Patterns of intraspecific and interspecific allometry in Old World primates.

A series of 22 variables representing many skeletal elements were measured on a sample of 255 individuals from ten species of Old World primates to discover for which variables intraspecific or intragroup allometric curves differed from interspecific curves. Skeletal weight was used to represent size. These results were then used to evaluate several hypotheses that have been advanced as possible explanations of such differences. Two explanations seem likely to apply frequently, but in different cases. First, the correlation between a variable and size is often low intraspecifically so that the reliability of the curve describing the relationship is poor. This applies equally to results from least-squares regression or reduced major axis. The low correlation may result from a situation in which a feature need not vary in close response to body size intraspecifically. The interspecific curve would be produced as a result of different optima in a series of species. Second, the results for many variables suggest that the nature of an organism's adaptive response to change in size differs between groups. The intragroup (or intraspecific) curves describe that response, while the interspecific curve is a summary of the consequences of size across all the included groups, which may be heavily influenced by the differing adaptations of those groups.