upon introduction to the enclosures
(Figure 6.6), possibly due to the more favourable environmental conditions in the
enclosures (animals were collected from the field during July). A decrease in mean
body condition was then observed (Figure 6.6), which may have been due to the stress
of being in captivity and being handled for the purpose of the condition measurements.
All individuals showed similar patterns of body condition variation.
128
6.3.2.1 Considerations
The weight and SVL measurements taken may have varied, not just because of the
treatment, but due to recent successful foraging or reproductive condition, which may
effect weight measurements (Dunham, 1980); although no obviously gravid females
were used in this experiment. The experiment was necessarily short in duration, and
competition between these species, if it does occur, may not be intense enough,
especially under the experimental setup, to produce marked changes in body condition
during the course of the study.
Investigations of foraging behaviour, diet and abundance and distribution of common
prey items of sympatric rainbow and copper skinks would aid in considerations of
possible competition. Data pertaining to food resources have been termed key to the
understanding of communities by Scott & Campbell (1977), and would aid in
quantification and consideration of overall niche overlap. Ideally long term studies of
naturally sympatric and allopatric populations of both species at comparable sites would
be carried out, and additional sources of competition for resources such as mice
considered (Scott & Campbell, 1977). Removal experiments where copper and rainbow
skinks are removed from sympatric populations in comparable locations and the
remaining species are monitored concurrently with comparable allopatric populations to
assess the effects and potential reestablishment of the removed species would be an
interesting extension of the current experiment. Although, under natural conditions
competition can be extremely hard to identify due to basic population dynamics,
especially if a rare species is considered, as effects of experiments may be too small to
be detected (Schoener, 1983).
Enclosure experiments could be used to manipulate skink species composition and
density, and invertebrate densities to investigate degrees of competition, although
competition levels may be effected by enclosures (Schoener, 1983). While resource
partitioning may occur between competing species, in the case of rainbow and copper
skinks the period of time that these species have been in contact (rainbow skinks were
accidentally introduced in the early 1960s (Gill & Whitaker, 2001)) may be insufficient
129
to result in such levels of coevolution. Examination of this presents an interesting
research opportunity if morphology and behaviours of otherwise comparable allopatric
and sympatric populations of these species are considered; however knowledge of at
least the minimum number of generations in sympatry would be required.
Amarasekare (2002) proposed that when a resident consumer species is better at
exploiting a resource than an invading consumer species the potential invader will not
be able to colonise if they are only present at low levels. Should the invading species be
able to establish when rare, then the two species would not be able to coexist, and the
invading species would out compete the resident (Amarasekare, 2002). However,
Amarasekare (2002) used models solely addressing the resource under competition and
two competitors, and pointed out that in most ecosystems the processes mediating
competition would be much more complicated with predators, parasites, multiple
competitors and multiple resources. Considering the model used, if copper skinks had
been a more superior forager than rainbow skinks, rainbow skinks would not have been
able to establish. However, this model assumes that rainbow skinks were introduced at
low levels into habitats where copper skinks were found, which was not necessarily the
case.
House and mourning geckos investigated by Petren & Case (1998) coexist on a island-
wide scale with house geckos dominating in urban and suburban areas and mourning
geckos dominating in forested regions. It is possible that a similar scenario exists for
rainbow and copper skinks. Surveys to determine the habitat limits of rainbow skinks in
New Zealand could assist in verifying this hypothesis. Porter (1987) proposed that in
highly protected habitats the larger native New Zealand ornate skink may hold a
competitive advantage over the smaller native copper skink that can withstand the
predation and anthropogenic pressures of less protected areas. The same author also
suggested that sympatric populations of copper and ornate skinks may exist where
ornate skinks had decreased in abundance, and therefore exacted less competitive
pressure, but noted that such situations may not be sustainable as ornate skinks may
become locally extinct. The same may prove true for the introduced rainbow, and native
copper skinks with the smaller, possibly hardier, rainbow skinks being more able to
130
escape predation and withstand habitat modification. However, changes in habitat and
predation levels would also have to be considered as the disappearance of copper skinks
and the colonisation and establishment of rainbow skinks are not necessarily linked (e.g.
