Body size, energy use, and community structure of small mammals

Body size has long been hypothesized to play a major role in community structure and dynamics. Two general hypotheses exist for how resources are distributed among body sizes: (1) resources are equally available and uniformly utilized across body sizes and (2) resources are differentially available to organisms of different body sizes, resulting in a nonuniform or modal distribution. It has also been predicted that the distribution of body sizes of species in a community should reflect the underlying availability of resources, with the emergence of aggregations of species around specific body sizes. I examined the relationship between energy utilization, body size, and community structure in nine small-mammal communities in North America. In all communities, energy use across body sizes was significantly different from uniform. In contrast, none of the nine species-level body size distributions were significantly different from uniform. Cross-site comparisons showed that, while the species-level body size distribution did not vary significantly among sites, the utilization of energy across body sizes did. These results suggest that uniform energy utilization does not occur in small-mammal communities and that the species-level body size distribution of a community is not determined by resource utilization.