Loses of biodiversity on islands

Island biodiversity• Islands have a very high level of endemism,

contributing disproportionably to their size to biodiversity

• Many classic examples of adaptive radiation and lineage diversification (Hawaiian orchids, Drosophila, honeycreepers, land snails) may be found among the world's islands.

• For the same reason that these species are endemic, they are very vulnerable to extinctions.

Islands as global hotspots of biodiversity

• Out of 25 global hotspots of biodiversity 8 are on islands: Caribbean 3, Madagascar 9, Sundaland (Malay.+Indon.)16, Wallacea 17, Philippines 18, New Caledonia 23, New Zealand 24, Polynesia-Microneasia 25

Islands as global hotspots of biodiversity

Brooks et al 2002

Natural reduction of biodiversity• Islands are highly vulnerable to natural disturbances like

hurricanes.  Spiller et al. (1998) assessed responses of spiders and lizards to disturbance caused by hurricane Lili on the Bahama Islands. 

• larger bodied animals (ie. lizards) were less vulnerable to being killed during the hurricane than spiders, though the small-bodied spider populations responded more quickly after the hurricane had passed.  

• extinction (or more properly extirpation) from islands was related to population size only when disturbance was moderate, but not when it was intense. 

• After catastrophic disturbance, recovery rates of different species were related to their dispersal abilities.  Lizards, the least capable dispersers, were absent from many suitable islands, likely a long-lasting effects of catastrophes.  

Impact of Hurricane Lilly on Islands in the Bahamas

Hurricane Lili hit these islands with a 5m storm surge and 90knot winds (Spiller 1998)

Natural reduction of biodiversity

The time scale and effect of disturbances can vary greatly (Whittaker 1998)

Natural reduction of biodiversity

Fossil record found 0-3 vertebrate population losses for 4000-8000 years prior to humans on the Galapagos Islands

Bone finds in a cave on Tonga reveal little prehuman species turnover

Despite the fact that islands are subject to natural disasters like drought, fire and cyclones, to date the fossil record has revealed no major loss of species from natural causes (Steadmann 1995)

Natural dispersal does still occur• Biodiversity on islands is the product of immigration,

extinction, and in situ speciation (in some cases). • After good dispersers colonize, the rate of new, natural

species additions may be very low. Nevertheless, it does occur. 

• The green iguana lizard Iguana iguana colonized the island of Anguilla following a series of hurricanes in the Lesser Antilles in 1995.  The storm tracks were east-northwest. 

• The iguanas are believed to have originated on the island of Guadeloupe, 300 km away Censky et al. (1998).  This lizard was previously unknown on Anguilla. 

• After the storms, a large mat of logs and uprooted trees washed ashore on Anguilla. Based on local observations, it is believed that at least 3 male and 5 female lizards were found on and around the mat on the beach on Anguilla.  One female was in a reproductive condition, making it possible that this colony of immigrants could establish on the island.

Prehistoric spread of humans• The earliest islands colonized by sea-faring peoples were

Australia, New Guinea, New Ireland, Sulawesi (Indonesia), and the Solomon Islands (earliest islands colonized are listed first).  Each of these islands were colonized at least 28,000 years ago.  Each of these islands lie in, or west of, the Melanesian Island chain.  

• Further north and east, the Micronesian Islands (Caroline Islands, Marshall Islands, Gilbert Islands and Mariana Islands) were colonized about 4000 years ago.  

• Further east and south, Fiji and New Caledonia (both in Melanesia) and Somoa and Tonga (both part of Polynesia) were colonized between 3500 and 3000 years ago.  Further east in the Polynesian chain, the Marquesas Islands, Cook Islands, Hawaiian Islands, Society (Tahiti) Islands and Easter Island were colonized in 1500-2000, 1600, 1400, 1200, and 1000-1300 years ago, respectively.  New Zealand, far south of these island groups, was among the last island groups colonized (800 years ago) owing to its extreme isolation.

Prehistoric spread of humans in PolynesiaDue to a low level of resolution among the human populations, Pacific rat mtDNA was used to reconstruct human dispersal (Matisoo-Smith et al 1998). Australia, New Guinea, New Ireland, Indonesia, and Solomon Islands at least 28,000 years ago; Micronesian Islands (Caroline Islands, Marshall Islands, Gilbert Islands and Mariana Islands) were colonized about 4000 years ago

Fiji, New Caledonia, Samoa and Tonga: 3500 and 3000. Marquesas Islands 1500-2000, Cook Islands 1600, Hawaiian Islands 1400, Society (Tahiti) Islands 1200 and Easter Island 1000-1300 New Zealand, was among the last island groups colonized (800 years ago)

Island extinction

The causes of bird extinctions on islands are due to human and non-native mammal (rats, dogs and pigs) predation.

