A simple theory for the mesopredator release effect: when does an apex predator protect their shared prey from a mesopredator?

Abstract

Predation plays a variety of important roles in structuring ecological communities. The mesopredator release effect occurs when the removal of an apex predator increases the density of a mesopredator, which in turn reduces the density of their shared prey. The mesopredator release effect can pose significant challenges for predator management and biodiversity conservation. Although several mathematical models have proposed specific circumstances that induce the mesopredator release effect, no theory has yet provided general conditions for this effect. Here, we propose a simple mathematical model to clarify the general conditions that induce the mesopredator release effect. The model predicts that the mesopredator release effect will occur when 1) the carrying capacity of the mesopredator exceeds a certain threshold, and 2) the top–down effect of the apex predator is larger on the mesopredator than on their shared prey. These conditions unify those from previous models and match the existing empirical examples. The simplicity of our theory may be useful for developing system-specific guidelines to control the mesopredator release effect in various ecosystems.