The IUCN Red List of Threatened Species provides taxonomic, conservation status and distribution information on taxa that have been globally evaluated using the IUCN Red List Categories and Criteria. This system is designed to determine the relative risk of extinction, and the main purpose of the IUCN Red List is to catalogue and highlight those taxa that are facing a higher risk of global extinction (i.e. those listed as Critically Endangered, Endangered and Vulnerable). The IUCN Red List also includes information on taxa that are categorized as Extinct or Extinct in the Wild; on taxa that cannot be evaluated because of insufficient information (i.e. are Data Deficient); and on taxa that are either close to meeting the threatened thresholds, or that would be threatened were it not for an ongoing taxon-specific conservation programme (i.e. are Near Threatened or Lower Risk).
Taxa that have been evaluated to result in the lowest threat of extinction are classified as Least Concern. The Least Concern assessments did not appear on IUCN Red Lists produced before 2003 (except for 225 cases in 1996), because the main focus has been on threatened species. However, for the sake of transparency and to place threatened assessments in context, all Least Concern assessments are now included. Unfortunately, there has not been a formal reporting process in place to capture all Least Concern assessments; hence the list provided is incomplete. A process to capture the Least Concern listings has begun (at the species level only), but this is likely to take several years to complete. In-depth analyses of the data contained in the IUCN Red List are conducted periodically and the results are published once every four years.
Summary of categories
For ease of reference, the IUCN categories as of 2012 are set forth in bullet form:
- Extinct (EX) – No known individuals of the taxon extant.
- Extinct in the Wild (EW) – Known only from captive individuals, or as a naturalized population outside its historic native range.
- Critically Endangered (CR) – Extremely high risk of extinction..
- Endangered (EN) – High risk of extinction.
- Vulnerable (VU) – High risk of endangerment in the wild.
- Near Threatened (NT) – Likely to become endangered in the near future.
- Least Concern (LC) – Lowest risk. Does not qualify for a more at risk category. Widespread and abundant taxa are included in this category.
- Data Deficient (DD) – Data inadequate to assess risk of extinction.
- Not Evaluated (NE) – Has not yet been evaluated against the criteria
Statistics for 2012
In the 2012.1 edition, the Red List includes 63,837 species, of which ~30% were found to be threatened (statuses CR + EN + VU). Not all taxonomic groups represented in the list have been fully evaluated, and the number of species found to be Data Deficient varies from group to group. Detailed assessment statistics are available on the IUCN website, broken down by year, status and taxonomic group.
Critique of the IUCN Red List
While the framework of the IUCN provides a valuable starting point for worldwide classification of species for conservation purposes, there have been several criticisms of the IUCN formalism. Chief concerns have been the inadequate documentation of taxon findings and the failure to classify certain taxa which are widely known to be of very low population levels and hence at risk.
- S. H. M. Butchart, et al.. "Going or gone: defining 'Possibly Extinct' species to give a truer picture of recent extinctions" (pdf). Bull. B.O.C. 2006 126A
- International Union for Conservation of Nature www.iucn.org
- N. Mrosovsky. 1997. "IUCN's credibility critically endangered". Nature 389 (6650): 436
- Hugh P. Possingham et al. 2002. "Limits to the use of threatened species lists". Trends in Ecology & Evolution 17 (11): 503–507