The habitat requirements of four sympatric rock-dwelling macropods of the Australian monsoon tropics

A high diversity of rock-dwelling macropod species inhabit the tropics of the Northern Territory, Australia. Within this region, individual species have varied distributions, with ranges variously being widespread, restricted, or geographically disjunct with variable levels of sympatry between them. The cause of these patterns is unknown and little is known of the ecology of these rock-dwelling macropods. We hypothesized that differences in the habitat requirements is the key to understanding the biogeography and sympatry of the species. We examined this hypothesis at both regional and local scales. We analysed records of occurence of Petrogale brachyotis, P. concinna, Macropus bernardus and M. robustus and environmental correlates (such as geology type, vegetation type, distance to drainage and distance to 'rugged' terrain) throughout the monsoon tropics using geographic information systems and generalized linear modelling. We surveyed 80 sites across the tropics of the Northern Territory and collected presence-absence data using scats and environmental correlates to examine fine-scale habitat requirements. From the regional scale analysis, it was clear that distance to rugged terrain strongly influences presence of all four species. Responses to this variable suggest M. bernardus and P. concinna have greater requirements for rugged terrain, whereas M. robustus and P. brachyotis are found across a broader range of habitats. The local scale analysis suggested presence of M. robustus is primarily driven by vegetation type, M. bernardus by the cover of outcrops, boulders and large rocks, and P. brachyotis by the density of caves. Although these species overlap in their use of habitats, there are also differences in their habitat requirements that are likely to play a role in their niche separation and in some cases their biogeography. However, it is apparent that the distributions of the species have also been influenced by historical factors given the absence of these species from some apparently suitable sites.