Quantifying Biodiversity: Does It Matter What We Measure?

The pace and severity of the current extinction crisis is unprecedented, and there is a large disparity between the scale of the problem and the available recourses with which to mitigate it. Prioritising conservation efforts is therefore critical. With the extinction of species, we lose not only taxonomic diversity but also the ecosystem services they provide and the evolutionary history represented on the branches of the tree of life from which they subtend. How we value these alternative currencies of biodiversity might influence global conservation strategy and resource allocation. Fortunately, different currencies frequently covary closely, for example, maximising species richness will also do well at capturing evolutionary history. Nonetheless, differences exist at the margins, and these can have significant impact on ordering conservation priorities. Further, costs also vary and some currencies rank similar attributes differently (e.g., extinction risk versus latent risk). Conservation biologists must be prepared for the difficult choices that lie ahead.