Aye-aye and posums are on our list of top mammals that we should focus on

Australia’s mountain pygmy opossum, Madagascar’s aye-aye and Australia’s Leadbeater’s possum are the first three mammals we should try to save, according to an improved method for prioritizing species to be preserved developed by the Zoological Society of London (ZSL).

In 2007, researchers at ZSL suggested that species should be prioritized 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 preserving the different branches on the tree of life is more important than saving the different branches on the same branch. We lose more when species with no close relatives go extinct than when species with many close relatives go extinct.

“It’s been very successful,” says ZSL’s Rikki Gumbs. For example, in 2018, the EDGE List of Reptiles highlighted the uniqueness of Australian tortoises, such as the Mary River tortoise (Elusor macrorus), which diverged from other living species 40 million years ago. This has led to more efforts to protect them, he said.

However, there were some problems with EDGE. For example, we know so little about some species that biologists often have to guess when trying to calculate an EDGE score, says Gumbs. He adds that if a species has relatives that are at high risk, it should be given priority over other species whose relatives are not at risk.

So Gumbs and colleagues developed an improved version of EDGE that takes into account uncertainties and factors such as how close relatives are at risk, and initially applied it to mammals.

The improved system doesn’t make much difference to the top 100 – it still includes 97 of a kind, albeit in a different order. In the 2007 EDGE List of Mammals, the pygmy mountain opossum (Burramys Parvus), and aye-aye (Daubentonia madagascariensis) and leadbetter opossum (Gymnobelideus leadbeaterii) ranked 28th, 16th, and 54th, respectively, and these revised rankings are partly due to changes in our knowledge rather than modified technique.

But the new method makes a huge difference down the line. “Forty percent of species that would previously have been recognizable as EDGE are not now,” says Gumbs.

Baiji dolphin or Yangtze River (Lipotis Fixilver) topped the EDGE list first. It is now believed to be extinct.

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