Beyond Species Richness for Biological Conservation

Recent global policy developments have highlighted the need for straightforward, robust, and meaningful biodiversity metrics. However, much of conservation science is dominated by the use of a single metric, species richness, despite several known limitations. Here, we review and synthesize why species richness (i.e., the number of species in a local area) is a poor metric for a variety of topical- and policy-relevant conservation problems. We identify the following three key issues: (1) increasing evidence emphasizes that species richness is often not a robust metric for identifying biodiversity change, (2) species richness ignores species identity and so may often not reflect impacts on species of concern, and (3) species richness does not provide information needed on the persistence of biodiversity or the provision of ecosystem services. We highlight the unappreciated practical outcomes of these limitations with examples from three ongoing conservation debates: whether local biodiversity is declining, how habitat fragmentation affects biodiversity, and the extent to which land sharing or sparing is more beneficial for biodiversity conservation. To address these limitations, we offer a set of guidelines for the use of biodiversity metrics in conservation policy and practice.