PARENT SESSION
Oral Session # 95: Predator - Prey Ecology III: Aquatic Systems.
Presiding: J Vonesh
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 201.

Prey density can influence the effects of multiple predator species on the prey's predation risk.

Vance-Chalcraft, Heather^{*,1, 2}, Soluk, Daniel^{1, 2}, ¹ University of Illinois at Urbana-Champaign, Urbana, IL² Illinois Natural History Survey, Champaign, IL

ABSTRACT- Changes in prey density can influence the consumption rate of a single predator but it is not clear how prey density influences our ability to predict the combined consumption rates of multiple predator species. These combined consumption rates influence the distribution and abundance of prey. To determine whether interactions among predator species affect the prey's risk of predation at varying prey densities, we conducted experiments in artificial stream tanks that crossed 6 treatments consisting of 0, 1, or 2 predator species with three treatments varying in prey density. Our predators were hellgrammites, greenside darters, and creek chubs and our prey were mayfly larvae. We found that each predator species, when alone, consumed an approximately equal proportion of prey at all prey densities. The consumption rates of the multiple predator combinations increasingly deviated from our model's predictions as prey density increased. Thus, making generalizations about the prey's risk of predation in the presence of multiple predator species may be difficult based on single prey density experiments. Empirically derived functional response curves of multiple predator treatments may be needed in order for prey density to be incorporated into models that predict the combined impact of multiple predators on prey populations.

Key words: prey density, multiple predator species, functional response, non-additivity