Phylogenetic diversity and conservation evaluation: Perspectives on multiple values, indices, and scales of application

Abstract

"Phylogenetic diversity" and its abbreviation "PD" have now become popular terms describing a fundamental aspect of biodiversity based on phylogeny. After more than 25 years of work on PD (following the 1992 paper in Biological Conservation), methods and applications have explored a wide range of taxonomic groups and geographic scales. PD provides a way to address biodiversity at the level of features or characteristics of species, based on its well-corroborated model linking phylogeny and feature variation. The quantification of feature diversity justifies PD as a measure of option value - the value of living variation in keeping options open for society. This justification for PD in biodiversity conservation gives attention to often-neglected arguments for the value to society of biotic diversity. These largely global option values are complemented by the "insurance" value of PD at the local ecosystem scale. Microbial applications of PD, particularly in human health studies, have successfully implemented a range of PD calculations, including PD dissimilarities among samples. Reduced microbial PD in the human body may indicate reduced resilience, and it is now associated with many human diseases. "Macrobial" ecology has been less successful in integrating PD into a consistent coherent approach. Here, the traditional recognition of many "diversity" indices has been extended to phylogeny. PD as a "biodiversity" measure is confounded with the multitude of phylogeny-based diversity indices describing various ecological factors. Greater integration among the different areas of PD application could better establish PD as a core biodiversity measure, with a shared toolbox providing a range of PD-related calculations.