ANT COMMUNITY STRUCTURE - EFFECTS OF PREDATORY ANT LIONS

This study examined the responses of ground-foraging ants to larval an t lions (Neuroptera: Myrmeleontidae). In central Oklahoma, these sit-a nd-wait arthropod predators are restricted by abiotic factors to shelt ered cliff bases. A high-density ant lion zone forms an effective ''mi nefield'' of predation for local ant assemblages. The density of ant-n est entrances and the number of pitfall-trap captures of ant foragers were significantly lower in the ant lion zone than in the adjacent for est or grassland. Differences in ant abundance could not be attributed to differences in thermal microhabitat within and outside the ant lio n zone. Over a 24-h period, ants foraged continuously at tuna-fish bai ts placed on the forest floor, but never utilized baits placed within the ant lion zone. Field behavioral tests with individual ant foragers confirmed that the risk of predation from ant lions was high for comm on ant species in the assemblage. Among species, predation risk was ne gatively correlated with worker body mass. Manipulative field experime nts tested whether ants use biotic or abiotic cues to avoid ant lion a ggregations. Ants foraged readily at baits on the forest floor and bai ts placed in the center of experimental sand patches, but they avoided baits placed in sand patches that contained ant lions. Ant foraging w as also substantially lower in parches from which ant lions had been r emoved 3 h prior to the start of the experiment. Ant foraging was slig htly reduced in patches with artificial ant lion pits that had never c ontained predators. These experiments suggest that ants use biotic cue s associated with the presence or recent presence of predators. Previo us studies have not implicated predation as an important factor struct uring ant communities. This study suggests that predators can have imp ortant communitywide impacts on the distribution, abundance, and behav ior of ground-foraging ants.