Biogeographic patterns on Kimberley islands, Western Australia

Abstract

-Australia's islands play a signifi cant role in the conservation of its biota. The near-pristine islands along the Kimberley coast of north-western Australia are important natural refuges that have been relatively isolated from many of the threatening processes affecting the adjacent mainland. Between 2007 and 2010, 24 of the largest of these islands were surveyed for non-volant mammals, reptiles, birds, frogs, bats, land snails and vascular plants. To facilitate the setting of conservation priorities, I examined congruence in the biogeographic patterns among these taxonomic groups and related those to island-wide attributes. A high level of congruence in both spatial patterns of species richness and community similarity across most of the taxonomic groups was found. Congruence in species richness was best explained by a strong relationship with island area; while congruence in community similarity was infl uenced by the dispersal ability of taxa. Average annual rainfall and the extent of rock scree (or ruggedness) on an island were also strong correlates of both spatial patterns in community similarity and richness of regional endemics. I also show that this pattern was not explained by richness differences of species between islands alone, but largely due to species replacement among islands. These patterns refl ect the greater diversity of regional endemic species and/or habitat specialists that are restricted to the relatively high rainfall and extensively rocky islands; whereas the drier islands typically support widespread generalists that have distributions that extend into the semi-arid and arid zones. In terms of conservation signifi cance, the largest islands in the most mesic section of the coast are important for their high species diversity, including regional endemics. However, the lower rainfall islands support unique assemblages, and some are also important for their threatened mammal species. The high level of island endemism of the camaenid land snails indicates that all the islands sampled are important in terms of representing their diversity. The results of the survey also support the hypothesis that these islands are microcosms of the adjacent Northern Kimberley mainland with 74% of mammal, 59% of reptile, 70% of frog, 69% of bird and 49% of plant species of the Northern Kimberley bioregion now known on the islands sampled. Future management of the islands requires strategies that minimise the risk of incursions by exotic species and appropriate fi re regimes to preserve habitat quality.

Tropical specialist vs. climate generalist: Diversification and demographic history of sister species of Carlia skinks from northwestern Australia

“…As expected given its restricted and insular distribution, diversity and population size for Johnstonei B were much lower than for Johnstonei A. The islands in which Johnstonei B occurs are “land‐bridge islands,” most recently isolated by sea‐level rise approximately 8,000 to 12,000 years ago (Nix & Kalma, ), and share much of their species diversity with the mainland Kimberley (Gibson, ). The high genetic divergence, corresponding to an estimated late Miocene separation, between Johnstonei A and Johnstonei B contrasts with the low divergence among island and mainland populations in other skinks sampled across the same region (within Johnstonei A and Triacantha B, and also Ctenotus inornatus ; Harradine et al., ).…”

“…The islands in which Johnstonei B occurs are "land-bridge islands," most recently isolated by sea-level rise approximately 8,000 to 12,000 years ago (Nix & Kalma, 1972), and share much of their species diversity with F I G U R E 3 Spatial clustering analyses of the nDNA lineages Johnstonei A, Triacantha A and Triacantha B. On the left side are GENELAND heat maps of posterior probability of belonging to cluster one, and on the right side are SPACEMIX geogenetic maps with admixture inference, although no significant admixture was found the mainland Kimberley (Gibson, 2014). The high genetic divergence, corresponding to an estimated late Miocene separation, between Johnstonei A and Johnstonei B contrasts with the low divergence among island and mainland populations in other skinks sampled across the same region (within Johnstonei A and Triacantha B, and also Ctenotus inornatus; Harradine et al, 2015).…”

Importance of dispersal routes that minimize open‐ocean movement to the genetic structure of island populations

“…These results suggest that the Kimberley island system is conducive to moderate levels of dispersal. Recent studies of the Kimberley Islands by Palmer et al (2013) and Gibson (2014) suggest that reptile dispersal may be aided by the large tides and frequent high-rainfall events that occur in the region, coupled with abundant vegetation that could function as rafts. Islands that are more isolated by ocean are much less likely to encounter migrants and are more susceptible to the effects of genetic drift (Hutchison & Templeton 1999).…”

Palaeoecology and sea level changes: Decline of mammal species richness during late Quaternary island formation in the Montebello Islands, north-western Australia

“…The study of islands has had a significant and enduring impact on both conservation biology and our knowledge of palaeobiogeography in Australia. Studies have included elucidating the effects of fragmentation, isolation, and extinction of both ancient and extant faunas, determining the importance of appropriate sizes for natural reserves, and providing insights into genetic diversity, evolution, and conservation in extant faunas (Mills et al, 2004;Barnosky et al, 2005;Laurance, 2010;Moro and Lagdon, 2013;Gibson, 2014;McDowell et al, 2015). Much of the Australian north-west shelf was exposed during the Last Glacial Maximum (LGM), which lasted from 26 to 19 ka, after which rapid deglaciation began, causing sea levels to rise and the shelf to be flooded by c. 7 ka (Veth et al, 2007;Reeves et al, 2013).…”