Do predators keep prey healthy or make them sicker? A meta-analysis

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. To quantify the overall magnitude and direction of the effect of predation on parasitism in prey, we conducted a meta-analysis of 50 empirical studies. We also examined how key attributes of these studies, including parasite type, study design, and predator interaction type (consumptive vs. non-consumptive) contributed to variation in the predator-prey-parasite interaction. We found that the overall effect of predation on parasitism differed between parasites and parasitoids and that predator interaction type, and whether a predator was a non-host spreader of parasites were the most important traits predicting the parasite response. Our results suggest that the mechanistic basis of predator-prey interactions strongly influences the effects of predators on parasites and that these effects, while context dependent, are predictable.