Small mammal assemblages in arid Australia: a reappraisal.

Abstract

Previous interpretations of small mammal assemblages in arid Australia are reappraised in the light of new knowledge. First, analysis of skeletal remains from the surfaces of cave deposits at 15 sites in the western ariel zone shows that species richness of rodents and polyprotoclont marsupials has declined to 44% and 41% of the pre-European numbers. Those species that survived European settlement tend to be small or to inhabit rocky outcrops. We suggest that the extinctions preferentially occurred among species that were more specialised in habitat or diet: the remaining species are relatively opportunistic (or r-selected). Consequently, current perceptions that "plagueing" species dominate small mammal assemblages were probably not true of the original fauna. Second, studies of seedeating animals in arid Australia suggest that birds and ants are the principal granivores because their body-plans best suit them to an uncertain seed supply resulting from climatic peculiarities; there is no evidence that they have excluded rodents from the seed resource over evolutionary time. Few Australian desert-dwelling rodents appear to be specialised granivores, probably because of the variability in seed supply. We suggest that the preponderance of work conducted on North American heteromyicl rodents has led to a misplaced assumption that granivory is the most successful way of life for desert-dwelling rodents, and that the prominence of omnivory and insectivory in Australia demonstrates that different arid ecosystems favour different trophic strategies among small mammals.