Standards: IUCN Red Data Book categories
The original IUCN Red Data Book threat categories have been widely applied to hundreds of thousands of taxa of animals, plants, and fungi. Note that these categories refer to the conservation status of an organism in the wild, not to its presence in cultivation or captivity.
In 1994, IUCN adopted a revised set of Red List categories prepared by the IUCN Species Survival Commission (SSC). There are eight categories and three sub-categories. Unlike the original IUCN threat categories, these also include a series of criteria (population reduction, extent of occurrence, population size - mature individuals, probability of extinction) used to make the conservation assessment. See IUCN Species Survival Commission, 1994 and Walter & Gillett, 1998 for further details.
Original IUCN threat categories.
Category (code) |
Definition |
| Extinct (Ex) | Taxa not definitely located in the wild during the past 50 years (criterion as used by the Convention on International Trade in Endangered Species of Wild Fauna and Flora). |
| Extinct/Endangered (Ex/E) | Taxa that are suspected of having recently become extinct. |
| Endangered (E) | Taxa in danger of extinction and whose survival is unlikely if the causal factors continue operating. Included are taxa whose numbers have been reduced to a critical level or whose habitats have been so drastically reduced that they are deemed to be in immediate danger of extinction. Also included are taxa that may be extinct but have definitely been seen in the wild in the past 50 years. |
| Vulnerable (V) | Taxa believed likely to move into the 'Endangered' category in the near future if the causal factors continue operating. Included are taxa of which most or all the populations are decreasing because of over-exploitation, extensive destruction of habitat or other environmental disturbance; taxa with populations that have been seriously depleted and whose ultimate security has not yet been assured; and taxa with populations that are still abundant but are under threat from severe adverse factors throughout their range. |
| Rare (R) | Taxa with small world populations that are not at present 'Endangered' or 'Vulnerable', but are at risk. These taxa are usually localized within restricted geographical areas or habitats or are thinly scattered over a more extensive range |
| Indeterminate (I) | Taxa that are known to be 'Endangered', 'Vulnerable' or 'Rare' but where there is not enough information to say which of the three categories is appropriate. |
"Non-threatened" categories |
|
| Insufficiently known (K) | Taxa that are suspected but not definitely known to belong to any of the above categories, because of lack of information. |
| No information (?) | Taxa for which there is no information. |
| Out of danger (O) | Taxa formerly included in one of the above categories, but which are now considered relatively secure because effective conservation measures have been taken, or the previous threat to their survival has been removed |
| Not threatened (nt) | Taxa that are neither rare nor threatened |
1 See World Conservation Monitoring Centre, 1992.
2 The word "threatened" has no official definition within the IUCN Red Data book category scheme; it is generally understood, however, to include taxa that are either 'Endangered', 'Vulnerable', 'Rare', 'Indeterminate', or 'Insufficiently Known.' It should not be confused with the use of the same term by the U.S. Office of Endangered Species, and in other countries, where it has a legal definition.
Reference (Threatened Plants Committee
Secretariat, 1972)
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Last updated: 27 September 2001