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Causes and Ecological Context of Dietary Specialization in Neotropical Army Ants Open Access

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Understanding of the mechanisms that promote coexistence of species-rich predator assemblages in the Neotropics is critical for explaining the structure of diverse tropical communities. New world army ants are voracious predators of ants and other arthropods throughout the Neotropics, and up to twenty species may co-occur in one location. They therefore offer a valuable opportunity to address how predators may partition prey resources and coexist. While we know that each army ant species specializes on different ants and other arthropods, little is known about the mechanisms by which they locate and identify their preferred prey. In studying the closely related army ants in the genus Eciton, we asked the following interconnected questions: 1) Can army ants detect and distinguish between odors of prey and non-prey? 2) Do army ants prefer specific sources of prey-derived odors? 3) Do army ants use vibrational signals from potential prey irrespective of identity? 4) What is the dietary overlap among co-occurring Eciton species in Panamanian tropical forests? 5) Are Eciton burchellii army ants able to detect and attack preferred prey of their congeners? We filmed and measured army ant behavioral responses to several categories of prey-derived signals to determine the degree to which army ants use odors and vibrations to detect food and direct foraging. We found army ants are specialized on odors derived from preferred ant prey and ignore odors from non-prey ant species. Army ants also had varied responses to different sources of prey odors; prey nest material was most attractive, odors of live and dead prey were next most attractive, while alarm odors were not of any interest. Additionally, we found that army ant species responded differently to vibrations made by struggling arthropods, consistent with their divergent foraging strategies and diet breadths. To confirm this finding, we censused prey intake of the co-occurring Eciton in the Barro Colorado Natural Monument in Panama and found negligible dietary overlap at the prey genus and species level across the feeding guild. Finally, we found Eciton burchellii to be unable to detect odors of preferred prey of its congeners; however, vibrational stimuli allowed for a modest army ant response to potential prey irrespective of species identity. Taken together, these studies reveal that sensory specialization to prey-derived odor stimuli provides a mechanism by which army ants partition food resources, potentially promoting coexistence.

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