Islands and scales: a biogeographic survey of reptiles on Kimberley islands, Western Australia

Abstract

-The Northern Kimberley region in north-western Australia has high biodiversity and conservation values, including a rich herpetofauna with high levels of endemism. To date, the numerous islands off the coast have been little surveyed. We surveyed 24 of the largest islands along the Kimberley coast for reptiles between 2007 and 2010, to improve our understanding of biogeographical patterns of the region and to locate populations of species that may be threatened by factors including changed fi re regimes and Cane Toad invasion. We recorded 79 species of terrestrial reptiles. Species richness ranged from 14 to 32 taxa per island (mean = 22), and tended to increase with island area. Many taxa (36.7%) were Northern Kimberley endemics, 10 of which are only known from island populations. There were numerous new records for islands, range extensions and the discovery of at least three new taxa. Classifi cation based on species presence/absence data identifi ed several distinct clusters of islands, with geographical location of islands, extent of rugged, rocky habitat and climatic gradients at a regional scale having important infl uences on reptile communities. The main cluster of nine islands with the greatest species richness, including richness of Northern Kimberley endemics, was located in the high rainfall zone of the north-west Kimberley. Islands in this cluster were also generally larger in size and they were the most rugged. Island clusters in the mostly drier areas to the north and south had less diversity and often different taxa to the north-west Kimberley cluster. The remaining islands-Adolphus, Sir Graham Moore, Mary and Kingfi sher-were all distinct in the classifi cation analysis. The Kimberley islands harbour unique taxa and reptile assemblages, as well as numerous species known to be vulnerable to Cane Toad toxins and, as such, are important conservation refuges. Careful consideration is required of any proposals to develop the islands, and ongoing surveillance and quarantine is necessary to prevent the introduction of invasive species.

Biogeographic patterns on Kimberley islands, Western Australia

“…The sampling strategy used was specifi c to each of the targeted taxonomic groups and detailed elsewhere (see Doughty et al 2012;Gibson and Köhler 2012;Gibson and McKenzie 2012b;McKenzie and Bullen 2012;Pearson et al 2013;Palmer et al 2013;Lyons et al 2013). We aimed to sample each of the taxonomic groups as systematically as possible within each of the selected habitat types.…”

“…The relatively larger islands such as Augustus, Bigge and Boongaree tended to be the focus of previous surveys, however correlations between island area and survey effort were low to moderate (bats: 0.37; birds: 0.56; reptiles: 0.57; non-volant mammals: 0.62), suggesting a limited bias. The likelihood of false absences and their implications, as well as the adequacy of the sampling more generally, are further discussed in the relevant papers focusing on each taxonomic group (see Doughty et al 2012;Gibson and Köhler 2012;Gibson and McKenzie 2012b;McKenzie and Bullen 2012;Pearson et al 2013;Palmer et al 2013;Lyons et al 2013). While our knowledge on each of the taxonomic groups we sampled on individual islands is likely to be incomplete, the KIBS substantially improved this knowledge, and the analyses revealed strong Results of AIC c -based model selection for the species richness of Northern Kimberley endemic species on the islands sampled during the KIBS (four most supported models shown); also shows maximised loglikelihood function [log(L)], number of model parameters (K), AIC c differences (Δ i ), Akaike weights (w i ) and percent of deviance explained by each model (%Dev).…”

“…reptiles: Lerista greeri, L. griffi ni and Varanus glebopalma; birds: Australian Kestral, Little Eagle and Australian Owlet-nightjar; land snails: Gastrocopta macdonnelli and Eremopeas interioris; plants: Templetonia hookeri and Acacia hippuroides) (Johnstone and Storr 1998;Storr et al 1999;Wilson and Swan 2003;Köhler et al 2012) and includes examples where species of the high rainfall zone of the Northern Kimberley have been replaced by drier area species (e.g. the gecko Gehyra xenopus was replaced by G.occidentalis; see Palmer et al 2013). These islands also lack well-developed monsoon rainforest and consequently species restricted to that habitat type.…”

“…There were only 10 vertebrate species recorded on the islands that do not have known mainland distributions, all reptiles (Palmer et al 2013). However, it is likely that they have not been recorded on the adjacent mainland due to the lack of sampling along the Kimberley coastline, as all 10 species were on near-shore islands.…”

“…The taxonomic groups targeted include the nonvolant mammals, bats, reptiles, frogs, land snails and vascular plants, and birds were sampled opportunistically (see Gibson and McKenzie 2012a). Assessments of the biogeographic patterns in relation to island-wide attributes for each of these groups have been presented in a series of papers (see Doughty et al 2012;Gibson and Köhler 2012;Gibson and McKenzie 2012b;McKenzie and Bullen 2012;Pearson et al 2013;Palmer et al 2013;Lyons et al 2013). Overall, the survey revealed the presence of additional island populations of many vertebrates, and more than doubled the species lists for most of the islands where prior biological information existed.…”