Studies of biological invasions provide the opportunity to better understand how ecological and evolutionary processes interact to influence population and community dynamics. However, invasion biology currently lacks a conceptual framework that integrates both processes. Game theory and the concept of evolutionarily stable strategies (ESS) may permit formulating both the ecological and evolutionary contexts for invasive species. An ESS is a set of strategies (species for our purposes) that, by definition, cannot be invaded by a rare alternative strategy. Successful invasions of exotic species often occur as a rare event within a recipient community. From the perspective of game theory, if a recipient community can be successfully invaded, then the community is not at its ESS and the invader has attributes that can exploit the community’s susceptibilities. We use the concept of an ESS to model five pathways whereby a community can be vulnerable to invasion: 1) competition with a novel invader, 2) predation by a novel invader, 3) an empty niche, 4) species replacement, and 5) species addition.
Results/Conclusions
The model suggests that invasion of a novel competitor results in incumbent replacement, whereby, the native competitors may slow but not prevent species replacement over evolutionary time. The invasion of a novel predator often results in prey extinction, but can also result in an evolutionarily keystone predator driving the evolutionary divergence of prey species leading to diversification and species coexistence. An empty niche can always be invaded provided the invader possesses a strategy that suits the unoccupied peak of the adaptive landscape. Results show how species replacement occurs when the invader arrives with a strategy that places it ahead of the native species along the same slope of an adaptive peak. Finally, an invader that arrives on the opposite side of an adaptive peak from a natives species permits coexistence that is ecologically, but not evolutionarily stable. Over time, the species that reaches the adaptive peak first will replace the other. Using game theory and the ESS concept ecologists can hypothesize and/or test for the pathway of invasion of an exotic species, and predict both the ecological and evolutionary implications for the recipient community. Understanding the pathways of invasion can inform managers on best practices, and suggest the likelihood of successfully preventing or curbing an invasive species.
