The contrasting roles of human and natural predators in disease dynamics of prey populations

Background/Question/Methods

Predators play a key role in wildlife disease dynamics. For example, the ‘healthy herds’ hypothesis predicts that predators reduce parasite prevalence in prey through selective predation of infected individuals. However, predators can also amplify disease transmission by contributing to pathogen spread or persistence. Given different phenotypic targets, natural predators and humans (i.e., hunters) might have divergent effects on disease transmission. We hypothesized that humanity’s tendency to select healthy, adult prey would be less likely to decrease disease transmission in prey compared with natural predators, which often select younger or sicker prey. Moreover, we predicted that humans would be less likely to have non-consumptive effects on disease transmission compared with natural predators, which exhibit a greater diversity of predatory strategies and whose presence on the landscape is less ephemeral. We examined these hypotheses using studies identified in systematic quantitative literature review.

Results/Conclusions

Data from an initial 16 studies of predators from terrestrial ecosystems revealed 37 effects of predation on a disease outcome in prey; disease transmission decreased in 9 cases, increased in 10, did not change in and had no detectable effect in 18. The mechanisms by which predation influenced disease dynamics were similarly diverse, including 3 cases of consumptive effects (e.g., density reduction), 6 cases of trait-mediated effects (e.g., immunosuppression), 9 cases of predator-mediated effects (e.g., feeding behaviour), and 3 cases of selective predation. Ultimately, this research may lead to better understanding of the ecological role of predators in disease regulation. Further, by contrasting humans with natural predators, this work may identify ways by which managers can regulate the behaviour of hunters to minimize disease risks.