Area of home range (H) can be related empirically to body weight (W) by the formulation H = aW^k. The computed values of exponent k have generated controversy concerning potential differences between trophic groups and whether they differ from 0.75 (the value expected if area of home range is a function of basal metabolic rate). When large mammals are considered, the empirical relationship assumes the form H = .002W^1^.^0^2 for herbivores, H = .059W^.^9^2 for omnivores, and H = .11W^1^.^3^6 for carnivores. By treating the animal's energetic requirements and the productivity of its habitat explicitly, empirical values of k > 0.75 are shown to result from declining rates of production of utilizable energy per unit area of habitat with increasing body weight. While trophic status and weight modify the utilizable proportion of energy in the habitat, broad correlations also exist between size of home range and surrogate variables for productivity (precipitation and latitude). Differences in weight alone account for a large portion of the differences between male and female or subadult and adult home ranges. Behavioral phenomena need not be invoked. Differences between herbivores and carnivores are in the direction suggested for birds and mammals. Criticisms regarding inter-class and inter-tropic comparisons appear resolved.
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