Assessments of risks to biodiversity, for instance by the IUCN Red List system, often rely on spatial distributions of species and ecosystems. Two spatial metrics commonly used for this purpose are Extent of Occurrence (EOO) and Area of Occupancy (AOO). The use of these spatial metrics in IUCN Red List has been controversial. There have been suggestions that these metrics should be measured at much finer scales or resolutions than those used by IUCN. Two recent papers tested alternative methods of measuring these spatial metrics. AOO:Keith, Akçakaya and Murray (2018) demonstrated that AOO is a remarkably strong predictor of risk. More importantly, the study showed, for the first time, that AOO performs best when measured with grid cells that are only slightly smaller than the size of threatening events such as habitat loss, chemical spills, biological invasions, disease outbreaks, fires and other impacts. Contrary to previous assertions, AOO was a less accurate predictor of risks when measured at much finer scales than those recommended by the IUCN. The best way to measure the area occupied by a species or ecosystem depends on the sizes of threats more than the shape or size of the distributions of species or ecosystems. EOO:Joppa et al. (2016) concluded that measuring EOO as the minimum convex polygon (also known as a convex hull), as recommended by the IUCN, will allow for assessments across species and taxonomic groups to be comparable over space and time and will ensure far greater consistency across the IUCN Red List. Additional issues that has led to misconceptions of the IUCN Red List criteria are discussed by Collen et al. (2016). References: Collen, B., N.K. Dulvy, K. Gaston, U. Gärdenfors, D. Keith, A. Punt, H. Regan, M. Böhm, S. Hedges, M. Seddon, S. H. M. Butchart, M.Hoffmann, S. Bachman, and H. R. Akçakaya. 2016. Clarifying misconceptions of extinction risk assessment with the IUCN Red List. Biology Letters 12: 20150843. https://doi.org/10.1098/rsbl.2015.0843 Joppa, L. N., S. H. M. Butchart, M. Hoffmann, S. Bachman, H. R. Akçakaya, J. Moat, M. Böhm, R. A. Holland, A. Newton, B. Polidoro, and A. Hughes. 2015. Impact of alternative metrics on estimates of extent of occurrence for extinction risk assessment. Conservation Biology 30:362-370. https://doi.org/10.1111/cobi.12591 Keith, D.A., H.R. Akçakaya, N.J. Murray. 2018. Scaling range sizes to threats for robust predictions of risks to biodiversity. Conservation Biology 32:322–332. https://doi.org/10.1111/cobi.12988
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 214:336-342. Keith, D.A., S.H.M. Butchart, H.M. Regan, I. Harrison, H.R. Akçakaya, A.R
Indigo bunting (Passerina cyanea). Photograph taken on 8 May 2016 at East Farm Preserve, New York
Eastern box turtle (Terrapene carolina carolina), Long Island, New York
Yellow-chinned anole (Anolis gundlachi), El Yunque National Forest, Puerto Rico.