Should evolutionary history guide conservation?

Phylogenetic diversity (PD) is an emerging tool for prioritising species in biodiversity conservation problems. PD uses the evolutionary history of a group of species to provide a formal measure of their biodiversity. This provides an objective target for biodiversity conservation, in which decisions are frequently made for political reasons or according to the charisma of a species. Incorporating PD in biodiversity decisions ensures that the best outcome given current knowledge is achieved. Unfortunately, the phylogenetic information required to calculate PD is frequently unknown or costly to obtain. Using PD in a decision making framework also complicates the process substantially, thereby decreasing its transparency and potentially disillusioning stakeholders. Here we provide a broad assessment of the value of PD in biodiversity conservation approaches. We find that using PD in a prioritisation process can typically increase biodiversity outcomes by a broad range of 10-220 %. Higher gains are obtained where (i) few species are selected, (ii) the phylogeny includes speciation events on a broad range of time scales and/or (iii) closely related species are prioritised in the absence of PD (e.g. several closely related charismatic animals). Our results indicate situations where PD is likely to contribute substantially to biodiversity conservation decisions and provides guidance to organisations when deciding whether to incorporating phylogenetic information in their decision making. This assessment is crucial as inclusion of PD may be costly and reduces transparency of the decision process, however the potential gains may far outweigh this cost.