Geographical patterning of species richness among granivorous birds in Australia

Aim To examine and compare patterns of species richness and prominence across the Australian continent for taxonomic and ecological subsets of the granivorous bird fauna. Location The Australian continental mainland and island of Tasmania. Methods Bird species records from the Atlas of Australian Birds (Blakers et al., 1984) were arranged in degree cells and analysed as raw tallies of species richness, and as averaged proportions of the recorded land bird assemblage. Results There were striking differences in the geographical distribution of absolute and relative abundance of foraging and taxonomic classes of granivorous birds. Granivorous birds that forage in trees are confined to the parrots and cockatoos (Psittaciformes), are most speciose in areas dominated by evergreen forests or woodlands and are equally species-poor in the arid-zone and the monsoonal tropics. In contrast, obligate terrestrial foragers are morphologically diverse and occur in all the families considered (Phasianidae, Turnicidae, Pedionomidae, Columbidae, Cacatuidae, Psittacidae, Passeridae). They are most speciose over a broad area of eastern, south-eastern and north-western Australia. Among obligate terrestrial foragers there is a marked latitudinal sequence of replacement of granivore taxa: finches (Passeridae) are most prominent in the monsoonal savannas, pigeons (Columbidae) are most prominent in the semiarid tropics, and parrots (Cacatuidae and Psittacidae) in the winter-rainfall arid and semiarid zones. Main conclusions These striking patterns may be related to differences in the size, bill shape and heat tolerance of the taxa, and to the history of evolution and/or colonization of the taxonomic group within Australia.