Case et al., 1994).
6.3.3 Conclusions
No direct contact was observed between rainbow and copper skinks in this experiment,
or during field observations, and individuals of each species did not appear to avoid
each other spatially when housed communally. However, both species were observed
hunting the same sizes and types of prey, and when observed to forage did so in the
same way. The mean body condition of animals in mixed versus single species
enclosures did not differ. This result could be for a number of alternative reasons: 1) no
shortage of food or other necessary resource, 2) the short duration of the experiment, or
3) resource partitioning. Interspecific competition between rainbow and copper skinks
would be expected to vary according to population density and availability of required
resources both spatially and temporally, and will require further rigorous experimental
design to clarify its potential and impacts.
131
7 General discussion
Rainbow skinks (Lampropholis delicata) are the only introduced reptile that has
successfully established outside of captivity in New Zealand (Robb, 1986; Gill &
Whitaker, 2001). They have been present in this country since an accidental
introduction from Australia in the early 1960s, and are currently well established in
several regions of the North Island (Robb, 1986; Gill & Whitaker, 2001). Experience
with other exotic species in New Zealand, for example the brushtailed possum
(Trichosurus vulpecula), indicates that even the basic ecology of a species may change
markedly out of its native environment and the species may become invasive
(Fitzgerald, 1984; Green, 1984). However to date little, if any, ecological research has
been conducted on rainbow skinks in New Zealand, and there is no indication of how
they may be effecting our native fauna.
Rainbow skinks have not yet reached their potential distribution in New Zealand and
may continue to spread inland and much further south of their current established range.
Continued spread is especially likely given their propensity to disperse with human aid
which has allowed them to colonise O’ahu, and spread throughout the main islands of
the Hawaiian chain (Baker, 1979). Human aided dispersal allows rainbow skinks to
invade new offshore islands, such as Lord Howe Island (Whitaker, 2003b), and suitable
locations disjunct from areas with established populations. Considering rainbow skinks
are robust enough to survive human disturbance in transit and in their habitat care
should be taken when revegetating and transporting building materials to areas of high
conservation interest where rainbow skinks are not desired. Of special concern are the
many northeastern offshore islands that appear to have suitable climates for rainbow
skinks, and are adjacent to mainland areas with known or potential populations. The
model used to predict potential distribution would profit from refinement based on
habitat, with assessment of which habitats are available within the predicted distribution
that rainbow skinks do and do not utilise, to hone future predicted distribution models.
132
Habitat use of rainbow skinks in New Zealand is diverse and similar to their native
range. General microhabitat use is diverse and highly opportunistic with individuals
utilising of a range of artificial and natural substrates, refuges and canopy cover as
available. Rainbow skinks come into direct contact with the native New Zealand copper
skinks due to common microhabitat utilisation where sympatric populations occur.
Long term habitat and microhabitat use surveys conducted at sites where land use is
changing, or where the habitat is undergoing successional changes, would prove
interesting and may elucidate how robust rainbow skinks are to conditions in New
Zealand native bush.
Morphological measurements investigated for selected Auckland populations of
rainbow skinks showed that adult body size was similar to the majority of records from
Australian and Hawaiian populations. Percentages of tail and toe loss were comparable
to those recorded for native New Zealand lizard populations and Australian rainbow
skink populations, and varied across life stages with adults showing the highest
proportions of injury. Scarring occurrence, and the association between tail and toe loss
and scarring condition was male biased, which may reflect differing levels of aggression
and predator susceptibility between sexes of rainbow skink. Investigations of population
density and the demographic make up of rainbow skink populations would benefit from
long-term study.
