The diversity, ecology, and function of arboreal ants in coffee agroecosystems in Soconusco, Chiapas, Mexico

Agricultural intensification results in biodiversity loss potentially affecting the functional role of biodiversity within agroecosystems. Diverse predators may more strongly affect lower trophic levels, particularly if predator strategies are complimentary. I examined patterns of diversity loss and the ecological role of one predator, ants, in the coffee agroecosystem to understand the predatory function of ants, and the importance of ant diversity to that function. In farms representing a gradient of coffee intensification in Chiapas, Mexico, I investigated patterns and one possible mechanism for biodiversity loss (nest-site limitation). To examine the predatory role of ants I (a) introduced baits to coffee plants with ants, (b) examined effects of two ant species on arthropod assemblages using canopy exclosures and (c) compared effects of high- and low-diversity ant assemblages on arthropods, coffee damage and yields with exclosures in coffee plants. I also investigated if ant spatial distributions and if effects of parasitic phorid flies (Pseudacteon sp.) on recruitment of Azteca instabilis (an abundant, competitively dominant species), ant competitive hierarchies, ant diversity, and ant prey may potentially affect the overall function of ants in coffee systems. Coffee-foraging ant diversity declined with intensification and nest-site limitation of twig-nesting ants may be one mechanism causing this loss. Ants quickly and more often located and removed baits than other predators. Ant species significantly differed in their effects on canopy arthropods. A diverse ant assemblage functioned to reduce predators, herbivores, and parasites, without affecting coffee plants, whereas a low-diversity assemblage resulted in lower coffee yields. Generally, ants were distributed in patches and although this varied by species and with spatial scale, distribution patterns did not change with intensification. Phorid flies restricted recruitment of A. instabilis, decreased A. instabilis ability to attack herbivores, changed ant competitive hierarchies, and increased ant diversity, thus potentially affect the overall role of ants as predators. In sum, losses in ant diversity, the spatial distributions of ants, and influences of ant parasites may significantly influence ant communities and also strongly affect how ants function as predators within coffee agroecosystems.