Encounters with predators have a larger influence on the spatial distribution and movement of their prey than expected

Background/Question/Methods

Predators can have different non-lethal effects on prey, such as changes in their spatial distribution, movement patterns, vigilance, foraging behaviour, and group size. In many studies on these predator effects on behaviour of prey, a fixed predation risk is assumed. Under this assumption, density and behaviour of prey are compared between areas that differ in proxies for predation risk such as kill and carcass records, density of predator scats, and landscape features like woody cover and distance to water. Relatively little is however known about the effects of actual predator-prey encounters on the spatial distribution and movement of their prey. Using GPS collars on lion, wildebeest and zebra, we studied the effect of encounters with predator on prey behaviour in Welgevonden Game Reserve, South Africa. We tested whether (1) prey density is lower close to predators than further away, (2) prey runs away from predators after an encounter with a predator, and (3) prey avoids locations where a predator was encountered. We compared the observed prey response with the expected response based on null models.

Results/Conclusions

We found that zebra and wildebeest densities dropped strongly in the proximity of lion. Prey density was lower than expected up to around 750 m away from the predator. This is in contrast with the prediction based on the fixed risk assumption that prey density is low in areas of high predation risk. When zebra or wildebeest encountered lion, both prey species moved away from these locations at relatively high speeds. This behaviour was noticeable for 10 h after encounter. Finally, the distance of prey to the lion encounter location remained large during around 40 h after encounter. These results show a clear effect of predator presence on the spatial distribution of prey and their movement pattern, locally supressing prey densities for a considerable period of time. Besides effects on vigilance, we argue that this predator effect on spatial distribution has large consequences for local foraging pressure. Our study contributes to knowledge about the effects of large carnivores on mammalian herbivores, and hence the possible effects of these herbivores on the vegetation.