Interspecific Competition, Island Biogeography and Null Hypotheses

We conducted a field study of some of Darwin's Finches (Geospiza species) in order to assess the relative importance of interspecific competition and habitat features in determining the observed biogeographic, ecological and morphological characteristics of these species (Abbott et aI., 1977). They employed stochastic models to generate expected beak size differences between sympatric species, and then compared expected with observed differences. Finding a generally close correspondence between expected and observed differences, they concluded that random processes are sufficient to account for the observations, and that therefore there is no need to invoke deterministic processes such as competition as we had done. Simberloff and his associates have also drawn the same conclusion from a series of other analyses performed in like manner