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Abstract
Organisms navigate a complex set of interspecific interactions, among the most important of these being victimization by predators and parasites. Ecological theory suggests that predators should keep prey populations healthy by reducing parasite burdens. However, empirical studies show that predators often have minimal effects on, or even increase, parasitism in prey. In this dissertation I used a combination of meta-analysis, macro-ecological scale analysis, experimental field manipulation, and predictive spatial modeling to (i) rigorously assess the generality of predictions of negative effects of predators on parasites in prey and (ii) evaluate the importance of heterogeneities in natural systems to the strength and direction of these effects. I found, across these studies, that the effects of predators on parasites in their prey were varied, and frequently positive rather than negative. I also found that this variation in the strength and direction of effects of predators on parasites in prey was driven by a variety of factors, including parasite traits, host/prey species identity, and predator interaction types. In particular, we find strong evidence of the importance of both non-consumptive interactions and the sharing of parasites between predators and prey contributing to the unexpected positive effects of predators on parasites in prey, while negative effects of predators on parasites tend to be associated with consumptive interactions between predators and prey. More broadly, while I identify some useful general patterns, my dissertation provides strong support for the importance of the specifics of a system to predicting the outcome of predator-prey-parasite interactions.