The reproductive biology of rainbow skinks in New Zealand was very similar to that
reported from Australian and Hawaiian populations. The mean reproductive output of
rainbow skinks investigated was 4.75 eggs (SE: 0.33) which is over double that found
for copper skinks by Habgood (2003) (2.26 offspring; SE: 0.1) and Barwick (1959) (two
offspring). Therefore, where rainbow and copper skinks are sympatric, a higher annual
reproductive output would be expected from rainbow skinks due to their larger clutch
sizes. For a more complete picture of the breeding cycle of rainbow skinks in New
Zealand, especially in terms of potential multiple clutches, examination of a greater
number of samples, in particular ones taken from December to January is required.
Investigation of nest site choice, and conditions experienced by the eggs may assist in
indicating the range of habitats suitable for establishment of rainbow skinks in New
133
Zealand. In addition, research on potential competition between neonates and juveniles
of rainbow and copper skinks, in terms of behaviour and resource requirements must be
undertaken.
Behavioural observations did not reveal any direct contact between rainbow and copper
skinks, and individuals of each species did not appear to avoid each other spatially when
housed together or under natural conditions. Both species were observed to target the
same sizes and types of prey, and when observed to forage, made use of the same
strategies. However, the mean body condition of rainbow and copper skinks housed
communally did not differ significantly from control animals. Ideally more enclosures
would have been utilised to allow replication of each treatment, as well as consideration
of spatial segregation within enclosures and communal use of refuges between both
species, such as carried out by Heap et al. (2003). Investigations of the foraging
behaviour and diet of sympatric rainbow and copper skinks, in addition to the
distribution and abundance of common prey items, would aid in quantifying niche
overlap and assist in consideration of potential competition. Long term studies of
naturally occurring sympatric and allopatric populations at comparable sites, with
consideration of additional sources of competition for resources would be valuable
(Scott & Campbell, 1977).
This research has begun to clarify the distribution, general morphology, reproductive
biology and behaviour of rainbow skinks in New Zealand. Sympatric populations of
rainbow skinks and native New Zealand copper skinks occur, and these species were
observed to utilise common microhabitats, forage in the same way and predate
invertebrates of the same type and size. However, initial attempts to quantify potential
competition between rainbow and copper skinks have not revealed evidence of direct or
indirect effects of communal housing. Many questions have been raised by this research
and there is much scope for future research on rainbow skinks in New Zealand.
134
8 Appendices
Appendix I
Tables of records for rainbow skink (Lampropholis delicata) sightings in New
Zealand and Australia and location details for each area predicted as suitable for
rainbow skink establishment in New Zealand.
Note: this appendix is included on the compact disc attached to the inside back cover
of the thesis.
135
Appendix II
Table of collection dates and numbers of adult rainbow skinks (Lampropholis
delicata) collected from Otara, Massey and Avondale study sites.
Note: this appendix is included on the compact disc attached to the inside back cover
of the thesis.
136
Appendix III
Environmental condition data from enclosures recorded manually and using
dataloggers.
Note: this appendix is included on the compact disc attached to the inside back cover
of the thesis.
137
Appendix IV
Focal animal pilot study data used to determine sampling regime.
Note: this appendix is included on the compact disc attached to the inside back cover
of the thesis.
138
Appendix V
Table of dates captive skinks were weighed and measured throughout the interspecific
interaction experiment.
Note: this appendix is included on the compact disc attached to the inside back cover
of the thesis.
139
Appendix VI
Table of latitude, longitude and altitude data for study sites.
Note: this appendix is included on the compact disc attached to the inside back cover
of the thesis.
140
Appendix VII
Table of temperature, relative humidity and general weather conditions experienced
during rainbow skink (Lampropholis delicata) surveys.
Note: this appendix is included on the compact disc attached to the inside back cover
of the thesis.
141
Appendix VIII
Tables of rainbow skinks (Lampropholis delicata) microhabitat use for substrate and
refuge subcategories.
Note: this appendix is included on the compact disc attached to the inside back cover
of the thesis.
142
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