To save a species on the brink, look to where its ancestors thrived

The mountain pygmy possum is so rare that it was known only from fossils until 1966, when skiers on Mount Hotham in Victoria, Australia, found one scampering around the woodpile at their ski lodge. That was an ironic twist of fate, since the expansion of ski resorts is one of the threats to the survival of the remaining 2,000-3,000 possums found on just a few Australian mountains today.

Another problem creeping up on the possums (as well as the skiers) is climate change, which freezes some possums in their hibernating burrows as reduced snow cover from warming increases the animals’ exposure to icy winter winds. Increased drought, meanwhile, is causing catastrophic declines in fat-rich bogong moths, one of the mountain pygmy possum’s favorite foods—though they are also very fond of the bright red fruits and tough seeds of the mountain plum pine.

Those challenges put the critically endangered possums at risk of extinction, says paleontologist Michael Archer of the University of New South Wales. “Two consecutive years of reduced snowfall could eliminate this animal from the world,” he says.

Judging from the fossil record, the possums’ direct ancestors were living in lowland wet forests. This inspired a plan, described recently in the journal Philosophical Transactions of the Royal Society B, to move some possums off the mountain and into these rather different habitats to ensure the species’ survival, a proposal not without controversy.

Between 25 and about 15 million years ago, the possums’ closest relatives thrived in the forests, Archer says. In fact, it appears that for most of their existence the ancestors were “always in cool lowland rainforest environments.”

If they once lived there, then why not again?

A really odd tooth

The mountain pygmy possum and its direct ancestors are easily recognized by one very distinct premolar tooth that looks very odd and dangerous, says Archer, “like one half of a circular saw, a big curved tooth with ridges all around its cutting edge.”

The tooth allows today’s possums to crack the tough seeds of the mountain plum pine, and it’s possible that it served a different purpose in the past.

Yet the teeth of the living animal and its ancestors are so similar, says Archer, that “you’d have to be a staggeringly brave paleontologist to say these differences have any functional importance.”

Though they are considered to be different species, Archer believes the fossils track the same animal through time as random genetic variation changes it slightly.

The earlier version of the possum was abundant, says Archer. “So before we write this animal off as an early casualty of climate change, why wouldn’t we try to take a small colony out to breed, then release some of their offspring into the forests their ancestors used to live in?”

Stuck on the edge

All of this begs the question of how the mountain pygmy possum ever got stuck up there. “We’re not entirely sure of that,” Archer admits, “but we know that from about 15 million years ago, Australia became progressively more arid, and the central tropical forests began to dry out, forcing some pygmy possums up into the mountains, and making many others go extinct.”

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As a result the species may today be hanging on at the very edge of its former habitat.

While some wet lowland forests might be very attractive to the possums, Archer says, they have no way of getting there. There is no longer any shelter along the way, as forest corridors have disappeared because of climate change and land-hungry human activities.

“We’re changing the world so fast that many species can’t adapt and keep up. That puts on us the responsibility to step in and find ways to ensure the survival of threatened species that can’t do it on their own,” Archer says.

That’s why Archer and about a dozen colleagues have started a project to breed and hopefully release mountain pygmy possums into select lowland forest areas, “hopefully in a year or two,” he says.

The few animals that are already in what will become the breeding center, as well as some possums housed in sanctuaries, appear to be adaptable, says Archer, feeding on all kinds of food and making babies while skipping hibernation altogether. Even so, the possums will be well-prepared before their release.

“If you suddenly took an animal out of the alpine zone, and immediately released it into a lowland rainforest, you’d have a very confused possum on your hands,” Archer says. “So we’ll get them used to the kinds of resources they’ll encounter in the release areas, such as insects and seeds. And my guess is that they will be immediately exploring and trying them out, to find whether they are edible or not.”

Release with care

Daniel Blumstein is somewhat apprehensive. A behavioral biologist at the University of California, Los Angeles, Blumstein has done research on ways to improve the rehabilitation and reintroduction of rare Australian mammals into areas where they used to occur, but is not involved in this project.

“Expanding the range of a rare species may be a good idea under certain circumstances, but putting an animal into an ecosystem where it has not recently occurred is not without risk,” says Blumstein. “While the climate may be amenable to living there, it’s difficult to know what the negative impacts on other species might be.”

Judging from the fossil record, the mountain pygmy possums’ ancestors shared their very biodiverse habitats with dozens of other mammals, and Archer does not expect them to do any damage to other rare species.

“But we don’t intend to release the animals, then turn our backs on them. We’ll be carefully monitoring the whole thing, as part of the experimental procedure. I only wish Australia’s European colonists had been half as careful before releasing cats, foxes, and rabbits here,” he says.

The mountain pygmy possum is not the first, and unlikely to be the last, animal to benefit from insights gained from the fossil record. In New Zealand, an alpine bird called the takahē was released into the lowlands after a paleontologist pointed out that its ancestors used to dwell there.

Back in Australia, Archer is considering the possibility of moving the western swamp tortoise, whose swamps are now drying out, into the eastern lowland rainforests where one of its ancestors was found. Some have even suggested bringing the Komodo dragon back to the Australian mainland, where its ancestors originated, though that’s likely to prove considerably more controversial than moving a few pygmy possums.