Study scale determines whether wildlife loss protects against or promotes tick-borne disease.

Abstract

How does wildlife loss affect tick-borne disease risk? To test this question, Titcomb et al. [1] excluded large mammals that typically support large numbers of adult ticks from 1 ha plots, and then quantified the density of questing adult ticks within exclosure versus control plots. A priori, one might expect reduced tick density within total exclosure plots, because adult ticks must take their final blood meal from an ungulate, hare or carnivore (hereafter ‘large mammal’; table 1), which were scarce to absent in exclosure plots ([1], fig. S1). However, contrary to expectations, Titcomb et al. report higher density of questing adult ticks of two species (Rhipicephalus pravus and R. praetextatus) in exclosure plots compared to control plots, whereas the density of a third tick species (R. pulchellus) declined in exclosure plots. Here, we examine three possible explanations for this counterintuitive result, expanding on the interpretation offered by Titcomb et al. We submit that high densities of questing adult ticks in exclosure plots indicate that the tick population there is failing, not flourishing. This pattern is maintained through time because small mammals import ticks from outside the plot. Therefore, this pattern would be expected to reverse in a larger plot.