Habitat characteristics and bird species richness relationships within five sites in southern Tenerife: implications for endemic extinction.

Abstract

Island dwelling endemic species are more specialised in their habitat selection due to increased niche competition and limited range. When faced with serious habitat loss, endemic species are at greater risk of extinction than non-endemics. The Pinus canariensis forest of Tenerife is home to a number of bird species, one of which is classed as Near Threatened by the IUCN red list and happens to be an endemic species; the blue chaffinch, Fringella teydea teydea. Historically this bird has become increasingly endangered due to degradation and decline of its natural habitat. Using line transect distance sampling in five diverse habitat locations across southern Tenerife, bird species abundance was recorded across three days in addition to performing habitat surveys of key habitat characteristics such as percentage ground cover, plant species abundance and a biomass measure. This was used to determine any correlations between bird species abundance and habitat characteristics, with particular interest in correlations between endemics. Findings from this study determined that increasing biomass positively correlated with bird species richness. There was a significant positive correlation between plant species richness and bird species richness in addition to significant positive correlations between endemic bird species, increasing biomass and overall bird species richness.

Introduction

Since the 1600’s over 60% of species extinctions have happened within island ecosystems (Algar & Losos 2011). As we continue through the Halocene, which has become known as the sixth great extinction event (Chivian & Bernstein 2008) extinction rates are expected to increase.

The island of Tenerife has eight endemic bird species across varying habitats, such as the Pinus canariensis forest (Delgado et al. 2008). Island dwelling endemic species are more specialised in their habitat selection due to increased niche competition and limited range (Owen & Bennett 2003 and Boyer & Jetz 2014) consequently they suffer significantly under ecological stress such as habitat disruption and predation (MacArthur & Wilson 1967). As a result endemic species are at greater risk of extinction than non-endemics (Zhai et al. and Oppel et al. and Cimadom et al. 2014). Habitat preference, habitat characteristics and species abundance correlations can provide understanding into the impacts of such ecological stressors (Granier et al. 2014) and help determine the best methods of conserving and protecting endemic species within their preferred environments. This too can provide insight as to any subsequent impacts such conservation measures may have on other endemic species that occupy/competing for the same niche (Lange et al. 2014).

Ordinarily in mainland terrestrial habitats, when a species is in competition for a niche, the unsuccessful species is either forced to adapt into another niche or face extinction (Mackenzie et al. 2006). Within island dynamics of niche competition, due to occupying such a limited range; endemic species experience what is known as ecological release. This is the release of habitat preferences commonly occurring within a species when occupying a mainland habitat, which when faced with over competition for those same habitat preferences within an island habitat; is forced to adapt into alternative habitats/niches (Bolnick et al. 2010). This was demonstrated in Guillaumet & Leotard (2015) investigation into the effects of interspecific competition between Galerida cristata and Galerida theklae which found that due to the pressures applied to Galerida cristata from interspecific competition, they changed their habitat preference from occupying dunes and crop fields, to occupying stony hillsides and rocky slopes.

On Tenerife, approximately 45% of its terrestrial environment is protected in an effort to conserve its native wildlife (OAPN 2009). Conservation efforts are in place to manage catastrophic events such as forest fires (Garcia et al. 2010), however not enough is known about the habitat preferences of endemic bird species to efficiently establish practices aimed at increasing and sustaining population levels of endemic species via means of preferential habitat maintenance or protection. Such an understanding could underpin better conservation efforts to increase population levels of the Fringilla teydea teydea and protection of the species in addition to other endemic species within Tenerife.

From the research conducted on habitat preference of F. t. teydea, it was found that during the winter months of nonbreeding; food preference changes cause F. t. teydea to forage in mainly low height ground shrubs with particular preference to the Adenocarpu sp. and Myrica faya (Garcia-del-Rey & Cresswell 2005 and Garcia et al. 2009). In addition to its change in habitat preference during the nonbreeding months it was found that changing densities within the Pinus canariensis forest also affected species abundance and habitat preference of this species causing a decline in numbers throughout regions of high tree density (Garcia et al. 2010).

Most of the research conducted on habitat preferences of endemic bird species on Tenerife focuses on the Fringilla t. teydea due to its current IUCN threat level of “near threatened” (Birdlife international 2012). Though the species abundance of the F.t. teydea on Tenerife has been assessed as common and stable (Garcia-del-Rey & Cresswell 2005) in neighbouring Gran Canaria the Fringilla teydea polatzeki has been assessed as Endangered (Garcia et al. 2013).

Aim

To determine if bird species richness is impact upon by habitat characteristics. In addition, to determine if endemic bird species are affected by the same habitat characteristics?

