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 rela ted to environmental energy levels and to the efficiency of energy uti lization. We found that the intercepts, but not slopes, of density-bod y size relationships of the form log D = a + b log W differ significan tly 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 oth er literature estimates. Moreover, most of the interspecific variabili ty in density is related to differences in the mean densities of these groups (the dummy variables), not to body size per se. Mean populatio n density is also strongly, but negatively, related to potential evapo transpiration, a measure of crude atmospheric energy. Population energ y use decreases with body size in the pooled data, but it increases wi thin these metabolic groups because of the shallower relationship betw een density and body mass. Population energy use also increases slight ly with latitude, both because mean body size increases poleward, and independently of body size.