Roles of Alternative Prey for Mesopredators on Trophic Cascades in Intraguild Predation Systems: A Theoretical Perspective

Declines of apex predators can cause dramatic increases of smaller predators and ensuing collapses of their prey. However, recent empirical evidence finds that the disappearance of apex predators does not reduce but can increase prey populations. This poses a great challenge in managing species interactions involving mesopredator release. Here we analyze a mathematical model to explain variable consequences of apex predator loss and to develop management guidelines for prey conservation. The model formulates an intraguild predation system (apex predators, mesopredators, and their shared prey) with mesopredators supplied with additional alternative prey. We show that apex predator loss causes only negative effects on shared prey without alternative prey but has either negative or positive effects with alternative prey. Moreover, when alternative prey is highly abundant, apex predator loss causes strong mesopredator release and reduces shared prey greatly. Finally, the model suggests that a viable management strategy to restore shared prey under much uncertainty about a target system is to allocate a limited control effort not only to both predators but also to alternative prey. Alternative prey for mesopredators may be a crucial ingredient that controls the cascading dynamics of intraguild predation systems and should be considered as an important management target.