From this it can be determined if current land management practices are effectively protecting endemic bird species in the correct habitats.

Objectives

To achieve this aim, the following objectives were considered:

Obtain species richness data of bird species, biomass and species richness data of plant species within five habitats across South Tenerife.Determine any correlations between habitat characteristics, bird species richness and endemic bird species; that could identify habitat preferences

Method

Location

The following five sites were selected for their diverse habitats in varying degrees of vegetation;

The Pinus canariensis forest: a high altitude, coniferous habitat with signs of fire damage and limited/patchy ground cover or shrubbery.

The laurel forest: a mid-altitude, evergreen habitat with abundant lichen and thick ground cover/shrubbery.

Mediterranean scrubland (Arona): a low altitude, succulent/cacti abundant habitat with course/patchy grasses and large rock formations.

Mount Teide: a high altitude, shrub dominant habitat with dry, rocky terrain.

Los Cristianos: a low altitude, urban coastline development of artificial green spaces and abundant tourist traffic.

Experimental protocol

A minimum of 200 bird samples and 200 habitat samples were the target figures to be achieved in this study to provide adequate data entries for valid and accurate statistical analysis. A distance sampling method was used along a 4 km transect over four hours in each site, performing a habitat survey every 100 m. Sampling were taken over 37 points across the entirety of the transect line for all birds seen, recording number of individuals spotted, its position in the vegetation, the species of bird and its distance from the viewer. Each observer was equipped with the binoculars and identification chart to help determine the bird species being observed. In addition to this whenever a bird was seen, a laser rangefinder was used to measure the birds perpendicular distance from the viewer along the transect line. The transect line itself was formed along known footpaths due to terrain limitations and safety of the observers. Each line was marked within a GPS to ensure an accurate measure of distance was kept. The habitat survey was conducted every hundred metres using a 10 m x 10 m quadrate to observe and record percentage ground cover vegetation, number of plant species and a girth measurement in metres of the three largest plants which were then averaged to use as a biomass measure.

In total twelve researchers were divided across two habitats per day, with three researchers conducting bird surveys and three researchers conducting habitat surveys behind the birds researchers at a delayed pace to minimise disruption to birds in the area.

Results

The results gathered have been statistically explored to determine the following mean frequency counts per recorded variable per habitat. The following habitat codes are used to identify each habitat:

1 = The Pinus canariensis forest2 = The Laurel forest3 = The Mediterranean scrubland (Arona)4 = Mount Teide5 = Los Cristianos

Habitat CodeVariable 1 2 3 4 5Bird Species Count

0.730 ± 0.902 P= 0.000 n=37

1.568 ± 1.041 P= 0.003 n= 37

0.865 ± 1.041 P= 0.000 n= 37

0.556 ± 0.773 P= 0.000 n= 36

1.129 ± 1.057 P= 0.000 n= 31

Endemic Bird Count

0.324 ± 0.530 P= 0.000 n= 37

0.378 ± 0.491 P= 0.000 n= 37

0.189 ± 0.397 P= 0.000 n= 37

0.278 ± 0.454 P= 0.000 n= 36

0.194 ± 0.402 P= 0.000 n= 31

Individual Bird Count

1.213 ± 1.750 P= 0.000 n= 37

2.081 ± 1.722 P= 0.000 n= 37

2.000 ± 3.472 P= 0.000 n= 37

0.389 ± 1.149 P= 0.000 n= 36

2.452 ± 3.064 P= 0.000 n= 31

% Ground Cover

8.486 ± 8.325 P= 0.000 n= 37

21.284 ± 20.221 P= 0.000 n= 37

32.568 ± 22.310 P= 0.001 n= 37

32.361 ± 20.870 P= 0.011 n= 36

17.355 ± 27.730 P= 0.000 n= 31

Plant Species Count

3.216 ± 1.988 P= 0.001 n= 37

12.405 ± 4.220 P= 0.008 n= 37

7.541 ± 2.864 P= 0.141 n= 37

3.167 ± 1.363 P= 0.021 n= 36

4.290 ± 2.673 P= 0.020 n= 31

Average Girth

1.032 ± 0.311 P= 0.168 n= 37

0.938 ± 0.311 P= 0.296 n= 37

0.275 ± 0.180 P= 0.065 n= 37

0.157 ± 0.192 P= 0.000 n= 36

0.841 ± 0.737 P= 0.005 n= 37

Table 1. Mean frequency count per variable for each habitat. P = Shapiro-Wilks normality P value

Table 1 identifies initial observations of highest bird species count (species richness) in the Laurel forest and lowest species richness on Mount Teide. The highest endemic bird count was within the Laurel forest and the lowest was within the Mediterranean scrubland of Arona. The highest individual bird count was within the Laurel forest and lowest individual bird count on Mount Teide. The highest percentage ground cover was within the Mediterranean scrubland of Arona and the lowest was within the Pinus canariensis forest. The highest plant species count was within the Laurel forest and the lowest was within Mount Teide. The highest average girth (Biomass) was within the Pinus canariensis forest and the lowest was within Mount Teide. Due to high standard deviation as a result of a high zero data entries (as a result of no bird sightings or no plant growth) more analysis is required before accurate conclusions can be gained from this data.

