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 suppo...脊椎动物的捕食者与竞争者理论上可通过降低具备病原体储存能力的宿主（reservoir-competent hosts）的密度，或降低储存宿主身上的蜱虫负荷，从而降低感染蜱若虫密度（Density of Infected Nymphs，DIN）——这一蜱传疾病风险的常用量化指标。本研究针对荷兰境内20个捕食者丰度存在差异的森林样地，通过对比相关数据，探究了捕食者的这一潜在间接效应。在每个样地中，我们测定了宿主搜索型蓖麻硬蜱（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、啮齿动物种群密度、啮齿动物所携带的蜱虫负荷，以及哺乳动物捕食者的活动强度。我们分析了啮齿动物种群密度与啮齿动物身上的蜱虫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虫负荷如何预测三种病原体对应的宿主搜索型若虫密度与感染若虫密度。研究发现，两种啮齿动物身上的蜱幼虫负荷随两种捕食者的活动强度升高而降低；正如预期，三种病原体对应的宿主搜索型若虫密度与感染若虫密度均随啮齿动物身上的蜱幼虫负荷升高而上升。路径分析（Path analyses）支持……