Linking indices for biodiversity monitoring to extinction risk theory

Abstract

Biodiversity indices often combine data from different species when used in monitoring programs. Heuristic properties can suggest preferred indices, but we lack objective ways to discriminate between indices with similar heuristics. Biodiversity indices can be evaluated by determining how well they reflect management objectives that a monitoring program aims to support. For example, the Convention on Biological Diversity requires reporting about extinction rates, so simple indices that reflect extinction risk would be valuable. Here we develop three biodiversity indices that are based on simple models of population viability that relate extinction risk to abundance. The first index is based on the geometric mean abundance of species. A second uses a more general power mean. A third integrates both the geometric mean abundance and trend. These indices require the same data as previous indices, but they also relate directly to extinction risk. Field data for butterflies and woodland plants, and experimental studies of protozoan communities show that the indices correlate with local extinction rates. Applying the index based on the geometric mean to global data on changes in avian abundance suggests that the average extinction probability of birds has increased approximately 1% from 1970 to 2009.