IUCN
The IUCN (International Union for Conservation of Nature) classification system categorizes species by extinction risk into nine groups: Extinct (EX), Extinct in the Wild (EW), Critically Endangered (CR), Endangered (EN), Vulnerable (VU), Near Threatened (NT), Least Concern (LC), Data Deficient (DD), and Not Evaluated (NE), with the top three (CR, EN, VU) collectively termed "threatened". This system, used in the IUCN Red List, assesses global extinction risk based on criteria like population size, decline, and range, informing conservation efforts.
IUCN Red List Categories (Highest Risk to Lowest)
Extinct (EX): No known living individuals remain.
Extinct in the Wild (EW): Survives only in captivity or outside its historic range.
Critically Endangered (CR): Extremely high risk of extinction in the wild.
Endangered (EN): Very high risk of extinction in the wild.
Vulnerable (VU): High risk of extinction in the wild.
Near Threatened (NT): Close to qualifying for a threatened category.
Least Concern (LC): Widespread and abundant; low risk.
Data Deficient (DD): Insufficient data to assess risk.
Not Evaluated (NE): Not yet assessed against criteria.
