Phylogeny-based metrics of biodiversity: concepts and methods

The concept of valuing evolutionary history has a long tradition and was formalized by several research groups in the early 1990s, each aiming to capture the products of evolution more comprehensively than species richness alone. Preserving the "Tree of Life" has since become a central, if sometimes contested, goal in conservation biology. Faith's phylogenetic diversity (PD), defined as the sum of the edge lengths of a rooted tree connecting a set of focal entities, is the most widely used metric in this context and underpins an extensive methodological framework. This framework includes widely used species-specific indices such as EDGE, as well as approaches that quantify expected species-specific contributions to PD such as EDGE2. This chapter focuses on the development of this framework of phylogeny-based conservation metrics. We review the development of species-specific indices, highlighting their strengths and limitations, and trace their progression from simple formulations to game-theoretic approaches and more abstract generalizations. We also discuss how these indices are applied in conservation practice, with particular emphasis on the EDGE framework. We further discuss the relationship between the edge lengths of a phylogeny and the evolutionary features they are intended to represent. Finally, we highlight recent advances in the field and identify areas for future research.