Removal or alteration of forests through cutting, burning and introduction of non-native plants

Soil erosion through deforestation has eliminated nesting sites for burrowing seabirds

The rate of extinction after human arrival varied greatly from only 100 years in many cases (iguanas and birds) (Steadman 2002) to several thousand years, depending on island size, habitat diversity, island ruggedness and human population levels and continuity.

Modern extinctions caused by similar processes than historic, only the tools have changed (Steadman 1995)

Prehistoric extinctions

Example of Easter Islands bird species (Steadman 1995)On one island in the Marquesas the number of nesting seabirds went from 22 to 4.On one island on the Society Islands nesting birds went from 15 to 4Galapagos Islands were only settled by Europeans. Excellent fossil records show 0-3 vertebrate population losses for 4000-8000 years prior to humans, but 21-24 after human arrival

Prehistoric extinctions Human colonization of Pacific Islands resulted in large numbers

of bird extinctions, numbering ~2000 species (mainly flightless rails), or 20% of global bird diversity.

Particularly hard hit with extinction or extirpation were rails, pigeons, doves, parrots and passerines.  Seabirds (mainly shearwaters and petrels) have suffered more from extirpation than extinction.  Processes responsible for extinctions caused by prehistoric peoples apparently are similar to those today.

It is estimated that 90% of extinct bird species were inhabitants of islands

More Polynesian bird species are extinct today from human causes than are alive today, and many of the survivors have greatly reduced ranges

Bird extinctions

Decline in bird species on a Tonga Island depending on foraging height and food type

Frugivores declined very sharply with a negative effect on tree pollination

Ground feeders (7-0) became extinct caused by human and non-native mammal predation Steadman 1995)

Endemic Island Biota Extinction or EndangermentsMore than 10% of Hawaii's tremendously diverse plant

species  are extinct, and another 40% are endangered;Most of the 331 described species of endemic

Amastridae (family) snails of  Hawaii are extinct, and most of the survivors are tree-dwelling species

The land snail fauna of the Hawaiian islands once numbered more  than 750 species (>99% of which were endemic to the islands), though  most are now either extinct or endangered. 

The primary cause of species decline are introduction of nonindigenous species (e.g. carnivorous snails), and, to a lesser extent, destruction or modification of habitat (Cowie 1998).  

• Argentine ants (Iridomyrmex humilis) was introduced to Maui (Hawai'i) 25 years  ago and presently restricts the distributions of many gastropods and arthropods.• Some of those arthropods are major pollinators of endemic plant species, predators,  and flightless taxa (wolf spiders and Collembolans)(Cole et al. 1992).• The little red fire ant (Wasmannia auropunctata) was first introduced to Indefatigable (Galapagos Islands) early this century; it has since spread to 4 other islands in the archipelago.  • At least 17 of the 28 ant taxa on the Galapagos have limited distributions or abundances resulting from aggressive encounters from the little red fire ant.  It also eliminated 1 scorpion and 2 spider species (Lubin 1984).

Reasons for the high loss of biodiversity on islandsIn a meta analysis of a number of factors describing islands

(latitude, area, elevation, isolation, colonization), and comparing them with the number of bird species extinct (Blackburn & Gaston 2005)

The proportion of bird species extinct was best predicted by the isolation of an island and time since colonisation, meaning the more isolated and the earlier an island was colonized the more bird species are extinct

Hence the less new migrants arrive in an ecosystem the less its prepared to deal with them particularly if they arrive at high rates

There is also evidence that human population densities were higher on more isolated islands

The species most likely to become extinct were large bodied, flightless, ground-dwelling or ground-nesting

Causes of Island-based Species Extinctions

• Direct habitat destruction

• Introduced Species

• Overharvesting

• Depletion of food resources

Direct habitat destruction

• Direct habitat destruction associated with cutting or burning of forests for agriculture, construction, and wood extraction.  All Polynesian islands were largely or completely forested prior to man's arrival; many of these islands have only small remnants, if any, left of this original vegetation. 

• On Easter Island, loss of forest cover corresponded not only with massive species losses, but also in human misery.  It is believed that the people on this island lost their primary transportation mode (boats), and then their food supply (marine mammals) following loss of forest cover. 

