Global variation in relative phylogenetic diversity in butterflies

Taxonomic diversity (TD) and phylogenetic diversity (PD) are two important metrics of biodiversity, but they are often mismatched in many areas across the world. This geographic mismatch, typically identified through assessment of relative phylogenetic diversity (RPD), is associated with climatic conditions and is critical not only to understanding the origin and maintenance of biodiversity but also conservation planning. Here, using a comprehensive data set of butterflies across the world, we explore geographic patterns of RPD and its relationships with climatic factors. Butterfly species assemblages used in this study are species in 12 407 grid cells across the world. We use two different metrics to measure RPD: one directly relating PD to TD (PD $_{dev}$ ) and the other exploring variation on phylogenetic branch length (Mishler's RPD). We find that RPD is higher in humid subtropical and tropical regions, where butterflies originated and maintain many distinct phylogenetic lineages, and is lower in temperate and arid tropical regions as well as in geologically young mountains, where there are fewer major phylogenetic lineages and where regional radiations form clusters of closely related species. The patterns of PD $_{dev}$ and Mishler's RPD are largely similar, but PD $_{dev}$ is more strongly related to temperature, whereas Mishler's RPD is more strongly related to precipitation, suggesting that these metrics capture different ways in which climate influences PD. Overall, areas with higher RPD likely hold higher evolutionary potential than areas with equivalent species richness but lower RPD, so that areas of high RPD would be of particular interest for biodiversity conservation.