Habitat CodeBirds observed 1 2 3 4 5

No. Endemic Species 3 2 4 3 2

No. Species 6 5 10 6 9

No. Species specific to habitat 3 1 4 2 2Table 2. Total endemic bird species count per habitat, total bird species count per habitat and total identified bird species specific to the habitat they were observed in.

Table 2 shows that the Mediterranean scrubland of Arona had the highest total species richness with the highest total endemic species and species only occurring within that habitat. Comparatively to table 1, the Mediterranean

scrubland is more biodiverse however the frequency in which the birds identified occurred, was fewer but in larger number; thus the average was reduced as per the results demonstrated in table 1. The laurel forest had the fewest number of species and least number of endemics.

A Kruskal-wallis test identified that there is a significant difference in bird species richness between habitats by producing a P value of >0.000. This means that the null hypothesis of “there is no difference in number of bird species

Figure 1. Average bird species count across each habitat

between habitats” should be rejected and the Ha of “there is a difference in the number of bird species between habitats” should be accepted. Figure 1 shows the Laurel forest has the highest average bird species, which supports the alternative hypothesis.

A Spearman’s rank correlation was performed to determine any relationships between bird species count (species richness), endemic bird species and the measured habitat characteristics. The following significant positive coefficient correlations were produced:

Bird species richness - Plant species count (species richness) P = 0.279- Average girth (Biomass) P = 0.353

Endemic bird species- Bird species count (species richness) P = 0.590- Individual bird count P = 0.582- Average girth (biomass) P = 0.251

The findings from the correlation analysis show that as plant species richness increases, so too does bird species richness. This is shown in figure 3. In addition, as bird species richness increases, so too does endemic bird species richness. The positive correlation between average girth (biomass) and both overall bird species richness and endemic species richness, indicates that as biomass increases, so too does bird species richness and endemic bird species richness. This is shown in figure 2 for bird species richness. Though there was a small indication of a correlation between bird species richness and percentage ground cover, it was of enough significance to be a confirmed coefficient correlation.

Discussion:

Findings from this investigation have identified that across the island of Tenerife, specifically with in the habitats tested; the null hypothesis stating that “there is no relationship between bird species richness, plant species richness and biomass” should be rejected and the alternative hypothesis (Ha) of “there is a relationship between bird species richness, plant species richness and biomass” should be accepted. The observed correlations means that as biomass and plant species richness increases so too does bird species richness. Though endemic bird species do not have a significant correlation with habitat characteristics other than biomass abundance, the significant positive correlation with bird species richness is an indication that investment in overall bird species richness conservation is of benefit to endemic bird species as well.

Of the bird species observed, to bird species were present in all or most of the tested habitats. The African blue tit and Canary island Canary were present in multiple habitats demonstrating a robust niche selection. However the species with the most limited niche selection and subsequently restricted range, was the Blue Chaffinch which only occurred in the pine forest. These findings support the theory of ecological release (Bolnick et al. 2010) identifying that both the African blue tit and Canary island Canary have alleviated interspecific competition for niche selection by adapting to occupy a broader range of niches. On the mainland the African blue to is found predominantly

Figure 2. Bird species count (Species richness) across all average girth (m) Figure 3. Bird species count (Species richness) across plant species count (plant species richness)

within dense forest vegetation, however within Tenerife it was identified within four comparatively different habitats.

The absence of the laurel pigeon within the assessment of the Laurel Forest is of significant interest. Its absence could be attributed to a number of factors outlined by this study. Though the total number of endemic species recorded within the Laurel Forest was two, there was a significant number of nonendemic species which could be an indication that the laurel pigeon may have been dislodged from its niche by interspecific competition or it may have experienced ecological release. Recommendations for conservation efforts towards the protection of the laurel pigeon include increased plant species richness and biomass to encourage an increase of bird species richness which should in turn increase endemic species richness. The same conservation efforts could be applied to the conservation of the blue chaffinch to ensure an increase in population.

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