What does biodiversity actually do? A review for managers and policy makers

Conservation managers and policy makers must often justify the need for protection of biodiversity. However, results of scientific studies testing for a positive value of biodiversity in terms of community stability and ecosystem function have been complex and inconsistent. We review recent information on the consequences of loss of biodiversity for natural systems. The relationships described vary with scale of interest - for instance, biodiversity at local scales typically has strong effects on ecosystem function, although the opposite relationship is often found at regional scales. These inconsistencies lead to some concern as to whether these relationships can be used to justify biodiversity protection. This is particularly relevant to policy, where holistic protection of biodiversity has most often been mooted and justified. For managers, who most often work to protect single species, communities or ecosystem functions, biodiversity research has failed to address questions of critical concern such as consequences of the loss of rare species or the identification of functional keystone species. For the general public, we believe that the confusion and debate surrounding biodiversity and ecosystem function relationships is in danger of eroding the positive value society places on biodiversity. We further warn that using those relationships in policy documents as justifications for biodiversity protection is fraught with difficulties. Finally, we contend that biodiversity research has largely not addressed issues of concern to conservation managers, and list a set of priorities for relevant research on the consequences of biodiversity loss.