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A Critically Endangered (CR) species is one which has been categorized by the International Union for Conservation of Nature (IUCN) as facing a very high risk of extinction in the wild. It is the highest risk category assigned by the IUCN Red List for wild species. As of 2014, there are 2464 animals and 2104 plants with this assessment, compared with 1998 levels of 854 and 909, respectively. As the Red List does not consider a species extinct until extensive, targeted surveys have been conducted, species which are possibly extinct are still listed as critically endangered. IUCN maintains a list〔http://www.iucnredlist.org/about/summary-statistics#Table_9〕 of "possibly extinct" ''CR(PE)'' and "possibly extinct in the wild" ''CR(PEW)'' species, modelled on categories used by BirdLife International to categorize these taxa. ==IUCN definition== To be defined as critically endangered in the Red List, a species must meet any of the following criteria (A–E) ("3G/10Y" signifies three generations or ten years—whichever is longer—over a maximum of 100 years; "MI" signifies Mature Individuals): :A: Occurring over less than 100 km² and two of: ::1. Severe habitat fragmentation or existing at just one location ::2. Decline in extent of occurrence, area of occupancy, area/extent/quality of habitat, number of locations/subpopulations, or amount of MI. ::3. Extreme fluctuations in extent of occurrence, area of occupancy, number of locations/subpopulations, or amount of MI. :B: As above, but less than 10 km² (used to show differing levels of severity). :C: Declining population of less than 250 MI and either: ::1. A decline of 25% over 3G/10Y; ::2. Extreme fluctuations, or over 90% of MI in a single subpopulation, or no more than 50 MI in any one subpopulation. :D: Numbers less than 50 MI. :E: At least 50% chance of going Extinct in the Wild over 3G/10Y. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「critically endangered」の詳細全文を読む スポンサード リンク
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