Flora of the hot deserts: emerging patterns from phylogeny-based diversity studies

Abstract

Relatively recent increases in molecular and geographic data for many taxa in different areas of the world have provided scientists with tools to evaluate biodiversity using evolutionary or phylogeny-based indices (reviewed by Laffan, 2018). These measures provide quantitative estimates of the portion of the tree of life contained in a taxon or community, aiming to answer the question of what percentage of the phylogeny would be lost if that taxon or community is not conserved (Faith, 1992; Purvis et al., 2000). One of the most widely used phylogenetic indices is phylogenetic diversity (PD), which measures the evolutionary history captured by a set of species (or any biodiversity unit) on the tree of life (Faith, 1992). A higher PD value can represent either a set of taxa that represent longer branches than expected and/or are overdispersed in the phylogeny (Fig. 1A, B). Use of PD was proposed more than two decades ago (Faith, 1992) as a method for finding sets of taxa that could be highlighted as priorities for conservation and has recently been proposed as a biodiversity metric by several international conservation organizations (see IPBES, 2019). For example, the International Union for the Conservation of Nature (IUCN) has recently established a Phylogenetic Diversity Task Force (https://www.iucn.org/commissions/ssc-groups/disciplina ry-groups/phylogenetic-diversity-task-force), a global expert group, aimed at incorporating PD into practical conservation strategies.