MAMMALS SF AUSTRALIAN ISLANDS - FACTORS INFLUENCING SPECIES RICHNESS

Distribution patterns of indigenous non-volant terrestrial mammals on 257 Australian islands were examined in relation to environmental para meters and the effects of human-induced disturbance during prehistoric and historic times on island species numbers. Species occurrence for individual species, for taxonomic and trophic groups, and for all spec ies together was related to environmental parameters using regression analysis and the extreme-value function model. Patterns of occurrence were examined separately within three major biogeographic regions deri ved by pattern analysis. The number of species known to have occurred on these islands during historic times was adequately predicted from a rea alone. No statistically significant improvement in predicted speci es number was gained by including island elevation, mean annual rainfa ll, isolation from the mainland or the number of potentially competing species present on the island. Similarly, no single factor other than area was found to influence consistently the presence of individual s pecies. We conclude that the occurrence of indigenous non-volant terre strial mammal species on these islands indicates a relictual rather th an equilibrial fauna. Visitation by Aboriginal people during prehistor ic times did not significantly increase mammal extinctions on islands. Examination of patterns of species richness for a given area on a reg ional basis showed that islands in and around Bass Strait and Tasmania (Bass Region) were the most species-rich, islands off the northern co asts were slightly less rich, and islands off the south western coasts had fewest species. This is in contrast to the usual latitudinal grad ient in species richness patterns. However, islands off the northern a nd eastern coasts had an overall greater number of different species. When considered in relation to the number of different species of mamm als occurring within each region, islands of a given size in Bass Regi on typically bore a higher proportion of this species pool than other regions. The Bass Region was found to be particularly rich in macropoi d herbivores and dasyurid carnivores and insectivores. Analyses indica ted that there is a very strong relationship between the presence of e xotics as a whole and the local extinction of native mammals. Many mam mal species formerly widespread on the Australian mainland are now res tricted totally to islands (nine species) or are threatened with extin ction on the mainland and have island populations of conservation sign ificance (ten species). In all, thirty-five islands protect eighteen t axa of Australian threatened mammals. The landuse and management of th ese islands is of considerable importance to nature conservation. The introduction of exotic mammals to these islands should be prevented; a ny introductions that occur should be eradicated immediately.