A continent-scale test of multiple hypotheses on the abundances of Neotropical birds

Explaining variation in the abundance of species remains a challenge in ecology. We sought to explain variation in abundance of Neotropical forest birds using a dataset of population densities of 596 species. We tested a priori hypotheses for the roles of species traits, environmental factors, and species interactions. Specifically, we focused on four factors: 1) body mass (trait); 2) habitat type (environmental factor), 3) net primary productivity (NPP; environmental factor); and 4) species richness of competitors (species interaction). Body size explained much variation in density, although only when analyzed at higher taxonomic levels. Habitat type was a strong predictor of density. The relationship between density and productivity was weak. Densities were related negatively to the species richness of heterospecifics, however – this trend was particularly strong within closely related groups. Our results show that the influence of energetic factors such as body size and productivity ...