• Archaeological records indicate a switch in diet from marine foods to rats prior to the civilization's demise.  Soil erosion associated with deforestation has also resulted in loss of nesting sites for some seabirds.

Introduced Species

• Animals such as feral goats, pigs, cats, dogs and especially rats (European species: Rattus rattus, Rattus norvegicus; Pacific species Rattus exulans) caused major damage to native vegetation, or competed with or preyed on native taxa. 

• Some introduced plants (Miconia in Tahiti; Psidium in Tubuai, Leucaena in Marquesas, Myrica in Hawaii) crowd out native taxa and form monospecific stands.

Overharvesting

• Many taxa had limited distributions (endemics) and thus were vulnerable not only to extirpation but also to extinction if exploited heavily. 

• Some flightless birds were almost certainly driven extinct because they evolved in the absence of mammalian predators and competitors and were unwary (=naive) of human presence and were easily captured. 

• It has been speculated that easy access to these often abundant food sources was an important factor permitting long distance sea voyages by Polynesians and Europeans.

Depletion of food resources

• In some cases, extinctions were precipitated by loss of food resources associated with destruction of habitat or introduced species. 

• For example, the New Zealand eagle Harpagornis moorei was likely dependent on moas and other large extinct birds.

• Rats (R. exulans) may have caused invertebrate declines which reduced food supplies for the extinct birds Aptornis  and Megaegotheles.

The island of Singapore• On the island of Singapore, habitat loss over the past 183 years

exceeded 95%! Corresponding with this decline was a massive documented or inferred loss of biodiversity. 

• Losses were highest for forest specialists (34-87% of taxa extinct) in taxa like butterflies, birds, fish and mammals. 

• Loss rates were lower (5-80%) for vascular plants, decapods, amphibians and reptiles. 

• More than 50% of Singapore’s residual native biodiversity is sheltered in reserves that account for only 0.25% of the island. 

• Extrapolation of these patterns using species-area relationships, reveal that 13-42% of regional populations will be lost over the coming century, and at least half of these will be losses of entire species (Brook et al. 2003)

The island of Singapore

Plant species in Tonga• On the Island of Vava’o human arrived 2600 B.P.

identified by charcoal in the sediment core indicating burning of the hardwood forest

• Increased soil erosion as documented by clay particles in sediments

• The number of frugivorous and nectarivous bird species was reduced from 19 to 6 species after human arrival

• Among the extinct species are the two largest pigeon species on Tonga

• Several large rainforest tree species with large seeds have lost their means of seed dispersal (Fall 2005)

• Several tree species are not present anymore

Lizards and shrubs

• On the Island of Menorca a frugivorous lizard became extinct after the introduction carnivourous mammals (Traveset & Riera 2005)

• The lizard consumed large amounts of the shrubs’ fruits and disperse them through their scat. They were found to be the sole disperser of seeds of a perennial shrub

• On the islands without the lizard the shrub only recruits underneath the parent plant

• This is the most likely reason why this plant is endangered

The brown tree snake (Boiga irregularis)

• It’s native in Australia and was introduced accidentally onto Guam in the 1950’s

• Overall responsible for the extinction of 3 out of 4 pelagic birds; 9 out of 13 forest birds; 3-5 out 12 reptile species on the Island of Guam.

• This snake caused the extirpation or serious reduction of most of the island's 25 resident bird species on the main island of Guam.

• Twelve species were likely extirpated as breeding residents on the main island, 8 others experienced declines of greater than or equal to 90% throughout the island or at least in the north, and 2 were kept at reduced population levels during all or much of the study.

(Wiles et al 2003)

• Declines of greater than or equal to 90% occurred rapidly, averaging just 8.9 years along three roadside survey routes combined and 1.6 years at a 100-ha forested study site (Wiles et al 2003, Rodda 1998).

New Zealand• The islands were colonized by humans only 1000-800 years ago

because of their isolation.  Endemism is high on oceanic islands in this group, though diversity is lower than on the larger (continental) islands. 

• The archipelago has extraordinary biodiversity including 75% of the world's penguins, 54% of seabirds (albatross, petrels, and shearwater), 80% of baleen whales, 50% of beaked whales and 36% of dolphins.  The islands also support many endemic species, including 35% of macroalgae, 55% of sponges, 45% of bryozoans, 20% of fish, and 30% of seabirds. 

• This tremendous diversity has resulted from the islands' range of climates (subtropical to subantarctic), isolation (oceanic to continental), latitudinal diversity, and age. 

• Over the past 200 years, 48% of the native avifauna has been rendered extinct owing to habitat destruction and introduced mammals (see below). Other factors responsible for destruction of endemic avifauna (particularly flightless birds) include overhunting and collections. 

