PS 18-256 - CANCELLED - The effects of over-visitation in two-species pollination mutualisms

Abstract: Mutualisms are fundamental to ecological systems and provide services necessary to maintaining biodiversity. Due to their importance, researchers aim to understand the population dynamics of plants and animals that engage in these interactions, especially for pollination mutualisms. Recent theory on the population-dynamic response of two-species mutualisms to perturbations, which are increasingly common given anthropogenic impacts, captures several of the mechanistic, consumer-resource aspects of pollination. This theory remains flexible enough to consider any two animal and plant species. Importantly, it assumes that reproductive services provided to the plants by animals are a saturating function of animal visitation rates. In this study, we expand on prior work by incorporating the potential of over-visitation (e.g., animals destroying ovules at high visitation rates) to assess its impact on short-term plant reproductive output (i.e., benefit accrual) and long-term population dynamics. We incorporate a unimodal benefit accrual because empirical evidence reveals declines in benefit accrual at high visitation rates. Our approach consists of deriving from first principles the functional forms of benefit accrual that may lead to over-visitation, determining the resultant conditions for equilibria and threshold effects, and performing bifurcation and sensitivity analyses on transient and asymptotic system dynamics. Our studies reaffirm the inferences of prior models in demonstrating asymptotically stable coexistence at high population sizes and threshold effects of extinction at low population sizes for both partners. This study demonstrates the ecological conditions under which benefit accrual functions are likely unimodal and of dynamical consequence to the stability of plant-pollinator mutualisms.