Resource Evolution Shapes The Contemporary Ecology Of Mutualisms In Communities

Background/Question/Methods

In many mutualisms, one or both species consume resources provided by their partner. For instance, many plants produce nutrients that feed mycorrhizal fungi, fleshy fruits that feed seed dispersing animals, and nectars that feed pollinating and defending animals. Crucially, the resource pool provided by one partner will vary through time as mutualists forage and as resource availability evolves via natural selection over many generations of interactions. How do ecological conditions shape natural selection on traits such as floral nectar volume that determine the supply of resources, and how in turn does resource trait evolution shape the contemporary ecology of mutualistic interactions? To explore these questions, we combine evolutionary trait dynamics and ecological population dynamics in a biologically-explicit model of a nectar-producing plant species interacting with a pollinator species and an herbivore species. In this talk, we address how this theoretical framework generates predictions regarding three key questions in mutualism ecology: 1) How does resource trait evolution shape the population dynamics of the interacting species? 2) How do ecological factors such as pathogens or abiotic nutrient availability affect the evolution of resource traits? And 3) how does the evolution of a mutualistic interaction affect one partner’s interaction with an antagonistic species?

Results/Conclusions

We present three main results emerging from our model that bear on how we study mutualism ecology in the wild. First, allowing nectar dynamics to evolve via selection from pollinators and other sources changes the population dynamics of the plant and pollinator species at the community equilibrium. Empirically, this suggests that studying selection on resource traits provides insight into the current and future ecological dynamics of consumer-resource mutualisms. Second, ecological factors that affect the population growth of either the plant or the pollinator species outside of the mutualism can shape the evolution of mutualistic interactions. This suggests that exploring external ecological factors that affect one or both partner species may be necessary for understanding patterns of mutualistic interactions across ecological gradients and in different types of communities. Third, feedbacks between the ecological and evolutionary dynamics of plant-pollinator interactions can shape the plant’s interaction with an antagonistic herbivore species. This result demonstrates how considering mutualisms between partner species may inform patterns in other types of species interactions. Overall, our model reveals that evolving resource traits help to shape the direct interactions among mutualists as well as their interactions with the broader community.