Species are embedded within multi-species communities, and interspecific competition is hypothesized to drive phenotypic evolution to reduce its intensity–character displacement, the process describing this phenomenon, is hypothesized to be widespread in nature, but evidence based on phenotypic traits may mislead inferences. We competed sympatric and allopatric populations of Vulpia microstachys and Bromus hordeaceus, two annual grasses, and concurrently measured phenotypic traits. Comparing the frequency dependence of both species' population growth rates among populations with sympatry vs. allopatric histories could reveal the strength and direction by which evolution impacts interspecific competition.
Results/Conclusions
In an invaded biodiversity hotspot, we show that rapid evolution is rescuing declining populations of native grass V. microstachys from exclusion by a European invader (B. hordeaceus). We additionally show that character displacement among this pair of competitors is maintained even in diverse natural communities, evolves repeatably among replicate populations, and contrary to classical hypotheses, is not achieved via increased niche differentiation. Our study provides a first demonstration that coexistence evolves in nature, highlighting evolution as an underappreciated coexistence mechanism that buffer species extinctions in the face of invasions.