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7.7 Proportion of species threatened with extinction

Modified on 2012/11/06 11:26 by MDG Wiki Handbook Categorized as Goal 7


Goal 7. Ensure environmental sustainability Target 7.B: Reduce biodiversity loss, achieving, by 2010, a significant reduction in the rate of loss


The proportion of species threatened with extinction measures the proportion of threatened species expected to go extinct in the near future without additional conservation action. It is an index based on the number of species in each category of extinction risk on the International Union for Conservation of Nature (IUCN) Red List.

This indicator is expressed as an index ranging from 0 to 1.

Threatened species are those listed on the IUCN Red List in the categories as Vulnerable, Endangered or Critically Endangered (i.e. species that are facing a high, very high or extremely high risk of extinction in the wild). Changes over time in the “proportion of species threatened with extinction” are largely driven by improvements in knowledge and changing taxonomy. The IUCN Red List Index (RLI) accounts for such changes and is a more sensitive indicator than the simple proportion of threatened species. It measures change in extinction risk over time resulting from genuine improvements or deteriorations in the status of individual species. It can be calculated for any representative set of species that have been assessed for the IUCN Red List at least twice.

Method of computation
The IUCN RLI is calculated at a point in time by first multiplying the number of species in each Red List Category by a weight (ranging from 1 for ‘Near Threatened’ to 5 for ‘Extinct’ and ‘Extinct in the Wild’) and summing these values. This is then divided by a maximum threat score which is the total number of species multiplied by the weight assigned to the ‘Extinct’ category. This final value is subtracted from 1 to give the IUCN RLI value.

Mathematically this calculation is expressed as:


Where Wc(t,s) is the weight for category (c) at time (t) for species (s) (the weight for ‘Critically Endangered’ = 4, ‘Endangered’ = 3, ‘Vulnerable’ = 2, ‘Near Threatened’ = 1, ‘Least Concern’ = 0. ‘Critically Endangered’ species tagged as ‘Possibly Extinct’ or ‘Possibly Extinct in the Wild’ are assigned a weight of 5); WEX = 5, the weight assigned to ‘Extinct’ or ‘Extinct in the Wild’ species; and N is the total number of assessed species, excluding those considered data deficient in the current time period, and those considered to be ‘Extinct’ in the year the set of species was first assessed.

The formula requires that:
  • Exactly the same set of species is included in all time periods, and
  • The only Red List Category changes are those resulting from genuine improvement or deterioration in status (i.e. excluding changes resulting from improved knowledge or taxonomic revisions).

In many cases, species lists will change slightly from one assessment to the next (e.g. owing to taxonomic revisions). The conditions can therefore be met by retrospectively correcting earlier Red List categorizations using current information and taxonomy. This is achieved by assuming that the current Red List Categories for the taxa have applied since the set of species was first assessed, unless there is information to the contrary that genuine status changes have occurred. Such information is often contextual (e.g., relating to the known history of habitat loss within the range of the species). If there is insufficient information available for a newly added species, it is not incorporated into the IUCN RLI until it is assessed for a second time, at which point earlier assessments are retrospectively corrected by extrapolating recent trends in population, range, habitat and threats, supported by additional information.


The world’s species are impacted by a number of threatening processes, including habitat destruction and degradation, overexploitation, invasive alien species, human disturbance, pollution and climate change. This indicator can be used to assess overall changes in the extinction risk of sets of species as a result of these threats and the extent to which threats are being mitigated.

The IUCN RLI value ranges from 1 (all species are categorized as ‘Least Concern’) to 0 (all species are categorized as ‘Extinct’). An intermediate value indicates how far the set of species has moved overall towards extinction. Thus, the IUCN RLI allows comparisons between sets of species in both their overall level of extinction risk (i.e. how threatened they are on average), and in the rate at which this risk changes over time. A downward trend in the IUCN RLI over time means that the expected rate of future species extinctions is worsening (i.e. the rate of biodiversity loss is increasing). An upward trend means that the expected rate of species extinctions is abating (i.e. the rate of biodiversity loss is decreasing), and a horizontal line means that the expected rate of species extinctions is remaining the same, although in each of these cases it does not mean that biodiversity loss has stopped. An upward IUCN RLI trend would indicate that the MDG target of significantly reducing the rate of biodiversity loss may have been met. An IUCN RLI value of 1 would indicate that biodiversity loss has been halted.


National agencies producing IUCN RLI data include non-governmental organisations (NGOs), government and academic institutions working jointly and separately. Data are gathered from published and unpublished sources, species experts, scientists, and conservationists through correspondence, workshops, and electronic fora. Data are submitted by national agencies to IUCN, or are gathered through initiatives of the IUCN Red List Partnership, which includes: BirdLife International; Botanic Gardens Conservation International; Conservation International; NatureServe; Royal Botanic Gardens, Kew; Sapienza University of Rome; Texas A&M University; Wildscreen; and Zoological Society of London.

