GLOBAL PATTERNS OF ANIMAL ABUNDANCE AND SPECIES ENERGY USE

There is enormous variation among animal species in Population density and population energy use. Density (D) is known to vary strongly with body weight (W). while allometric scaling of population energy use is disputed. The present study the hypothesis that the patterns are related to environmental energy levels and to the efficiency of energy utilization. We found that the intercepts, but not slopes, of density-body size relationships of the form log D = a + b log W differ significantly among broad groups: invertebrates, vertebrate ectotherms, mammals and birds. An overall regression that distinguishes among these groups using dummy variables has a much shallower slope (-0.56 than most other literature estimates. Moreover, most of the interspecific variability in density is related to differences in the mean densities of these groups (the dummy variables), not to body size per se. Mean population density is also strongly, but negatively, related to potential evapotranspiration, a measure of crude atmospheric energy. Population energy use decreases with body size in the pooled data, but it increases within these metabolic groups because of the shallower relationship between density and body mass. Population energy use also increases slightly with latitude, both because mean body size increases poleward, and independently of body size.