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Competition and resource partitioning have been studied extensively as explanations for community structure and species coexistence in North American seed-harvester ants, but the biogeographical and historical context within which these communities have formed are poorly known. This paper examines biogeography of North American seed-harvester ants by constructing functional groups that serve to identify ecologically equivalent ant species that share a common evolutionary ancestry. Species were thus separated into functional groups based on genus and foraging method (solitary and group/trunk trail foraging species). Ecology, behavior, and micro- and macrodistribution patterns are then discussed and synthesized for species in each functional group. Overall, this discussion includes 42 ant species in the myrmicine genera Aphaenogaster, Messor, Pheidole, Ephebomyrmex, and Pogonomyrmex, about 5% of the total ant species in the United States.

The general pattern is that each functional group consists of a highly structured assemblage of ecologically equivalent ant species that are similar with respect to morphology, ecology, and behavior. The primary difference among species in each functional group is that each species occurs in specific micro- and macro-habitats, with the species replacing one another across contact zones that are delineated by abiotic habitat features. On a regional scale, species in these five ant genera are broadly sympatric, but only one species per functional group predominates at a locale. Re-examination of previously noted longitudinal dines of ant species richness and diversity suggest that rainfall is indeed correlated with these community attributes. However, patterns of species loss and species replacement across this rainfall gradient suggest that fewer ant species in drier locales is effected through limitations on mating flights and foundress survival rather than by seed abundance, as previously suggested.