Biologists have come up with an improved method of prioritising conservation efforts based on how unique a species is and how endangered its relatives are
28 February 2023
The mountain pygmy possum of Australia, the aye-aye of Madagascar and Leadbeater’s possum of Australia are the top three mammals that we should try to save, according to an improved method for prioritising which species to conserve developed by the Zoological Society of London (ZSL).
In 2007, researchers at ZSL proposed that species should be prioritised based on how unique they are, as well as how threatened they are. They developed a method called EDGE, which stands for evolutionarily distinct and globally endangered.
The idea is that it is more important to save different branches on the tree of life than different twigs on the same branch. We lose more when species with no close relatives go extinct than we do when species with lots of close relatives go extinct.
“It’s been quite successful,” says Rikki Gumbs at ZSL. For instance, in 2018, the EDGE list of reptiles highlighted the uniqueness of Australia’s turtles, such as the Mary River turtle (Elusor macrurus), which diverged from other living species 40 million years ago. This has led to more being done to protect them, he says.
But some issues with EDGE have arisen. For instance, we know so little about some species that biologists often have to make guesses when trying to calculate an EDGE score, says Gumbs. And if a species has close relatives that are highly endangered, it should be prioritised over other species whose close relatives aren’t endangered, he says.
So Gumbs and his colleagues have developed an improved version of EDGE that better takes account of uncertainties and factors such as how endangered relatives are, and have applied initially it to mammals.
The improved system doesn’t make much difference to the top 100 – it still includes 97 of the same species, though in a different order. On the 2007 EDGE list of mammals, the mountain pygmy possum (Burramys parvus), the aye-aye (Daubentonia madagascariensis) and Leadbeater’s possum (Gymnobelideus leadbeateri) were ranked 28, 16 and 54 respectively, and these revised rankings are due partly to changes in our knowledge rather than the modified technique.
But the new method does make a big difference further down the rankings. “Forty per cent of species that would previously be recognised as EDGE are not now,” says Gumbs.
The baiji or Yangtze river dolphin (Lipotes vexillifer) topped the first EDGE list. It is now thought to be extinct.
Sign up to Wild Wild Life, a free monthly newsletter celebrating the diversity and science of animals, plants and Earth’s other weird and wonderful inhabitants
More on these topics: