Conserving the Tree of Life

Ever heard of the long-eared Gymnure (a relative of hedgehogs) which is thought to resemble some of the earliest mammals? Or the chronic alcohol-consuming pen-tailed treeshrew? Have you fallen in love with the red pandas here at Indianapolis Zoo? Or our aardvark? What these creatures have in common is that they are all evolutionarily distinct; they represent a unique and irreplaceable part of the world’s natural heritage. In short, if we lose these species, there is nothing else like them in the world.  

Sadly, many of these weird and wonderful species are also threatened with extinction. Since 2007, the Zoological Society of London (ZSL) established a metric to prioritize these evolutionarily distinct and globally endangered species for conservation – the EDGE metric. This metric combines a species’ unique contribution to evolutionary history with its extinction risk as assessed on the IUCN Red List of Threatened Species. Those species with the highest EDGE scores are then prioritized for conservation action through the EDGE of Existence program, while the program also builds capacity and develops the next generation of conservationists around the world through EDGE Fellowships. 

Now in its 15th year, the EDGE metric has been applied to mammals, birds, amphibians, sharks and rays, reptiles, corals and gymnosperms (such as conifers and cycads). But the science around dealing with uncertainty and accounting for the extinction risk of closely related species has improved since the metric’s inception, and it is therefore getting a revamp this week: meet the new EDGE2 metric! 

EDGE2 updates the previous metric by factoring in the extinction risk of closely related species (termed complementarity) and better-incorporating uncertainty in species’ evolutionary relationships and conservation status. Researchers then applied this new and improved EDGE2 method to the world’s 6,000+ mammal species. The study – published on February 28, 2023 in the journal PLOS Biology – identified the Critically Endangered mountain pygmy possum (Burramys parvus) of Southeastern Australia, representing 25 million years of evolution and Australia’s only hibernating marsupial, as the species topping the EDGE2 list of mammals. Overall, the research identified 645 priority species for conservation. Protecting the 100 highest-ranking species from the EDGE2 list would preserve more than 700 million years of evolutionary history! 

In addition to prioritizing at-risk species, the new EDGE2 approach also identifies species for inclusion on EDGE Watch and Research lists. The EDGE Watch list includes species with high evolutionary distinctiveness that are not currently threatened with extinction. The list includes species such as the aardvark and one of the weirdest species out there, the duck-billed platypus. The EDGE Research list includes evolutionarily distinct species that have not yet been assessed for the IUCN Red List or have been listed as Data Deficient – i.e. we just don’t know enough about these species to assess their true extinction risk, and more research is urgently needed. As you might expect, species on the EDGE Research list are not familiar household names: owl’s spiny rat or long-eared gymnure, anyone? Precisely. 

The importance of safeguarding the Tree of Life – or phylogenetic diversity, a measurement of the evolutionary history captured by a set of species – is being promoted through one of the Task Forces under the umbrella of the International Union of the Conservation of Nature (IUCN) Species Survival Commission (SSC). The IUCN SSC Phylogenetic Diversity Task Force provides leadership, guidance and expertise on including phylogenetic diversity in conservation strategies. Other conservation organizations, such as On The Edge, specifically focus on providing a platform for and conservation funding to evolutionarily distinct species.  

These conservation groups are also just two examples of the many expert groups that our coordinators here at the Global Center for Species Survival routinely engage with. Our Freshwater Conservation Coordinator Dr. Monni Böhm, previously based at ZSL, is a co-author of the new study introducing EDGE2, and she continues to collaborate on EDGE research with her previous colleagues. A fan of the underappreciated and neglected biodiversity, her particular highlight throughout the history of EDGE was the publication of EDGE Reptiles – think punk turtles breathing through their bums and tiny chameleons the size of a fingernail.  

It has been acknowledged that the planet’s evolutionary heritage is a form of biodiversity that ensures options for future generations. The Tree of Life is a storehouse of these potential benefits for humanity. The weird and wonderful species out there are the leaves that deserve special conservation attention. Or, as ZSL scientist Dr. Rikki Gumbs explains, “The variety of life at which we marvel is the product of the shared and unique evolutionary histories of species past and present, yet many of the most evolutionarily distinct species on Earth today are at risk of extinction.” EDGE2 provides us with a robust and coherent framework to prioritize the world’s most evolutionarily distinct species for conservation action. 

This blog was a collaboration between experts at the Global Center for Species Survival, including Freshwater Conservation Coordinator, Dr. Monni Böhm, as well as Zoological Society of London scientist, Dr. Rikki Gumbs.   

Published March 1, 2023