Variable effects of wildlife and livestock on questing tick abundance across a topographical–climatic gradient

Abstract

Large-bodied wild ungulates are declining worldwide, while domestic livestock continue to increase in abundance. Such changes in large herbivore communities should have strong effects on the control of ticks and tick-borne disease as they can indirectly modify habitat and directly serve as final hosts for ticks' lifecycles. Numerous studies have now linked changing ungulate communities to changes in tick populations and disease risk. However, the effects of changing large herbivore communities are variable across studies, and the effect of climate as a mediating factor of this variation remains poorly understood. Also, studies to date have largely focused on wildlife loss without considering the extent to which livestock additions may alter tick populations, even though livestock replacement of wildlife is the global norm. In this study, we used a large-scale exclosure experiment replicated along a topo-climatic gradient to examine the effects on tick populations of both large herbivore removal and livestock additions. We found that while questing ticks increased modestly, by 21%, when large herbivores were removed from a system they decreased more substantially, by 50%, when livestock (in the form of cattle) were added. Importantly, in addition to the direct effects of climate on tick populations, climate also mediates the effect of ungulates on questing tick density. Particularly, the addition of livestock under the most arid conditions decreased tick presence, likely due to changes in ground-level microclimates away from those beneficial to ticks. Overall, the work contributes to our understanding of tick population responses to globally common human-induced rangeland alterations under the concurrent effects of climate change.