Body size and risk of extinction in Australian mammals

The link between body size and risk of extinction has been the focus of muc h recent attention. For Australian terrestrial mammals this link is of part icular interest because it is widely believed that species in the intermedi ate size range of 35-5500 g (the "critical weight range") have been the mos t prone to recent extinction. But the relationship between body size and ex tinction risk in Australian mammals has never been subject to a robust stat istical analysis. Using a combination of randomization tests and phylogenet ic comparative analyses, we found that Australian mammal extinctions and de clines have been nonrandom with respect to body size, but we reject the hyp othesis of a critical weight range at intermediate sizes. Small species app ear to be the least prone to extinction, but extinctions have not been sign ificantly clustered around intermediate sizes. Our results suggest that hyp otheses linking intermediate body size with high risk of extinction in Aust ralian mammals are misguided and that the focus of future research should s hift to explaining why the smallest species are the most resistant to extin ction.