Community-level interactions and functional ecology of major workers in the hyperdiverse ground-foraging Pheidole (Hymenoptera, Formicidae) of Amazonian Ecuador

Ants of the genus Pheidole are abundant and hyperdiverse, particularly in Neotropical rainforests. Very little is known, however, about the degree of ecological and behavioral differentiation of coexisting species comprising Pheidole communities. Additionally, the ecological role of the major worker subcaste, thought to be significant to the diversification of Pheidole, is poorly understood. We investigated the ecology and behavior of a ground-foraging Pheidole community of at least 56 species in Amazonian Ecuador. Pheidole species differed strongly in tolerance to flooding, nest site usage, foraging range, major worker foraging, and control of baits, but not in daily activity or ability to discover baits. A molecular phylogeny based on mitochondrial DNA was characterized by poorly resolved basal relationships and long terminal branches, suggesting an ancient diversification of many Pheidole lineages. Comparison of well-supported sister species suggests that both phylogenetic history and ecologically induced differentiation contribute to interspecific variation in Amazonian Pheidole. Ground-nesting species had larger major workers than twig-nesting species, whereas dominant species with stronger recruitment had a higher proportional abundance of major workers at baits. Variation among species suggests the presence of behavioral groups within the Amazonian Pheidole community that appear to segregate according to nest site usage and/or tolerance to flooding disturbance. Our results suggest an important role for major worker differentiation in the diversification of Pheidole.