Determinants of species richness and similarity of species composition of land snail communities on Kimberley islands

Abstract

-We investigated patterns in species richness and similarity in species composition of land snail communities in relation to biogeographic and environmental gradients on continental islands along the Kimberley coastline of Western Australia. The camaenid land snails demonstrated high overall species richness, restricted geographical ranges (mostly to a single island) and almost complete turnover of species among islands. In comparison, the overall number of the smaller non-camaenid land snail species was much lower. They also had much wider distributions and a lower level of species turnover among islands. These results are consistent with the differing dispersal abilities of the two groups, one fostering in situ speciation and the other inter-island colonisation. We also show that dispersal ability was not the only driver of species richness and composition of land snail species on islands, but that rainfall, island area and availability of habitat also played a role. Rainfall was the major environmental driver of richness and composition for both groups of land snails. Rainfall was also highly correlated with extent of rainforest cover, habitat that provides a suitable micro-climate for snails and additional ecological niches compared to more open habitats.

Biogeographic patterns on Kimberley islands, Western Australia

“…The analysis by Gibson and Köhler (2012) showed that, at the generic level, both average annual rainfall and the extent of rock scree had the strongest association with compositional similarity. Two island clusters were also identified with the majority of islands in one cluster receiving an annual rainfall of greater than 1000 mm, and those islands receiving less than 1000 mm in the other (i.e.…”

“…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.…”

“…Indeed, no frogs were detected on seven out of the nine islands sampled that season (see Table 1). Additionally, I divided the land snails into two groups for the analyses -camaenids and noncamaenids -due to their vastly different dispersal capacities (see Gibson and Köhler 2012).…”

“…Two island clusters were also identified with the majority of islands in one cluster receiving an annual rainfall of greater than 1000 mm, and those islands receiving less than 1000 mm in the other (i.e. Hidden, Long, Sunday, Mary and Sir Graham Moore islands) (see Gibson and Köhler 2012).…”

“…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.…”