Population Density, Body Mass and Niche Overlap in Australian Birds

There is a negative relationship between body mass and ecological population density across 200 species of Australian birds, with a slope of -0.82 on logarithmic axes. This is not significantly different from the slope predicted by the energetic equivalence rule. 2. Contrary to previous studies, there is no tendency for the phylogenetic position of an individual tribe to correlate with the strength of the mass-density relationship across its species. 3. However, in line with recent theory, there is a relationship between the degree of niche overlap among species in a tribe and the abundance pattern of the species. Tribes in which the species appear to share few resources are those in which the relationship between mass and density is most strongly negative