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When is a species "Extinct"?

Extinction of a species is difficult to detect, yet there are important conservation consequences of classifying an extant species as extinct or an extinct species as extant, and potentially significant costs of making the wrong classification. Given these costs, when should a species be listed as Extinct (EX) on the IUCN Red List? A series of three papers (the "Extinction Trilogy") explores this question.

Paper I (Keith et al.) presents a structured method to estimate the probability that a species is extinct, P(E), based on qualitative and, where available, quantitative information about the severity, duration and scope of threats and their interaction with the species' life history traits that determine its susceptibility to these threats.

Paper II (Thompson et al.) presents an iterative model to estimate the same probability, based on a time series of records of the species, and the timing, comprehensiveness and adequacy of any targeted surveys designed to detect the species after the last known record.

Paper III (Akçakaya et al.) reviews the potential costs and benefits of classifying extinct and extant species; and proposes a framework for setting thresholds of P(E) for classifying species as extinct, possibly extinct, and extant.

Taken together, these papers will allow developing a set of guidelines that will bring greater consistency to how species are listed on the IUCN Red List. Consistent listings will improve our assessment of the extinction rates and reduce costs of incorrect classifications.

References:

Akçakaya, H.R., D.A. Keith, M. Burgman, S.H.M. Butchart, M. Hoffmann, H.M. Regan, I. Harrison, E. Boakes. 2017. Inferring extinctions III: a cost-benefit framework for listing extinct species. Biological Conservation (in press)

Keith, D.A., S.H.M. Butchart, H.M. Regan, I. Harrison, H.R. Akçakaya, A.R. Solow, M.A. Burgman. 2017. Inferring extinctions I: a structured method using information on threats. Biological Conservation (in press)

Thompson, C.J., V. Koshkina, M.A. Burgman, S.H.M. Butchart, L. Stone. 2017. Inferring extinctions II: a practical, iterative model based on records and surveys. Biological Conservation (in press)