Plant competition during invasion under evolving toxicity and resistance

Background/Question/Methods

Rapid evolution has the potential to significantly affect the trajectory of species invasions. Recent research has shown both invasive species evolving to new environments in their introduced ranges, and native species evolving to the habit changes induced by invasive species. Both processes occur in the invasion of Alliaria petiolata, a well-studied invasive species in the eastern United States known for its allelopathic ability. A. petiolata has evolved increased levels of toxicity at low conspecific density and decreased levels of toxicity at high conspecific density. Meanwhile, the native species Pilea pumila has been shown to be evolving resistance to A. petiolata’s allelopathic chemicals, at cost to its ability to compete with other species and its own conspecifics. Several theoretical studies inspired by this system have been published but they involve simplifications such as restricting evolution to one species. We expand on the modeling efforts to allow a toxic invasive species and a resistant native species to coevolve using a quantitative genetic approach. We compare models with and without evolution to better understand how coevolution in competing species can alter the trajectory of invasion.

Results/Conclusions

While many parameter values lead to similar outcomes with and without evolution, we find that when evolution does matter, it generally leads to better outcomes for the native species. There is a much smaller number of parameter sets where evolution helps the invasive species. We focus on a few key parameters: trait variance, sensitivity to competitor trait value, optimal trait value, and trait tolerance, that determine the outcome of competition and coevolution in this type of system. We find that cases are generally either more ecology driven, or more evolution driven, depending on whether evolution helps the native species or the invasive species. We also find strong dependence on initial conditions, with initial trait values often affecting whether traits are lost, or evolve high values in an "arms race" type scenario. Our study emphasizes the importance of considering evolution in biological invasions, and has the potential to predict the outcomes of plant competition in invasions when coevolution is occurring.