Fear of parasites: Lone star ticks increase giving-up densities in white-tailed deer

Nonconsumptive effects of predators on their prey are extensive and diverse, with significant consequences for community structure and ecosystem function. However, despite many theoretical similarities between predator-prey and host-parasite interactions, nonconsumptive effects of parasites on their hosts remain poorly understood. Further, such effects may be of consequence to human and wildlife health, when host-parasite interactions involve hematophagous arthropods that vector infectious diseases. We used giving-up density estimation techniques to measure the response of white-tailed deer (Odocoileus virginianus) to the risk of parasitism by lone star ticks (Amblyomma americanum), an important vector of several infectious diseases in the southeastern United States. We also deployed carnivore scent stations to estimate activity levels of potential deer predators, conducted deer dung count surveys to control for effects of deer abundance, and controlled for topographic aspect, a primary determinant of vegetative biomass and community composition. We found a significant, positive correlation between giving-up densities in deer and the densities of A. americanum, but no effect of canid predators, deer abundance, or topographic aspect. Our results are consistent with the few other empirical examples that demonstrate nonconsumptive effects of parasites on their hosts. Considering that host-parasite interactions have enormous potential to influence the prevalence of vector-borne diseases that affect human health, incorporating indirect effects of parasites on their hosts into infectious disease ecology may be necessary to effectively mitigate disease risk.