PARENT SESSION
Tuesday, August 8, 8:00-11:30 am
COS 20 - Food webs I: trophic interactions
Mississippi, Mezzanine Level, Cook Convention Center
Presiders: D Gruner

Changes in ant predatory function across a gradient of coffee management complexity.

Philpott, Stacy^*,1, ¹ Smithsonian Migratory Bird Center, Washington, DC

ABSTRACT- Several studies from agricultural systems demonstrate that ants are important predators and highlight some of the complex effects ants have on lower trophic levels. Ant diversity and assemblages are strongly affected by habitat changes and food web theory predicts that strong top-down cascades are less likely to occur as food web and habitat complexity and community diversity increase. To examine relationships between habitat complexity and predatory function, I excluded ants from coffee plants in coffee agroecosystems varying in floristic and structural diversity and complexity to ask whether habitat intensification affects the intensity of ant predation and whether observed changes in ant assemblages relate to any observed changes. Specifically, I studied the effects of eliminating ants from coffee plants on arthropod assemblages, herbivory, fungal disease, and coffee yields and also sampled ant assemblages in each management type. Overall, removing ants did not change total arthropod densities. Ants did affect densities of some arthropod orders but did not affect densities of arthropods with particular feeding strategies, and these effects did not change with coffee management type. For small arthropods (< 3 mm), however, the effects of ants differed with management system. In the sites with intermediate vegetation complexity, ant removal affected either particular arthropod orders (one site) or herbivore densities (the other site), but in sites with higher and lower vegetation complexity, ants did not affect any arthropods. Removing ants did not influence herbivory, berry borer damage, or yields, but fungal disease outbreaks were higher on plants without ants across all sites. Ant communities differed significantly with decreases in vegetation complexity; diversity declined, but ant abundance did not change. Overall, some effects of removing ants differed with management system, and others did not. Thus, there is no clear pattern that top-down effects of ants intensify or dampen with decreased habitat complexity.

Key words: trophic interaction, community ecology, coffee agroecosystem