Trade-offs in biotic interactions facilitate coexistence between native and exotic plants in a historically invaded community

Background/Question/Methods: As plant invasions increase worldwide, it is becoming increasingly commonplace to find coexistence between native and exotic plants. In many cases, this coexistence has occurred over decades or centuries. The mechanisms that facilitate long-term coexistence between natives and exotics are of fundamental importance to ecology and invasion biology, but remain largely unresolved. Recent research, however, has shown that asymmetries or trade-offs among species can facilitate coexistence and may explain long-term coexistence between native and exotic species in historically invaded communities. One common form of differentiation exhibited by natives and exotics is an asymmetry in competitive ability and predator tolerance, as exotics are often competitively superior, but more significantly impacted by predators. Here, we examined whether these asymmetries exist between native and exotic plants coexisting in a community that has been invaded for over two centuries and whether removal of these asymmetries reduces coexistence.

Results/Conclusions: Our findings show that coexisting native and exotic plant species in this historically invaded community exhibit pronounced asymmetries. We found that exotic species are competitively superior to native species, but are more significantly impacted by predators. Additionally, we found that suppression of predators mediated the outcome of competitive interactions, increased exotic dominance, and reduced coexistence patterns across our field sites. Collectively, our findings suggest that asymmetries in biotic interactions between native and exotic plant species may facilitate coexistence in these historically invaded communities. However, they also suggest that trade-offs between native and exotic plant species may not be entirely reciprocal and that predation on exotic plant species may be the most important factor regulating coexistence.