Collective analyses on “red-listed species” may have limited value for conservation ecology
While reading, reviewing and citing conservation papers during the last two decades, I have frequently noticed ecological analyses that are based on collective metrics of species of conservation concern. Field studies in particular often relate the number of regionally red-listed (threatened) species found to environmental factors, sometimes using complex multifactor models. Obviously, the occurrence of threatened species supports management decisions and attracts wider public, and ecological analyses of such occurrences may inform us about some threats (e.g., in poorly known ecosystems) or short-term effectiveness of certain conservation management practices (e.g., Flather et al. 1998; Pykälä et al. 2006; Olsson et al. 2014). However, I suspect that a common reason for using collective metrics is inadequate sample size for species-level treatment combined with a lack of critical attitude to the ecological meaning of the analysis. There are both conceptual and practical problems with the ecological relevance of collective threatened-species approaches, which, when unrecognized, may lead to misinterpretation and misuse of the study in conservation management. In addition to general conceptual problems common to any collective indices (e.g., Landres et al. 1988), there are at least four specific issues. First, lists of threatened species (red lists) are snapshots in time that are based on fragmentary knowledge on species and threats, and often include indirect proxies and subjective interpretation (Isaac et al. 2004; Maes et al. 2015). The set of species included (and thus any collective ‘ecological’ relationships reported) can significantly change over years, along with emerging new threats and accumulating knowledge. It may become increasingly difficult to distinguish out-of-date analyses and to communicate that to practitioners. Secondly, the habitat-reduction considerations behind red-listing