Eco-evolutionary feedback reshapes competitive dynamics in an orchard fly system

The feedback between competition and evolution is central to hypotheses about the origin and maintenance of species diversity. Yet, whether competition-induced evolution is sufficiently rapid, consistent, and strong to maintain diversity on ecological timescales remains unresolved. We conducted an outdoor mesocosm experiment with four pairs of orchard fly species in which we manipulated species' ability to evolve to one another during interspecific competition. We found significant competition-induced rapid evolution across phenotypes, which typically shifted in parallel across species. This evolution strongly affected the competitive population dynamics of all species pairs, typically boosting the rarer species' abundance, and in one pair, reversing the abundance hierarchy. These results suggest that feedback between competition and evolution may be common and maintain species diversity on ecological timescales.