Phylogenetic Diversity Across the Complete Tree of Life

Abstract

In the face of rapid biodiversity loss, many approaches have been developed to measure biodiversity in ways that go beyond species richness. One prominent example is Phylogenetic Diversity (PD), which measures evolutionary history by summing the branches required to connect a set of species on a dated phylogenetic tree. PD may also capture other biodiversity measures by proxy such as the richness of biological features and their potential future benefits for humanity, sometimes known as ‘future options’. The total global PD is known for some well-studied groups, such as most vertebrates, but PD estimates are lacking for the majority of the tree of life. Here, we characterize the distribution of PD across the complete tree of life with over 2.2 million species. To do this we use data from the Open Tree of Life and a smoothing method to interpolate between nodes without date information. We estimate that the PD represented by all described species together is between 29 and 33 trillion years. We characterize the distribution of evolutionary distinctiveness, a measure of the fair share of PD captured by individual species, across all life and within selected clades. Many clades have bimodal distributions of evolutionary distinctiveness across species which may be due to changes in diversification rate within subclades. PD has previously been used as the basis for conservation prioritization schemes such as EDGE (Evolutionary Distinct and Globally Endangered) which synthesizes phylogenetic tree data with extinction risk data from the IUCN Red List of threatened species. Here we estimate EDGE scores for over 130,000 species, many more than have been done previously. The top EDGE species is Latimeria chalumnae, the critically endangered West Indian Ocean coelacanth. We hope this work will pave the way for more complete and automated analyses of PD and EDGE scores across the complete tree of life.