• population density;
  • allometry;
  • energy flow;
  • body mass;
  • energy budget;
  • mammals -;
  • terrestrial animals;
  • aquatic animals;
  • metabolism

Global regressions of ecological population densities on body mass for mammals and for terrestrial animals as a whole show that local population energy-use is approximately independent of adult body mass—over a body mass range spanning more than 11 orders of magnitude. This independence is represented by the slope of the regressions approximating –0.75, the reciprocal of the way that individual metabolic requirements scale with body mass. The pattern still holds for mammalian primary consumers when the data are broken down by geographic area, by broad habitat-type and by individual community. Slopes for mammalian secondary consumers are also not statistically distinguishable from –0.75. For any given body mass temperate herbivores maintain on average population densities of 1.5 to 2.0 times those of tropical ones, though slopes do not differ. Terrestrial animals of all sizes exhibit approximately the same range of population energy-use values. These results agree with those reported for population energy-budgets. It is suggested that rough independence of body mass and the energy-use of local populations is a widespread rule of animal ecology and community structure.