Decoupled environmental filtering between plant taxonomic and phylogenetic diversities in a tropical heterogeneous landscape

The relative roles of local and regional processes in determining community assembly in heterogeneous landscapes are poorly understood. Generally, local floras encompass much fewer species than their corresponding regional flora. Such reduction partly results from the local action of environmental filtering, so that only some species from the regional pool can successfully establish in a particular habitat, based on their ability to survive and thrive under certain conditions. We hypothesized that filtering power varies across vegetation types, as these represent different habitats, and that lineages are filtered more effectively than species in more restrictive habitats. We assessed reductions in lineage and species richness from the regional pool to habitat-specific pools using floristic information gathered over three decades in a tropical landscape encompassing seven vegetation types with differing environmental constraints. We constructed the phylogeny for the regional flora based on a mega-phylogeny for seed plants and pteridophytes, and calculated three α-phylogenetic metrics (ses.MPD, ses.MNTD, and ses.PD). Vegetation types differed in taxonomic (range: 94–666 species) and phylogenetic (range: 5,410–21,661 Ma) α-diversities. Most habitat-specific floras were phylogenetically under-dispersed. By artificially creating increasingly smaller reference species pools, we showed that the most speciose floras do not necessarily possess the highest phylogenetic diversity. Stronger filtering of lineages than of species in harsher habitats results in differential filtering power across heterogeneous landscapes and may underlie the decoupling of taxonomic and phylogenetic diversities.