HISTORICAL RAIN-FOREST CONTRACTIONS, LOCALIZED EXTINCTIONS AND PATTERNS OF VERTEBRATE ENDEMISM IN THE RAIN-FORESTS OF AUSTRALIA WET TROPICS

The spatial patterns in the distributions of vertebrates in the rainfo rests of the wet tropics biogeographic region of north-eastern Austral ia were examined to form hypotheses on the processes that have shaped vertebrate assemblages and patterns of species richness and regional e ndemism. These rainforests occur in a relatively narrow and discontinu ous strip along the coast of north-eastern Australia. We found that th e number of regionally endemic species and the proportion of regional endemics present in each subregion are both strongly related to the ge ographic shape of subregional patches of rainforest, independent of ra inforest area, within Australian tropical rainforests. Shape has a mor e significant influence on regional endemism than area, and area has a stronger influence on species richness. These patterns were congruent for all terrestrial vertebrate classes (mammals, birds, reptiles and frogs), and for the four groups combined. Our results suggest that the combination of current rainforest area and shape are an index of the relative susceptibility of each area of rainforest to historical contr actions, with the implication that historical habitat fluctuations, co upled with subsequent localized extinctions (species sifting), have be en extremely important processes in determining current patterns of en demism in Australia's wet tropical rainforests. This hypothesis is sup ported by the highly nested structure of the subregional distribution patterns.