Testing resource-based models of patchiness in four Neotropical litter ant assemblages

In four Neotropical forests I studied how resource availability affected patchiness in litter ants, colonies of about 100 workers living in hollow twigs. At the regional scale, and contrary to Species Energy Theory, Costa Rica and Panama forests had similar species richness, despite the former being more productive. At the m(2) scale, nest densities varied 10-fold, often exceeding 10 nests/plot. I tested four predictions linking this patchiness to resource limitation and depletion. First, nest densities increased weakly with estimates of litter quantity and quality. Second, nest addition experiments doubled colony densities after four months in the two Panama assemblages. Third, colonies of most common species appeared to grow as fast when they were small as when they were large. Fourth, there was no suggestion of self-thinning among colonies: plots with large colonies did not have fewer colonies after removing the effects of litter. Combined, these results suggest that resources in the litter, most notably nest sites, may limit local patchiness, but that there is little evidence for food depletion. The unstable litter environment may preclude tropical litter ant colonies from growing large or populous enough to saturate their environment.