Predation risk can drive cycles in zoonotic disease prevalence

The recent increase in human cases of leishmaniasis in northern Israel has been accompanied by dramatic anthropogenic changes in the landscape that affect the behavioral ecology of one of its mammalian reservoirs, the rock hyrax, Procavia capensis. Hyraxes migrate from refuge to refuge, presumably following forage availability, but their migration patterns are strongly affected by the availability and spacing of the rock piles that form their den sites and give them protection from predators. We therefore expect changes in predation risk to influence the ability of hyrax groups to migrate from site to site. We combine mathematical metapopulation models of hyrax behavioral ecology, as well as compartmental models of disease dynamics, to investigate the effect of microhabitat alteration and varying perceived predation risk on disease incidence. Our models indicate that such fine-scale alterations in predation risk can have surprising effects on pathogen prevalence, leading to the emergence of epizootic cycles. Regular (predictable) cycles and chaotic (unpredictable) cycles may occur as predation risk is reduced. Under some conditions, cycles may result from very small changes in predation risk or environmental conditions. Our models show regions of sensitive dependence on environmental and predatory conditions, leading us to predict the possibility of the emergence of chaotic disease cycles as the result of small environmental disturbances.