Trait dimensionality in experimental and natural ecological communities

Classical niche theory predicts that species with more similar traits experience stronger competition, and thus, trait dimensionality, here defined as the number of independent traits per species in a community, plays a critical role in coexistence. Despite this, current studies often assume that communities are structured by only a few key traits. Here, we leveraged a theoretical framework that integrates phylogenetic information with repeated instances of community assembly to estimate the number of ecologically relevant traits required to support observed species richness in experimental and natural plant communities. We found that the inferred trait dimensionality is surprisingly high, often exceeding species richness, suggesting that many traits contribute to coexistence. Furthermore, we explored drivers of grassland trait dimensionality, and it depends in complex ways on area, species pool size, and latitude. Our findings indicate that local coexistence may rely on a larger number of traits than previously assumed, challenging low-dimensional trait-based views of community structure.