The relationship between body size and population abundance in animals

On average, large-bodied species live at lower densities than small-bodied ones. Early studies suggested that population densities might scale so that the energy use of a population is independent of body size. However, recent work shows that, at the scale of local communities, this is rarely true and that the pattern varies among taxonomic or ecological subsets of those communities. Energetic considerations may only be relevant to the densities of more abundant species. In fact, within natural assemblages o f organisms, the underlying relationship is very variable; in subsets of those assemblages, ecological processes such as competition may structure abundance patterns.