New Zealand

Reasons why New Zealand's biodiversity still is high:

• human colonization was so recent, large tracts of evergreen forest remain• introductions were limited to the mainland areas, thus preserving biodiversity on smaller, adjacent islands • public demand for preserving species and restoring ecosystems.

New Zealand• 120 eradication programs have created 'new' habitats for the 500 or more

species threatened on the archipelago.  New Zealanders are also trying to rid the archipelago of ornamental plants introduced by British colonists 'acclimatization societies'  

• Reforestation programs aimed at restoring native vegetation and habitats have proven successful, and in some cases have helped endangered animals recover. 

• For example, the black robin (Petroica traversi) numbered only 9 individuals in 1975; the 7 (2 breeding pairs) birds were captured in 1976-1977 and moved from its degraded habitat on Little Mangere Island to Mangere and later to South East Islands.  These larger islands had much better (and improving) forest conditions.  The species was on the brink of extinction (10-15 individuals) for 8 more years before eggs were cross-fostered with Chatham Island Tits, which increased production of black robin fledglings. In 1992 the species totalled 120 birds.

• Helicopter-dispersed rodenticide eliminated rats from Red Mercury Island after the 20 resident tuataras were removed.  These individuals have been in a captive-breeding program, and will soon be re-established on the rat-free island. Two rare skinks will also be reintroduced to the island. Programs of ecological restoration and habitat rehabilitation are ongoing on many of the nation's islands and are critical to survival of many endemic plants and animals.

• Captive breeding programs are presently helping two endangered flightless birds: the nocturnal parrot Kakapo (Strigops habroptilus), of which 50 individuals remain, and the gallinule Takahe (Porphyrio mantelli), of which 150 individuals remain (Clout and Craig 1994).  These species were both thought extinct before small populations were found. 

Chatham Island black robin tuatara

kakapo takahe

Kakapo example (Elliot 2001)

It’s a flightless, nocturnal, herbivorous, lek breeder that breeds only every 2-5 years and leaves the eggs unattended for long timesWhile protected from visual predators, predators hunting by smell can are a threat. Rats and dogs were introduced by the Polynesians and Europeans introduced rats, cats, mustelids (ferrets and weasels); all prey on KakaposAdditionally the native forest is reduced in large areas, but the main problem is predationBy the 1970 only two populations on Stewart Island and in the Northern Fjordland remained

The Kakapo (Strigops habrotilus) is a large parrot (1.5-4kg) endemic to New Zealand and on of the worlds rarest birds (62 individuals)

Due to high mortality of adult parrots caused by cats, all animals were translocated to three relatively predator free islands in the 1980s-1990sAdult survival was between 98-99%, but only three chicks were reared until 1995, leading to a much more intensive and intrusive management of the speciesAs the Kakapo nesting seem to coincide with large crops of fruits and seeds every 3-4 years, supplementary feeding was used to increase the breeding frequency. Feeding also reduced the amount of time the female was away from the eggs.A total of 15 chicks have fledged since 1995

In order to prevent any further loss of eggs or chicks to predators all nests were continuously monitored and traps and deterrents were used to remove predators

Between 1981-1994 43% of the nestlings were eaten by rats. Since intensified protection the overall chick mortality has dropped from 75% to 29%

Potentially infertile males are removed to other islandsThe last remaining male of a different island population was

moved to an island with several femalesEggs or chicks which were considered failing were removed from

the nests and hand reared and later released

Vertebrate invaders in New Zealand

Invader controlRemoval of invasive species is an expensive and labour intensive approachLow level control efforts may help protect select native species, current eradication methods,limited conservation funds, and the potential negative non-target impacts of sustained control efforts all favour an intense eradication effort, rather than a sustained control program

Eradication of feral pigs from Santiago Island in the Galapagos Archipelago, Ecuador, which is the largest insular pig removal to dateUsing a combination of ground hunting and poisoning, over 18,000 pigs were removed during this 30-year eradication campaign

Feral GoatsGoats were introduced to many islands by sailors in order to

establish food sources (Saint Helena, Juan Ferndandez, Hawaii)Island biotas mostly evolved largely without large mammalian

herbivours, and therefore where ill adaptedIntroduced goats, changed the composition of plant communities,

caused extinctions and accelerated soil erosionGoats are identified as the primary threat to 26% of threatened

insular plant species (IUCN)They can be the sole reason or a contributing factor for island

extinctionsFauna recovery after goat removal is often dramatic even with long-

standing goat populations (for example Pinta and Santiago Islands Galapagos) (Campell & Donlan 2005)

