Allometric slopes and independent contrasts: A comparative test of Kleiber's law in primate ranging patterns

At the most fundamental level, the size of an animal's home range is determ ined by its energy needs. In the absence of confounding variables, home ran ge size should therefore scale with body mass according to Kleiber's expone nt for metabolic rate of 0.75. Comparative studies in a wide range of taxa have failed to confirm this prediction: home range size has commonly been f ound to scale with an exponent significantly >0.75. We develop a comparativ e measure of metabolic needs that,incorporates both mass-specific metabolic rate and social-group size. We test the prediction that home range size in primates scales isometrically with this measure when an appropriate linear model is applied to data corrected for phylogenetic bias. Analyses using s pecies values as data points indicate an exponent consistent with Kleiber's law. This result is misleading, however, because ecological factors confou nd the analysis, and the slopes within some ecologically homogeneous taxa a re steeper. Accordingly, in analyses based on independent contrasts with re duced major axis, slopes are significantly greater than predicted by Kleibe r's law. We examine the effects of other variables, and we find that system atic variation in substrate use, home range overlap, and diet account for t he steeper than expected relationship between home range size and metabolic needs based on Kleiber's law. We therefore conclude that the scaling of ho me range size is subject to Kleiber's law but in combination with other fac tors. These results emphasize that the study of allometry requires detailed attention to statistical models and control of confounding variables.