Measuring the changing state of nature

Most attempts to quantify the impact of humanity on nature and bring it to public attention have centred around estimates of extinction rates. Suggestions that these figures have been exaggerated are, in our view, misplaced, but extinction rate estimates do face other problems - inevitable uncertainty, an arguably weak link to economic value, and insensitivity to short-term change. We therefore look here at other large-scale measures of the changing state of nature, focusing on recent analyses of trends in population size, numbers of populations and habitat extent. In spite of being limited by sampling inadequacies, these data provide a sensitive short-term complement to the long-term perspective gained from considering extinction rates that can be linked directly both to economic values and to public concerns. Although further work is needed on extinction rates, we conclude that significant new emphasis should be placed on instituting broader, more systematic monitoring of habitats and populations.