Mutualisms as a driver of species’ spatial dynamics and their coexistence

Abstract

Understanding the determinants of species’ biogeography and the mechanisms driv-ing their coexistence are two fundamental ecological questions. Central to answering these questions is 1) delineating the interrelationships between species and their subsequent demographic effects and 2) unifying these relationships with dispersal, a ubiquitous property of species that determines their spatial distributions. My thesis centres the role of mutualisms (positive interspecific relationships) in influencing species spread and coexistence. First, I develop a mathematical model of two species mutualisms (e.g. plant-fungal interactions) to identify the conditions under which engaging in a mutualism promotes or hinders the spatial spread of species. Next, I extend the model to include competition between two dispersing species in the presence of a shared mutualist. Here, I enumerate the various coexistence outcomes between the competitors and the role of the mutualist in mediating coexistence. Finally, I incorporate ideas from metacommunity theory to describe a seed dispersal mutualism involving two competing plant species sharing a frugivore. I find that frugivore specificity and its predation and dispersal rates together shape plant species coexistence across connected habitats. Ultimately, my thesis addresses the gap in our knowledge on the role of mutualisms, a historically understudied interaction, in spatially structured ecological systems.