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Both large-wildlife loss and climatic changes can independently influence
the prevalence and distribution of zoonotic disease. Given growing
evidence that wildlife loss often has stronger community-level effects in
low-productivity areas, we hypothesized that these perturbations would
have interactive effects on disease risk. We experimentally tested this
hypothesis by measuring tick abundance and the prevalence of tick-borne
pathogens (Coxiella burnetii and Rickettsia spp.) within long-term,
size-selective, large-herbivore exclosures replicated across a
precipitation gradient in East Africa. Total wildlife exclusion increased
total tick abundance by 130% (mesic sites) to 225% (dry, low-productivity
sites), demonstrating a significant interaction of defaunation and aridity
on tick abundance. When differing degrees of exclusion were tested for a
subset of months, total tick abundance increased from 170% (only
mega-herbivores excluded) to 360% (all large wildlife excluded). Wildlife
exclusion differentially affected the abundance of the three dominant tick
species, and this effect varied strongly over time, likely due to
differences among species in their host associations, seasonality, and
other ecological characteristics. Pathogen prevalence did not differ
across wildlife exclusion treatments, rainfall levels, or tick species,
suggesting that exposure risk will respond to defaunation and climate
change in proportion to total tick abundance. These findings demonstrate
interacting effects of defaunation and aridity that increase disease risk,
and they highlight the need to incorporate ecological context when
predicting effects of wildlife loss on zoonotic disease dynamics.
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