Resource-Dependent Interactions and the Organization of Desert Ant Communities

Resources influence consumer physiology, behavior, population growth, interspecific interactions, and community structure. To understand fully the influence of resources on interactions among consumer populations and community structure, it may be necessary to understand the influence of resources on individual behavior. In the first part of this study, we examined how resource type influenced foraging behavior and interactions in a guild of omnivorous desert ants. Cafeteria experiments showed that Myrmecocystus depilis, M. mimicus, and Aphaenogaster cockerelli prefer protein resources to seed resources. However, A. cockerelli collects mostly seed resources, and M. depilis and M. mimicus collect mostly protein resources when faced with competition from one another. A temporary removal experiment showed that the effect of M. mimicus and M. depilis on A. cockerelli depended on resource type. At protein resources, Myrmecocystus foragers tended to displace A. cockerelli foragers, but at seed resources, there was no effect of one species on the other. In the second part of this study, we tested how resource availability may influence the arrangement of species in ecological dominance hierarchies. We found that there was considerable variation among sites in the arrangement of species, and that variation could be attributed to variation in resource availability and in the effect of particular species among sites. Our results suggest that the outcome of interactions between individuals are resource dependent, because individuals respond to resources in different ways. Furthermore, resource-dependent interactions and behavior can lead to communities that are arranged in intransitive dominance hierarchies, which may promote biodiversity at regional scales. Corresponding Editor: D. W. Pfennig.