Disturbance of ant community structure in Central Texas by the red imported fire ant, Solenopsis invicta

The introduction of a competitor into an established community provides an excellent opportunity to study the factors that maintain the dominance, diversity, and interactions of that community. The introduction of the red imported fire ant, Solenopsis invicta Buren, into North America provides such an opportunity. A transect, with pitfall traps as sampling units, was established in central Texas, U.S.A., from areas uninfested to heavily infested by S.. invicta. Cluster analysis of the species composition at particular localities depicts four distinct ant assemblages, two without and two with S.. invicta. A fifth aggregation of species was found and consisted almost entirely of S.. invicta. Principal components analysis reveals that disturbance of the habitat, mostly by humans, is the main factor controlling ant diversity. More specifically, increasing densities of the red imported fire ant were negatively correlated with species diversity. Conomyrma insane (McCook) can coexist with S.. invicta. probably because direct competitors or predators have been eliminated by S.. invicta. Ants of the granivorous guild, mostly Pheidole spp., that occur with the red imported fire ant are being displaced, whereas more generalistic ants, like Monomorium minimum (Buckley) and Forelius pruinosus (Roger), coexist with S.. invicta.