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 twenty 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.从理论层面而言，脊椎动物的捕食者与竞争者可通过两种途径降低感染若蜱密度（density of infected nymphs, DIN）——这是衡量蜱传疾病风险的常用指标：一是降低具有病原储存能力的宿主的种群密度，二是降低寄生于此类宿主的蜱虫寄生负荷。本研究针对捕食者的这一潜在间接效应展开探究，对比了荷兰境内20个捕食者丰度存在差异的森林样地的调查数据。在每个样地中，我们测定了以下指标：活动期蓖麻硬蜱（Ixodes ricinus）若虫密度（DON）、三种病原体对应的感染若蜱密度（DIN）、啮齿动物种群密度、啮齿动物体表的蜱寄生负荷，以及哺乳动物捕食者的活动强度。我们分析了两个核心问题：一是啮齿动物密度与啮齿动物体表蜱寄生负荷是否与捕食者活动强度存在相关性；二是啮齿动物密度与蜱寄生负荷如何预测上述三种病原体对应的活动期若蜱密度（DON）与感染若蜱密度（DIN）。研究结果显示，两种啮齿动物体表的幼蜱寄生负荷随两种捕食者的活动强度升高而降低；同时，正如理论预期，三种病原体对应的活动期若蜱密度（DON）与感染若蜱密度（DIN）均随啮齿动物体表幼蜱寄生负荷的增加而升高。路径分析结果证实，两种捕食者的活动强度与活动期若蜱密度（DON）及感染若蜱密度（DIN）之间存在间接负相关关系。本研究结果表明，捕食者确实能够减少寄生于具有病原储存能力宿主的蜱虫数量，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。