Most countries of the world have initiated programmes to assess the status of their species using IUCN Red List Categories and Criteria. These countries will be able to implement the IUCN RLI based on national extinction risk, once they have carried out at least two national Red Lists using the IUCN system in a consistent way. A few countries have completed national RLIs for selected taxa.


This indicator can be disaggregated by ecosystems, habitats, geographic divisions, taxonomic subsets (e.g. families), suites of species relevant to particular international treaties or legislation, and by species that are exposed to particular threatening processes. In each case, information can be obtained from the IUCN Red List to determine which species occur in particular ecosystems, habitats, and geographic areas of interest.

Changes in the RLI are calculated for subsets of species, excluding those genuine status changes among subsets of species that were driven by processes operating outside the ecosystem/habitat/country.


There are four main sources of uncertainty associated with IUCN RLI values and trends.

(a) Inadequate, incomplete or inaccurate knowledge of a species’ status. This uncertainty is minimized by assigning estimates of extinction risk to categories that are broad in magnitude and timing.

(b) Delays in knowledge about a species becoming available for assessment. Such delays apply to a small (and diminishing) proportion of status changes, and can be overcome in the IUCN RLI through back-casting.

(c) Inconsistency between species assessments. These can be minimized by the requirement to provide supporting documentation detailing the best available data, with justifications, sources, and estimates of uncertainty and data quality, which are checked and standardized by IUCN through Red List Authorities, a Red List Technical Working Group and an independent Standards and Petitions Sub-committee.

(d) Species that are too poorly known for the Red List Criteria to be applied are assigned to the Data Deficient category, and excluded from the calculation of the IUCN RLI. For birds, only 0.8 per cent of extant species are evaluated as Data Deficient, compared with 24 per cent of amphibians. If Data Deficient species differ in the rate at which their extinction risk is changing, the IUCN RLI may give a biased picture of the changing extinction risk of the overall set of species. The degree of uncertainty this introduces can be quantified once a significant proportion of Data Deficient species have been re-assigned to other Red List Categories and then reassessed.

The main limitation of the IUCN RLI is related to the fact that the Red List Categories are relatively broad measures of status, and the IUCN RLI can practically be updated only every four years. The IUCN RLI captures trends in one particular aspect of biodiversity: the rate at which species are moving towards or away from extinction. However, biodiversity encompasses a much wider spectrum, from genes, through populations and species, to ecosystems. In addition, the IUCN RLI does not capture particularly well the deteriorating status of common species that are declining slowly as a result of general environmental degradation.

A complementary indicator could be one that uses estimates of population trends in selected species to measure biodiversity loss as the reduction of populations and the relative effectiveness of measures to reduce or reverse these.


See “GENDER EQUALITY ISSUES” for Indicator 7.6 for considerations of gender and biodiversity.


The UNEP World Conservation Monitoring Centre (UNEP-WCMC) is the agency in charge of publishing and monitoring the global figures for this indicator. The International Union for the Conservation of Nature (IUCN) Red List Index (RLI) is used as the basis for calculating this indicator.

The Red List Categories and Criteria and associated documentation for each species on the IUCN Red List are determined globally and provided principally by the Specialist Groups and stand-alone Red List Authorities of the IUCN Species Survival Commission (SSC), the BirdLife International partnership, IUCN Secretariat-led initiatives, and the other IUCN Red List partner organizations. The staff of the IUCN Global Species Programme compile, validate and curate these data, and are responsible for publishing and communicating the results.

Red List assessments are made, either through open workshops or open-access web-based discussion fora. Assessments are reviewed by the appropriate Red List Authority (an individual or organization appointed by the IUCN SSC to review assessments for specific species or groups of species) to ensure standardization and consistency in the interpretation of information and application of the criteria. A Red List Technical Working Group and the IUCN Red List Unit work to ensure consistent categorization between species, groups and assessments. Finally, a Standards and Petitions Sub-committee monitors the process and resolves challenges and disputes over Red List assessments.

The IUCN RLI can be applied at global, regional, and national scales. Global IUCN RLIs are based on repeated assessments of species’ extinction risk at the global scale. While they can be disaggregated to show trends for species at smaller spatial scales, the reverse is not true. National or regional IUCN RLIs cannot be aggregated to produce IUCN RLIs showing global trends. This is because a taxon’s global extinction risk has to be evaluated at the global scale and cannot be directly determined from multiple national scale assessments across its range (although the data from such assessments can be aggregated for inclusion in the global assessment).

The IUCN publishes guidelines on applying the IUCN Red List Categories and Criteria at regional or national scales. If all species within a particular region or country have been assessed at least twice using the IUCN approach, an IUCN RLI can be calculated from national data.

The global IUCN Red List is updated annually. IUCN RLIs for any sets of species that have been comprehensively reassessed in that year are usually released alongside the update of the IUCN Red List. Data stored and managed in the IUCN Red List database (IUCN’s Species Information Service, SIS) are made freely available for non-commercial use through the IUCN Red List website.




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