Non-metabolic explanations for the relationship between body size and animal abundance

Metabolic constraints are the usual explanation for the relationship between body size and species abundance in natural assemblages of animals. In some assemblages, abundance scales with body weight to the -0.75 power. Metabolic rate scales as weight raised to the (plus) power, therefore, on average equal amounts of energy are available to each species in a community. This equality has been taken as evidence that a species' abundance is limited by its energetic requirements. But most species in samples of complete assemblages cannot be energy limited (although the most abundant species, at the "upper bound' may be). And arguments also ignore the frequency distributions of species; body size and species; abundance which underlie abundance versus size plots. The authors test the hypothesis that concatenating the underlying frequency distributions of species' body size and species' abundance can directly account for observed patterns in plots of size versus abundance in assemblages of animals, comparing the negative slope of the upper boundary of plots of size against abundance from real assemblages, with the same slopes derived from models with no energy constraints. Models give estimates for the upper bound slopes that are very similar to slopes calculated from real assemblages. Patterns of abundance versus body size in natural assemblages thus may not be constrainted by species' energy requirements, and do not require explanations independent of those for the constituent frequency distributions of size and abundance. -from Authors

Duke Scholars

Author Stuart L. Pimm Environmental Natural Science