The role of species pools in determining species diversity in spatially heterogeneous communities

1. The 'habitat-specific species pool hypothesis' proposes that differences between habitats in the sizes of their species pools are the main drivers of diversity responses to habitat heterogeneity. Empirical tests of this hypothesis are not trivial since species might be missing from ecologically suitable habitats due to limited dispersal, while others may occur in unsuitable habitats by means of source-sink dynamics and mass effect. 2. We tested the habitat-specific species pool hypothesis in a local, environmentally heterogeneous community of annual plants using a novel 'ecological selection' experiment. Mixtures of seeds representing the whole community were sown in each habitat, and the emerging species were exposed to six generations of selection by environmental filtering and competition while being blocked from dispersal. A comparison of the total number of species that were able to survive in each habitat (i.e., to pass the selection test) with data on species richness in the n...