The use of GIS aided hunting techniques and Judas Goats greatly increased the efficency and reduced the costs of these programs

Campbell & Donlan 2005

Campbell & Donlan 2005

Conservation strategiesNew Zealand only has three native mammals, bats, as it has been separated from Gondwana for at least 75million years (Atkinson 2001)Native animals and plants are not adapted to the pressure from mammalian predators and herbivores respectively

11 species of Moas and the large Haasts eagle became extinctOriginal restoration efforts on the smaller islands. It was immediately realized that mammal eradication is a key part36 near shore islands and 16 offshore islands have been cleared of mammals

There are also 18 ‘mainland islands’ of a total area of 28,360ha created were invasive animals and plants are controlled in order protect natives

Atkinson 2001

Summary

Large losses of biodiversity have already occurred on islands

Many species are endangered and threatened with extinction

Key point for conservation is the removal of invasive species

Better and more efficient tools are available for the removal of mammalian predators and herbivores

There are several success stories of conservation and restoration of island habitats

ReferencesBiological Conservation 99 (1) issue on Introduced pest species and biodiversity conservation in New Zealand several

good articlesWhitaker RJ 1998. Island Biogeography, Ecology, Evolution, and Conservation, Oxford University Press. BOOKCensky, E.J. et al. 1998. Over-water dispersal of lizards due to hurricanes.  Nature 395:556.  Brooks TM, Mittermeier RA, Mittermeier CG, et al. Habitat loss and extinction in the hotspots of biodiversity 

CONSERVATION BIOLOGY 16 (4): 909-923 2002 Spiller DA, Losos JB, Schoener TW Impact of a catastrophic hurricane on island populations SCIENCE 281 (5377):

695-697 1998 Steadman DW, Pregill GK, Burley DV  PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE

UNITED STATES OF AMERICA 99 (6): 3673-3677 2002 Elliott GP, Merton DV, Jansen PW Intensive management of a critically endangered species: the kakapo 

BIOLOGICAL CONSERVATION 99 (1): 121-133 2001 STEADMAN DW PREHISTORIC EXTINCTIONS OF PACIFIC ISLAND BIRDS - BIODIVERSITY MEETS

ZOOARCHAEOLOGY  SCIENCE 267 (5201): 1123-1131 1995 Saunders A, Norton DA Ecological restoration at Mainland Islands in New Zealand  BIOLOGICAL CONSERVATION 99

(1): 109-119 2001 Campbell K, Donlan CJ Feral goat eradications on islands  CONSERVATION BIOLOGY 19 (5): 1362-1374 2005 Blackburn & Gaston 2005 Biological invasions and the loss of birds on islands; insights into the idiosyncrasies of

extinction. Sax DF, Stachowicz JJ, Gaines SD, (eds) Species invasions; insights into ecology, evolution, and biogeography BOOK

Fall PL Vegetation change in the coastal-lowland rainforest at Avai'o'vuna Swamp, Vava'u, Kingdom of Tonga QUATERNARY RESEARCH 64 (3): 451-459 2005

Traveset A, Riera N Disruption of a plant-lizard seed dispersal system and its ecological effects on a threatened endemic plant in the Balearic Islands  CONSERVATION BIOLOGY 19 (2): 421-431 2005

Cowie, R.H. 1998. Patterns of introduction of non-indigenous non-marine snails   and slugs in the Hawaiian Islands. Biodiversity and Conservation 7:349-368.

Cole, F.R., A.C. Medeiros, L.L. Loope and W.W. Zuehlke. 1992.  Effects of the Argentine ant on arthropod fauna of Hawaiian high-elevation shrubland. Ecology 13:1313-1322.

Lubin, Y.D. 1984. Changes in the native fauna of the Galapagos Islands following invasion by the little red fire ant, Wasmannia auropunctata. Biological Journal of the Linnean Society 21:229-242. Brook BW, Sodhi NS, Ng PKL Catastrophic extinctions follow deforestation in Singapore  NATURE 424 (6947): 420-423 JUL 24 2003 Wiles GJ, Bart J, Beck RE, et al.Impacts of the brown tree snake: Patterns of decline and species persistence in Guam's avifauna CONSERVATION BIOLOGY 17 (5): 1350-1360 OCT 2003 Atkinson IAEIntroduced mammals and models for restoration BIOLOGICAL CONSERVATION 99 (1): 81-96 MAY 2001