Population abundance and body size in animal assemblages

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Abstract
Studies of the relationship between body mass and population abundance for terrestrial and aquatic animal species based on pooling data from many taxa and assemblages suggest that abundance scales with mass to the —0.75 power. Because metabolic rate scales with mass as (plus) 0.75, this result has been taken as evidence that all species in assemblages use equal amounts of energy. The evidence for ‘energetic equivalence’ is, however, equivocal, because within many individual assemblages the scaling of abundance on mass differs significantly from —0.75. Here, we present a summary of patterns of size and abundance in a number of different terrestrial, freshwater and marine animal assemblages, with the aim of discovering whether there is any generality in size-abundance patterns within assemblages, and whether any generality might hold across terrestrial, freshwater and marine environments.