Niche theory for mutualism: A graphical approach to plant-pollinator network dynamics

Contemporary niche theory is a powerful framework for understanding how organisms interact with each other and with their shared environment. The graphical representation of the theory, as popularized by Tilman, facilitates the analysis of the equilibrium structure of complex dynamical models including species coexistence. This approach has so far been applied primarily to situations of resource competition, in accord with the general focus of work on ecological interactions since the 19709s. In this manuscript, we expand contemporary niche theory to integrate mutualistic interactions through a systematic analysis of mutualistic plant-pollinator networks. Specifically, we investigate the dynamics of a consumer-resource model of plant-pollinator interactions that has been extensively studied in numerical simulations and whose predictions have been tested against field data. We provide simple explanations in graphical terms for the qualitative phenomena consistently found by extensive numerical simulations, including the effects of nestedness and adaptive foraging on community dynamics, and the effects of invasions by new pollinator species. We also use this representation to highlight general similarities and differences between mutualistic systems and the more well-studied scenarios of pure competition.