Environment and space drive the community assembly of Atlantic European grasslands: Insights from multiple facets

Aim Ecological communities are assembled by regional and local processes. These processes select species through their traits, which are tied to species' evolutionary history. A multifaceted approach, encompassing taxonomic, functional and phylogenetic diversity can thus help us to better understand community assembly. We asked what the relative importance of geography, climate and soil parameters is in driving taxonomic, functional and phylogenetic diversities at local (alpha) and larger scales (beta diversity). Location Atlantic Europe. Taxon Plant communities of Violion caninae grasslands. Methods Alpha and beta taxonomic, functional and phylogenetic diversities were calculated for 153 sites. Traits were obtained from the LEDA database and phylogeny from Daphne. We summarized climatic (CHELSA database) and soil variables using principal component analysis (PCA), and geographical distance using Moran's Eigenvector Maps (MEMs). To assess the importance of environment and space on all three facets, we performed redundancy and distance-based redundancy analyses for alpha and beta diversity, respectively, using the PCA and MEM axes as predictors. Results Compared to alpha diversity, beta diversity was relatively high in taxonomic diversity, but very low in functional and phylogenetic diversity. Geography and climate were relatively more important at larger scales, whereas soil conditions acted more strongly at the local scales, with alpha diversity of all facets decreasing towards richer and acidic soils. Main Conclusions Considering multiple biodiversity facets along environmental and spatial gradients enables advancing both theoretical and applied aspects of community assembly. Accordingly, the observed turnover across the study area was mediated by species that share similar suites of traits and evolutionary history. Towards richer and acidic soils, exclusion of weaker competitors was an important filter at local scales. In summary, assessing multiple biodiversity facets and broad scale environmental gradients is key to understand the relative importance of multi-scale processes driving the community assembly of European grasslands.