Drivers of beta diversity along a precipitation gradient in tropical forests of the Cauca River Canyon in Colombia

Aims Tropical dry forests are among the most threatened ecosystems on Earth, and understanding the effects of climate on their species distributions is critical to mitigate global change impacts. Here, we assessed the impact of precipitation and dispersal limitation by natural and anthropogenic causes on phylogenetic and taxonomic beta diversity of woody-plant communities. Location Cauca River Canyon in the Northwest Andean mountains, Colombia. Methods We used inventory data from 160 0.02-ha plots and a phylogenetic tree to calculate phylogenetic and taxonomic beta diversity and their components (nestedness and replacement) across plots. We used redundancy analysis to assess the effects of precipitation, spatial distance, and connectivity (a proxy of fragmentation) on changes in beta diversity metrics and estimated each variable's relative contribution. Results We found that both phylogenetic and taxonomic replacement were highly related to precipitation differences. Spatial distance and connectivity explained only a small proportion of the variance in phylogenetic and taxonomic replacement. None of the predictor variables explained phylogenetic or taxonomic nestedness. Conclusions Patterns of phylogenetic and taxonomic replacement across woody-plant communities suggest that species and clades are highly specialized to particular precipitation regimes with a minor role for dispersal limitation. Both climate change and fragmentation could drastically influence the future community composition of tropical dry forests.