Multiple determinants of Australian tropical frog biodiversity
Distribution data on rainforest frogs within 22 subregions of the Australian Wet Tropics were used to analyse biogeographic patterns in assemblage composition and diversity, and to relate these patterns to environmental factors. The ecological correlates of species richness and spatial patterns of assemblage structure suggested that the patterns of species richness fell into three categories, each being influenced by different processes. The species richness of habitat generalists was largely unaffected by rainforest variables and was primarily related to broad habitat diversity and climate. The spatial patterns of species richness of non-microhylid rainforest frogs were the result of processes associated with historical biogeography, especially extinctions and subsequent recolonisations in those subregions most affected by Quaternary fluctuations in rainforest area. This group of frogs has undergone severe population declines in recent years and the declines represent a significant loss in regional biodiversity since it is this group that produces the majority of regional variability in frog diversity. In contrast, the most significant influence on spatial patterns of microhylid species richness may have been in situ speciation in areas of consistent rainfall, driven by altitudinal gradients, isolation and low dispersal ability. These results stress the necessity of using meaningful and objective groups based on functional ecology in order to understand the determinants of biodiversity: it is not sufficient to examine patterns based purely on species richness within a broad taxonomic group.
HISTORY AND ARCHAEOLOGY