How symbionts turning from friends to foes induce Allee effects in predators
Species continuously interact in a wide range of ways, which include mutualism and antagonism. Actually, such interactions can be reversed as a result of stress and environmental conditions. Here, we consider a predator-prey model, in which the prey's symbionts turn from mutualistic to antagonistic when the predator pressure increases. Such effects are represented by an attack rate, which continuously decreases or increases with the predator density, and directly affects the predator's functional response. We demonstrate that any functional response coupled with such an attack rate leads to Allee effects in predators as far as the functional response is increasing at low predator densities. Bifurcation diagrams for different functional responses indicate that increasing antagonism destabilizes prey-predator dynamics, but promotes bistability and potential extinction of predators. Our work thus shows that Allee effects in predators can emerge from dynamical interactions between species and may be more prevalent than expected. These results are especially interesting for biological control as they provide an innovative way for pest eradication by exploiting Allee effects in predators induced by antagonism on prey.