Phylogenetic structure of local communities predicts the size of the regional species pool

International audience1. The regional species pool is a set of species available in a region and ecologically suitable for growing in the particular environment occupied by a local community. As species pools are largely influenced by evolutionary processes such as the conservation of ecological niches within lineages we hypothesize that the size of the regional species pool increases with the variety of distinct phylogenetic lineages represented in a local community. We contrast this with hypotheses invoking diversification of individual lineages within environments or stochastic present-day assembly of local communities. 2. We calculated phylogenetic distinctness for a local community as the number of nodes separating two species averaged over all pairwise comparisons across a phylogenetic topology of a regional flora. We calculated the size of the regional species pool for a local community as the number of species in the regional flora that share the ecological niche position of the species constituting the local community. 3. Analysing field-layer communities across a wide range of environments, we indeed found that local communities composed of phylogenetically highly distinct species recruit from larger species pools than communities of low phylogenetic distinctness. Accounting for the presence of two particularly diversifying lineages (Poaceae and Cyperaceae) confirmed these results. 4. These results help us to understand how the species pool was assembled throughout evolution in different types of environments (immigration vs. in situ radiation of individual lineages). 5. The phylogenetic approach is of large practical value to infer the size of the regional species pool because phylogenies have become available for many groups of species worldwide, while knowledge of the species' ecological requirements or habitat affiliation (needed for the classical definition of species pools) is often still lacking. 6. Synthesis. We show that the size of the regional species pool can be predicted by the average phylogenetic distinctness between the species present in a local community. This approach contributes to the understanding of the causes of species richness in regional species pools and local communities. The approach is also an important tool for determining the size of the regional species pool when parameters other than species phylogeny are not known