Summary
Quantitative thresholds for population size, decline and range classify species from Least Concern to Extinct.
In depth
Criteria A to E consider population reduction, geographic range, small population size, very small population and quantitative analysis. Species are assessed by experts with data and thresholds.
Red List assessments are updated regularly. Data deficient species lack information. Assessments guide policy and funding.
Key idea: classification is based on population trends, size and range.
The IUCN Red List assesses extinction risk using five quantitative criteria: A, population reduction over 10 years or three generations; B, small or fragmented geographic range with decline; C, small population size with decline; D, very small or restricted population; and E, quantitative analysis showing probability of extinction.
A species is placed in a category depending on how strongly it meets thresholds: Critically Endangered (for example, a decline of over 80 to 90 percent, or fewer than 250 mature individuals), Endangered and Vulnerable form the threatened categories. Others are Near Threatened, Least Concern, Data Deficient and Not Evaluated, plus Extinct and Extinct in the Wild. Assessments are reviewed regularly.
Example: the African elephant is now listed as two species, both threatened.
Key idea: the list measures risk, not rarity alone.
Frequently asked questions
What is IUCN Red List Criteria?
Quantitative thresholds for population size, decline and range classify species from Least Concern to Extinct.
Which area of biology covers IUCN Red List Criteria, and how advanced is it?
IUCN Red List Criteria is one of the 52 topics in Taxonomy & Biodiversity. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Endangered Species, Extinction Rate Estimation, Endemic Species.
Can you give an example of IUCN Red List Criteria?
A decline of over 80 percent in 10 years qualifies as Critically Endangered under criterion A.
What should I learn before IUCN Red List Criteria?
Work through the Beginner topics in Taxonomy & Biodiversity first, such as Taxonomy, Binomial Nomenclature, Taxonomic Hierarchy, then return to IUCN Red List Criteria. Advanced topics assume the Intermediate vocabulary.
What topics are related to IUCN Red List Criteria?
The closest topics to IUCN Red List Criteria are Endangered Species, Extinction Rate Estimation, Endemic Species, Minimum Viable Population. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand IUCN Red List Criteria?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for IUCN Red List Criteria. To practise the whole of Taxonomy & Biodiversity, use the Taxonomy & Biodiversity quiz.
How is IUCN Red List Criteria different from Endangered Species?
IUCN Red List Criteria: Quantitative thresholds for population size, decline and range classify species from Least Concern to Extinct. Endangered Species: Species at high risk of extinction, listed on the IUCN Red List. Read both side by side and note what each one explains.
How should I study IUCN Red List Criteria step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Endangered Species and explain the difference aloud. Finally, take the Taxonomy & Biodiversity quiz and come back to this page for any question you miss.