Determining variation in the success of New Zealand land birds



The New Zealand avifauna has changed considerably since the arrival of humans approximately 1000 years ago. The extinction of native species followed by their replacement with introduced exotic species is recognized as having greatly reduced the distinctiveness of the avifauna. Using phylogenetically independent methods, I tested whether life history and ecological correlates of extinction, introduction and persistence were significant across species and within taxa. Extinct land bird species were, on average, and independent of phylogenetic relatedness, larger-bodied than extant species. Introduction success was found to be significantly associated with increasing species body size, generation time and indices of human effort. In contrast, the geographical distribution of extant land birds was correlated with traits associated with high population growth rates (i.e. small, rapidly developing species, with high fecundity). My results suggest that selection pressures have changed significantly since the arrival of human colonists in New Zealand and that these changes have favoured different types of land birds, to the general detriment of endemic species. Comparative methods that explicitly examine historical changes are necessary to elucidate the changing roles of biological and extrinsic traits in the differential success of species in any assemblage.