Ant Community Structure: Effects of Predatory Ant Lions

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Abstract
This study examined the responses of ground—foraging ants to larval ant lions (Neuroptera: Myrmeleontidae). In central Oklahoma, these sit—and—wait arthropod predators are restricted by abiotic factors to sheltered cliff bases. A high—density ant lion zone forms an effective "minefield" of predation for local ant assemblages. The density of ant—nest entrances and the number of pitfall—trap captures of ant foragers were significantly lower in the ant lion zone than in the adjacent forest or grassland. Differences in ant abundance could not be attributed to differences in thermal microhabitat within and outside the ant lion zone. Over a 24—h period, ants foraged continuously at tuna—fish baits 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 common ant species in the assemblage. Among species, predation risk was negatively correlated with worker body mass. Manipulative field experiments tested whether ants use biotic or abiotic cues to avoid ant lion aggregations. Ants foraged readily at baits on the forest floor and baits placed in the center of experimental sand patches, but they avoided baits placed in sand patches that contained ant lions. Ant foraging was also substantially lower in patches from which ant lions had been removed 3 h prior to the start of the experiment. Ant foraging was slightly reduced in patches with artificial ant lion pits that had never contained predators. These experiments suggest that ants use biotic cues associated with the presence or recent presence of predators. Previous studies have not implicated predation as an important factor structuring ant communities. This study suggests that predators can have important community—wide impacts on the distribution, abundance, and behavior of ground—foraging ants.

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