THE RELATION BETWEEN BODY-SIZE AND ABUNDANCE IN A BIRD COMMUNITY - THE EFFECTS OF PHYLOGENY AND COMPETITION

Within a bird community in North America, abundance patterns correlate with the evolutionary history of the species. Tribes of birds which have no close relatives (ancient lineages) tend to have positive relations between size and abundance, i.e. larger species are more abundant than smaller ones. This is not true of less ancient tribes. Interspecific competition has been suggested as the explanation for such patterns and, for the first time, it is possible to test this hypothesis. Ancient tribes are those in which interspecific competition is found to be strong, and the strength of competition correlates significantly with the abundance patterns of tribes.