Species Number, Population Density and Body Size Relationships in Natural Communities

Abstract

Population densities reported in the literature for a large range of species drawn from different communities typically decrease with increased body size, but samples from feeding guilds within natural communities of both birds and beetles indicate that the highest population densities tend to be recorded from species of intermediate size. The large population densities recorded for some intermediate-sized species, but not small or large-siozed species, may be a sampling effect. Within 4 guilds of Bornean beetles and 2 guilds of North American birds, even though highest population densities are found among species of intermediate size, average population density and the variance of population densities is broadly similar for species in different size classes. A simulation study showed the shape of the three-dimensional surface formed from the relationships among number of species, population density, and body size for the null distribution within each guild. In most but not all guilds, the shape of the species-density (or species-abundance) curve is broadly similar for each of the size classes. There may be no detectable relationship between body size and population density within many animal communities. -from Authors