Evolutionary game theory gives a role to functional traits in ecological coexistence

Abdel H. Halloway, Department of Plant Biology, University of Illinois at Urbana-Champaign, Urbana, IL and Gordon G. McNickle, Purdue Center for Plant Biology, Purdue University, West Lafayette, IN

Background/Question/Methods
Ecological communities are composed of individual organisms of many different species interacting within the same time and space. The persistence of these interactions – i.e., coexistence – remains a fundamental question in community ecology. Numerous mathematical theories have been developed to explain coexistence, but these theories remain implicit, measuring coexistence primarily on measured interactions between species. Since a species’ traits, and in particular its functional traits, governs its interactions, incorporating functional traits into coexistence theories could help develop better explanations for coexistence. One potential framework to bridge functional traits and ecological coexistence is evolutionary game theory. In evolutionary game theory, individual organisms use their adaptations as strategies to achieve ecological objectives and receive a fitness payoff. Changes in the strategies to ones which give higher fitness represent evolution, and fitness translated into per-capita growth rate represents population dynamics. This combined eco-evolutionary theory may help scientists better understand the principles behind ecological coexistence. To test our idea, we created several in silico competitive communities derived through game-theoretic principles and analyzed them using a variety of mathematical theories and tools on ecological coexistence.
Results/Conclusions
The diversification in these communities were governed by parameters of disruptive and stabilizing selection. As assumed, the greater disruptive selection relative to stabilizing, the greater the number of species coexisting in that community. Measures of pairwise coexistence show all species pairs are capable of ecologically coexisting aside from a few species in a few communities. This coexistence was more so driven by lower fitness differences than niche differences. We also saw declining average strength of species interactions as species were added to a community. Other ecological aspects such as rank-abundance curves more likely resembled real communities in the species rich in silico communities. Overall, incorporating functional traits through evolutionary game theory replicates many of the patterns of coexistence that are seen in nature, offering a framework for understanding real ecological communities.