Pollinator-Induced Density Dependence in Deceptive Species

Many animal-pollinated species experience low visitation rates and, in some cases, stand on the brink of extinction because they are poorly fertilized. Among these plants, some are deceptive species (flowering plants that do not offer any reward to their pollinators). A learning process that pollinators undergo determines visitation rate in those food frauds that do not mimic rewarding models. Pollinators that visit cheating species avoid them after having experienced the absence of reward a few times and then visit rewarding plants. We modeled this learning process, using classical optimal foraging and game theory tools, and applied our model to survey how visitation rate can be adjusted in deceptive species in a density-dependent way and how it can influence the population dynamics of those species. We found pollinator behavior to induce positive density dependence at low density (Allee effect) and therefore to create a threshold density under which population survival is not possible. Moreover, negative density dependence occurs at high density so that in most cases pollination limitation creates a stable demographic equilibrium. Stochastic simulations were performed to investigate the stability of populations at these equilibria and estimate their mean time to extinction. Because some parameters such as pollinator density or habitat fragmentation were explicitly taken into account, we tried to describe environmental conditions conducive to a deceptive plant's survival.