TheEDGE of Existence programme is a research and conservation initiative that focuses on species deemed to be the world's mostEvolutionarily Distinct and Globally Endangered (EDGE) species. Developed by theZoological Society of London (ZSL), the programme aims to raise awareness of these species, implement targeted research and conservation actions to halt their decline, and to train in-country conservationists (called EDGE Fellows) to protect them.
EDGE species areanimal species which have a high 'EDGE score', a metric combining endangeredconservation status with the genetic distinctiveness of the particulartaxon. Distinctive species have few closely related species, and EDGE species are often the only surviving member of theirgenus or even highertaxonomic rank. The extinction of such species would therefore represent a disproportionate loss of unique evolutionary history andbiodiversity. The EDGE logo is theechidna.[1]
Some EDGE species, such aselephants andpandas, are well-known and already receive considerable conservation attention, but many others, such as thevaquita (the world's rarestcetacean)[2][3] thebumblebee bat (arguably the world's smallest mammal) and the egg-layinglong-beaked echidnas, are highly threatened yet remain poorly understood, and are frequently overlooked by existing conservation frameworks.[3]
TheZoological Society of London launched the EDGE of Existence Programme in 2007 to raise awareness and funds for the conservation of these species. As of 2024, the programme has awarded fellows funds to help conserve 157 different species in 47 countries.[1] The programme lists key supporters as the Fondation Franklinia, On the EDGE, andDarwin Initiative. Donors include theIUCN,US Fish and Wildlife Service, and numerous non-governmental organisations and foundations.[4]
In 2024, researchers at the programme identified EDGE Zones that make up 0.7% of Earth's surface but are home to one-third of the world's four-legged EDGE species.[5]
The EDGE of Existence programme is centred on an interactive website that features information on the top EDGE species detailing their specificconservation requirements. 70% of the mammals which have been chosen are receiving little or no conservation attention according to the inventors.[6]
EDGE research and conservation is carried out by ZSL researchers, a network of partner organizations and local scientists. An important part of the EDGE programme is a fellowship scheme which provides funding and support to local scientists. EDGE Fellows participate in all phases of a research project. Each project is focused on delivering a conservation action plan. Once the action plan is completed, a meeting is held to make additions and corrections to the document.
Some species are more distinct than others because they represent a larger amount of unique evolution. Species like theaardvark have few close relatives and have been evolving independently for many millions of years. Others like the domesticdog originated only recently and have many close relatives. Species uniqueness can be measured as an 'Evolutionary Distinctiveness' (ED) score, using aphylogeny, or evolutionary tree. ED scores are calculated relative to aclade of species descended from a common ancestor. The three clades for which the EDGE of Existence Programme has calculated scores are allclasses, namelymammals,amphibians, andcorals.
The phylogenetic tree has themost recent common ancestor at the root, all the current species as the leaves, and intermediate nodes at each point of branchingdivergence. The branches are divided into segments (between one node and another node, a leaf, or the root). Each segment is assigned an ED score defined as the timespan it covers (in millions of years) divided by the number of species at the end of the subtree it forms. The ED of a species is the sum of the ED of the segments connecting it to the root. Thus, a long branch which produces few species will have a high ED, as the corresponding species are relatively distinctive, with few close relatives. ED metrics are not exact, because of uncertainties in both the ordering of nodes and the length of segments.
GE is a number corresponding to a species'conservation status according to theInternational Union for Conservation of Nature with more endangered species having a higher GE:
| Conservation status | Code | GE score |
|---|---|---|
| Extinct | EX | — |
| Extinct in the wild | EW | — |
| Critically endangered | CR | 4 |
| Endangered | EN | 3 |
| Vulnerable | VU | 2 |
| Near threatened | NT | 1 |
| Least concern | LC | 0 |
| Data deficient | DD | — |
| Not evaluated | NE | — |
The EDGE score of a species is derived from its scores for Evolutionary Distinctness (ED) and for Globally Endangered status (GE) as follows:
This means that a doubling in ED affects the EDGE score almost as much as increasing the threat level by one (e.g. from 'vulnerable' to 'endangered'). EDGE scores are an estimate of the expected loss of evolutionary history per unit time.
EDGE species are species which have an above average ED score and arethreatened with extinction (critically endangered, endangered or vulnerable). There are currently 564 EDGE mammal species (≈12% of the total). Potential EDGE species are those with high ED scores but whose conservation status is unclear (data deficient ornot evaluated).
Focal species are typically selected from the priority EDGE species. However, they also prioritise species outside these rankings. Such species can also have a very high ED but fall outside the top 100 EDGE rankings. These species are conserved by 'EDGE Fellows', who collect data on these species and develop conservation action plans.[7] Fellows have previously collaborated with institutions like National Geographic and The Disney Conservation Fund.[8][9]
Top 3 ranked species on the 2024 EDGE lists foramphibians,birds,gymnosperms,mammals,ray-finned fish,lepidosaurs,crocodylians,testudines, andsharks and rays:[10]
The only current species with an EDGE median score over 100 are the maidenhair tree and wollemi pine. Examples of Critically Endangered species with very low EDGE median scores, 1 or below due to low evolutionary distinctness, are theAlgerian fir,Visayan warty pig, andpindu. The number of EDGE species varies by taxonomic group. For example, 8 crocodylians are EDGE species, representing more than 30% of crocdylians. Meanwhile 908 amphibians are EDGE species, representing less than 15% of amphibians.[11]
