Data from: Cascading effects of predator activity on tick-borne disease risk

Predators and competitors of vertebrates can in theory reduce the density of infected nymphs (DIN)—an often-used measure of tick-borne disease risk—by lowering the density of reservoir-competent hosts and/or the tick burden on reservoir-competent hosts. We investigated this possible indirect effect of predators by comparing data from 20 forest plots across the Netherlands that varied in predator abundance. In each plot, we measured the density of questing Ixodes ricinus nymphs (DON), DIN for three pathogens, rodent density, the tick burden on rodents and the activity of mammalian predators. We analysed whether rodent density and tick burden on rodents were correlated with predator activity, and how rodent density and tick burden predicted DON and DIN for the three pathogens. We found that larval burden on two rodent species decreased with activity of two predator species, while DON and DIN for all three pathogens increased with larval burden on rodents, as predicted. Path analyses supported an indirect negative correlation of activity of both predator species with DON and DIN. Our results suggest that predators can indeed lower the number of ticks feeding on reservoir-competent hosts, which implies that changes in predator abundance may have cascading effects on tick-borne disease risk.脊椎动物的捕食者与竞争者理论上可通过降低储权宿主（reservoir-competent hosts）的种群密度，或降低储权宿主身上的蜱寄生负荷，来降低感染若虫密度（Density of Infected Nymphs, DIN）——该指标是蜱传疾病风险的常用评估方式之一。我们针对捕食者的这一潜在间接效应展开研究，对比了荷兰境内20个捕食者丰度存在差异的森林样地的监测数据。在每个样地中，我们分别测定了寻食型蓖麻硬蜱（Ixodes ricinus）若虫密度（Density of Questing Ixodes ricinus Nymphs, DON）、三种病原体对应的感染若虫密度（DIN）、啮齿动物种群密度、啮齿动物身上的蜱寄生负荷，以及哺乳类捕食者的活动强度。我们分析了啮齿动物种群密度与蜱寄生负荷是否与捕食者活动强度存在相关性，同时探究了啮齿动物种群密度与蜱寄生负荷如何预测三种病原体对应的DON与DIN。研究结果显示，两种啮齿类宿主身上的蜱幼虫负荷随两种捕食者的活动强度升高而降低；同时，三种病原体对应的DON与DIN均随啮齿类宿主的蜱幼虫负荷升高而上升，与理论预测一致。路径分析（path analysis）结果证实，两种捕食者的活动强度与DON、DIN之间存在间接负相关关系。本研究结果表明，捕食者确实可减少寄居于储权宿主身上的蜱的数量，这意味着捕食者丰度的变化可能会对蜱传疾病风险产生级联效应（cascading effects）。