Conservation status of ants in an iconic region of monsoonal Australia: levels of endemism and responses to fire in the eastern Kimberley

Abstract

The remote and sparsely populated Kimberley region is a major centre of endemism in the Australian monsoonal tropics that is threatened by uncontrolled fire following the disruption of Aboriginal burning practices. A recent study of the ant fauna of the Mitchell Falls area of the northern Kimberley revealed that 44 % of the species are known only from the Kimberley region. The fauna appeared to be highly resilient in relation to fire. Levels of endemism in the Mitchell Falls region are likely to be particularly high because it occurs in a high rainfall zone (>1,200 mm per year) that is isolated from similar zones elsewhere in northern Australia. In contrast, the lower rainfall eastern and southern Kimberley form part of continuous climatic bands that extend right across northern Australia, and so species from these areas might be expected to be more widely distributed. Here we describe the ant fauna of Mirima National Park in the eastern Kimberley, in the context of a broader biogeographic analysis of the Kimberley ant fauna and an understanding of its response to wildfire. We specifically test two hypotheses: first, that the ant species of Mirima tend to be more widely distributed across northern Australia than those of Mitchell Falls; and, second, that Mirima ant communities are highly resilient in relation to fire, as revealed by a weak relationship with time-since-fire. Analysis of distributional ranges revealed that 24 % of Mirima ant species are known only from the Kimberley, which, as hypothesized, is substantially lower than at Mitchell Falls (44 %). Also as we hypothesized, the Mirima ant fauna shows little relationship with time since fire, with no systematic variation in ant species richness between sites with 1–4 years since fire, and no relationship between time since fire and site similarity based on overall ant species composition. Although our study indicates that levels of endemism in the ant fauna of the eastern Kimberley are lower than those in the northern Kimberley, they are still extremely high. It seems that at least a quarter of all Kimberley ant species are endemic to the region. This confirms the Kimberley as a highly significant region for ant biodiversity. We have also shown that the regional ant fauna is highly resilient in relation to the key threatening process in the region.