Unexpected productivity and invasion resistance in plant communities assembled from allopatric populations

Species with shared geographic history may show coevolution that reduces niche overlap and improves resource capture. Thus, plant communities assembled from sympatric source populations (shared locations) are predicted to be more productive and invasion resistant than those from allopatric sources (different locations), even with identical species composition. Using four native plant species from 15 environmentally similar locations across a broad region, we compared ecosystem function among communities assembled from allopatric or sympatric sources. Consistent with predictions of niche differentiation in co-occurring native plants, we observed more negative native plant-plant interactions in allopatric-sourced communities, and more positive interactions in sympatric-sourced communities. However, this did not translate into the predicted community-level outcomes. Unexpectedly, allopatric-sourced communities outperformed sympatric ones in all responses, with 34-42% more inflorescences, 17% higher survival, 21% longer growing season, 29-72% greater size, and after invasion, 70% less invader biomass. Two impactful native species grew larger and reproduced more when grown with allopatric neighbours, leading to greater invasion suppression, though the mechanism for this response is unknown. These findings challenge assumptions about the universal advantages of maintaining shared origins for community function and have broad implications for understanding plant competition and community assembly, as well as restoration of invaded ecosystems.