The Introduced Hawaiian Avifauna: Biogeographic Evidence for Competition

We discuss the patterns of introduction and extinction of the species of land birds (passeriforms and columbiforms) introduced to the Hawaiian Islands over the last century. The data are consistent with the idea that rising extinction rates will eventually match immigration rates leading to a dynamic equilibrium. Turnover in species composition is a prominent feature of the introduced Hawaiian avifauna with extinctions common even among populations that had persisted for decades. We could not detect an effect of island size on extinction rate. However, the per species extinction rates do increase with the number of species on the island. This suggests that the species mutually affect each other's chances of extinction. Other explanations for an increasing per-species extinction rate do not seem to be consistent with our data. Thus, interspecific competition seems to have been an important process in determining extinction rate and, by extension, the equilibrium number of species on these islands.