Biodiversity is imperilled by the spatial homogenization of life on Earth. As new species invade ecological communities, there is urgent need to understand when native species might resist or succumb to interactions with new species. In the California Floristic Province, a global biodiversity hotspot, we show that populations of a native grass (Vulpia microstachys) have evolved to resist the competitive impacts of a dominant European invader (Bromus hordeaceus). Contrary to classic theory, which predicts that competing species co-evolve to differentiate their niches, our evidence is instead most consistent with the native species having evolved to better compete for those resources used by the invader, curtailing the invader’s spread. Evolution to resist an invader was achieved despite populations interacting within a diverse background community (22 species 0.5 m^–2 on average), refuting the oft-cited hypothesis that high diversity precludes the evolution of pairwise species interactions. Lastly, unlike studies that have explored the demographic consequences of evolution under competition, ours does so with naturally evolved populations. Our study highlights evolution as an underappreciated coexistence mechanism, acting to buffer species from extinction in the face of biological invasion.

生物多样性受到地球上生命空间同质化的威胁。随着新物种入侵生态群落，迫切需要了解本地物种何时可能抵抗或屈服于与新物种的相互作用。在全球生物多样性热点加州植物区系省，我们发现原生草类 ( Vulpia microstachys ) 的种群已经进化以抵抗欧洲占主导地位的入侵者 ( Bromus hordeaceus ) 的竞争影响）。与预测竞争物种共同进化以区分其生态位的经典理论相反，我们的证据相反，与本地物种的进化最为一致，以更好地竞争入侵者使用的资源，从而减少入侵者的传播。尽管种群在不同的背景群落（22 种 0.5 m ^–2平均而言），驳斥了经常被引用的假设，即高多样性排除了成对物种相互作用的进化。最后，与探索竞争下进化的人口学后果的研究不同，我们的研究是对自然进化的种群进行的。我们的研究强调进化是一种被低估的共存机制，在生物入侵时起到缓冲物种灭绝的作用。