Nonlinearity in the predation risk of prey mobility

Odorous waste products such as urine and faeces are unavoidable for most animals and are widely exploited by predators and their prey. Consequently, waste accumulations can be risky and prey that increase their mobility to disperse and dilute their waste should avoid a high predation risk until this benefit is balanced by the increasing risks of random predator encounter. This hypothesis is tested for voles (Microtus spp.) in Finland vulnerable to predation due to the scent- and UV-attractiveness of their urine. Mortality and mobility of radio-collared voles showed a U-shaped relationship, regardless of vole sex, species or population cycle phase. The low risks for prey making intermediate movements suggests that predation risk can exert strong selective pressures on prey such that they have little rest from the risk of being killed.