Speciation of birds in Australia, New Guinea and the south-eastern Pacific islands

Abstract

The bird faunas of Australia, New Guinea and the south-western Pacific islands were graphically analysed in terms of distribution and ratios of species per genus. Models were then constructed that matched the real data closely. The form of these models gives rise to the following hypothesis about the course of evolution in the three areas. Three glacial and three interglacial periods have occurred; the glacial periods are seen as periods of movement of species, the interglacial as periods of speciation. Australia produces a maximum of four species per genus per interglacial, while New Guinea and the south-western Pacific Islands each produce five species per genus per interglacial.

Many more species have adapted themselves to life in rainforest in New Guinea and the south-western Pacific islands than in Australia. The difference appears to be because in Australia the amount of rainforest habitat is low, the rainforest habitat does not readily enable isolates to form, and many of the genera entering Australia do not have rainforest species and never invade the rainforest habitat.

This study also indicates that examination of isolated populations and subspecies in an area gives little quantitative information about evolution in that area. Suggestions that the south-western Pacific, because it contains archipelagos, is a rich area for production of species are not supported by the data presented here.