Body size predicts degree in ant-plant mutualistic networks

The complexity of ecological communities can often hinder understanding their structural features. With the recent application of network theory, the structure of previously neglected mutualistic communities has begun to be elucidated. Mutualistic communities have now been shown to follow particular power distributions in their degree, that is, the number of species interactions per species. However, predictive variables of degree and other structures of mutualistic networks remain largely unexplored. Here, we show that body size of ants is positively correlated with their degree in mutualistic networks comprised of ant interactions with extrafloral nectar (EFN) bearing plants in the Sonoran Desert. This pattern in body size and the number of plant species with which ants interact occurred among all eight sampled communities, a relationship which was not contingent upon phylogenetic history among ant species. These results indicate that further study of body size in ant-plant and other mutualistic networks may yield promising insights into the processes influencing their structure. Moreover, the degree-body size relationship for ant-plant mutualistic communities is consistent with that of predator-prey food webs, possibly suggesting similar underlying processes at work.