DISSERTATION RESEARCH The Mediating Effects of Food Web Structure and Habitat Complexity on the Occurrence of Terrestrial Trophic Cascades

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ABSTRACTFood-web structure, intraguild predation, and habitat complexity have often been implicated as important mediators of top-down effects, yet little experimental work has been done to specifically test the impact of these factors on the occurrence of trophic cascades (natural-enemy suppression of herbivores which results in enhanced primary production). Complex food webs, such as those with intraguild predation, may preclude trophic cascades because enemy impacts attenuate through a reticulate network of species interactions. However, habitat complexity may provide refuges for predators from intraguild predation, thereby simplifying the food web and enhancing the strength of top-down effects. By conducting manipulative mesocosm experiments, we propose to 1) determine the effects of food web complexity (predator species richness and predator functional group composition) on the occurrence of trophic cascades and 2) assess the role of habitat complexity in reducing reticulate interactions among predators and enhancing the strength of top-down effects. By determining how these factors influence the strength of top-down effects, generalizations can be made about the composition of systems in which cascades may occur. This predictive ability has broader impacts for both biological control (eliciting a trophic cascade in an agricultural setting) and species conservation (minimizing community-wide impacts following species loss or invasion).