Evolutionarily Distinct and Globally Endangered (EDGE) Index

The EDGE Index tracks the conservation status of the world’s most evolutionarily distinct species, and ranges from 100% when all evolutionarily distinct species are threatened with extinction, to 0% when none are threatened.

The full methodology is available in the 2023 paper published in Conservation Biology.

Global EDGE Index

The Evolutionarily Distinct and Globally Endangered (EDGE) Index allows us to monitor changes in the extinction risk to the world’s most evolutionary distinct species, some of the most irreplaceable and unique species.

The EDGE Index has been calculated for a single time point (2023) for all major vertebrate groups, seed plants, flowering plants, and freshwater crayfish, and this website will be updated as more data becomes available. Additionally, trends have been calculated for groups with available Red List Index data for more than one timepoint, namely amphibians, birds, cycads and mammals. We will update and recalculate the EDGE Index as taxonomic coverage and number of assessment timepoints grow across the Tree of Life. The data to reproduce the global EDGE Index plot for 2023 is available here. Extinction risk data is derived from the IUCN Red List of Threatened Species and Red List Index. Steps and data to calculate the indicator at global and national levels are available below.

*The 2023 timepoints are provisional, based on a combination of Red List Index data (amphibians) and IUCN Red List v2023.2 data (all other clades), and is expected to change with updates to the Red List Index.

EDGE Index the national level

The EDGE Index has been disaggregated to national level for all taxonomic groups. Nationally disaggregated EDGE Index values are available here.

Follow these steps to calculate the EDGE Index at the national level for a given taxonomic group.

Data needed:

  • Global ED Dataset

  • National or global IUCN Red List or equivalent data

Step 1: download the ‘Global ED Dataset’

The EDGE Index tracks the extinction risk of a globally shared set of species that are above median Evolutionary Distinctiveness (ED) within their constituent taxonomic group (monophyletic clade), at the Class or Order level. The Zoological Society of London’s EDGE of Existence programme provides a global set of vertebrate species with information on whether each species is above or below the median ED for use in national-level reporting, which can be downloaded here. This list can be subset to different Classes (or ‘clades’ to enable the independent monitoring of reptile groups). For equivalent data for seed plants, please contact us here.

Step 2: match the species

National taxonomies can vary from global taxonomies for a variety of reasons. Match the species in your national taxonomy to those in the Global ED Dataset as best as possible. >80% congruence is advised for robust reporting.

Step 3: subset to national high-ED species

Once you have your set of national species matched to those in the Global ED Dataset, subset this to the set of national species that are above median ED globally using the “above.median.ED” column. This is the set of species whose extinction risk must be tracked to calculate the EDGE Index.

Step 4: calculate the EDGE Index

For however many current and historical time points for which IUCN Red List or equivalent extinction risk information is available, calculate the proportion of species that are threatened with extinction (Vulnerable, Endangered, Critically Endangered) or have gone extinct (Extinct in the Wild, Extinct) since the first time point. This is the EDGE Index.

If any components of this calculation are not possible or you need support, please contact us here.