Red List Methodology

How many species are threatened in a region? How vulnerable is a particular species to extinction? What specific threats does it face? These are some of the questions that the IUCN Red List answers.

The IUCN Red List is the world's most comprehensive record on the conservation status of plant and animal species. Using a set of scientific criteria, it evaluates the extinction risk of threatened AND non-threatened species, and compiles information about their ecology, population trends, geographical distribution, threats, uses, conservation measures taken or needed, and of course, the Red List categories.

Global, Regional and National Red Lists

The Global Red List assesses the conservation status of species at international level, whereas Regional and National Red Lists evaluate the risk of extinction within a specific region or country. Thus, one species could have different categories in the Global Red List and in a Regional Red List. For example, a particular species common worldwide and considered as Least Concern (LC) on the Global Red List, could face a high level of threat in a particular region, where it will be evaluated as Endangered (EN).

Guidelines for Application of IUCN Red List Criteria at Regional Levels should be used for each regional or national Red List, in order to avoid an over- or under-estimation of the regional risk of extinction of species.

The Red List Process

In the Mediterranean region, the process of Red Listing is generally as follows:

  • Definition of a preliminary list of species or taxa to be evaluated.
  • Preliminary assessment and mapping based on existing scientific literature, and introduction of data into the IUCN species database.
  • Identification of key regional and national scientists with knowledge of the species group.
  • Expert consultation to review and complete the draft species reports generally through regional workshops (1-5 days and up to 40 participants depending on the number of species to evaluate).
  • Updating the assessments based on experts’ comments.
  • Publication of the species evaluation results – Internet and/or publication.
  • Regular review and update using the scientific network of experts established by the process. 

Red List Categories

There are nine categories in the IUCN Red List system, from species that are not threatened (Least Concern) to species already extinct (Extinct). At regional level, two additional categories are used (Extinct in the region and Not Applicable, for example for non-native species). The threatened categories (Vulnerable, Endangered and Critically Endangered) are based on five scientific criteria that evaluate the risk of extinction of the species based on biological factors such as: rate of decline, population size, area of geographic distribution, degree of population, and distribution fragmentation. These criteria can be applied to all species (except micro-organisms) in all regions and all countries.

UICN Med, Medoffice, Red List, Categories

Structure of the Red List Categories

Photo: IUCN

Red List Criteria

Categories are assigned using five scientific criteria that evaluate the risk of extinction of the species, based on biological factors, such as population declines and range size.