Global Diversification Rates of Ferns Across Spatial and Climatic Gradients

Geographic patterns of diversity in any group of plants are the result of the interplay of environmental conditions and the evolutionary dynamics of the respective plant group. Here, the geographic distribution of current mean diversification rates (MDR) is explored at the genus level for ferns and relate it to climatic conditions and regional species richness. It is found that MDR is highest at tropical latitudes and in humid and hot environments, and is influenced primarily by current climate (rather than historical climate change), by precipitation-related variables (rather than temperature-related ones), and roughly equally by climate extremes and seasonality. Furthermore, a positive relationship between MDR and fern species density is found, with the latter being more strongly directly influenced by MDR than by climate, and all of the above-mentioned patterns differ among longitudinal segments. Critically, the relationship between MDR and climate shifts across longitude, revealing region-specific diversification drivers. This study shows that diversification rates provide complementary information on the evolutionary history of ferns compared to species richness and phylogenetic diversity, and that highly diverse regional fern assemblages appear to be centers of ferns belonging to rapidly diversifying lineages.