Interspecific competition and community structure in the introduced Hawaiian avifauna

The role of interspecific competition in structuring the introduced Hawaiian avifauna is evaluated using four separate analyses.

In the first analysis I calculated the extinction rate (extinctions per year) for columbiform and passeriform species for the period 1861 to 1960. I show that this rate is significantly nonlinear. This result is consistent with the hypothesis that interspecific competition has affected extinctions.

In the second analysis I show that the morphologies of surviving species on each of the six main Hawaiian Islands are not more different from each other than expected by chance alone. This suggests that competition either does not operate on morphology or that its effects are not extensive enough to produce non-random patterns in the morphologies of surviving species.

In the third analysis I show that congeneric pairs of of species are less likely to coexist if the species do not differ greatly in bill length. This result is consistent with the hypothesis of limiting similarity, and supports the argument that competition has played a role in affecting extinctions.

In the final section I test the hypothesis that species abundances are independent of their morphological similarity to other species in the community. This test revealed a weak, but significant, positive relationship between logarithm of abundance and mean Euclidean distance from each species to every other species.