How Far Should Humans Go to Help Species Adapt?

This story originally appeared on Yale Environment 360 and is part of the Climate Desk collaboration."I spent 15 years removing cats from fenced reserves and national parks,” Katherine Moseby was saying. “And then, all of a sudden, I was putting them back in. It felt very strange to be doing that.”It was a hot, intensely blue day in the Australian Outback, about 350 miles north of Adelaide. I was tagging along with Moseby as she checked the batteries on the motion-sensitive cameras that dot Arid Recovery, an ecosystem restoration project she and her husband launched in 1997. The project sprawls over 47 square miles of red earth and scrub. It’s entirely surrounded by a six-foot-tall fence, which is designed to keep out feral cats and foxes.
Inside the main fence is a series of smaller fenced-in paddocks. Several years ago, Moseby decided to start adding cats into some of these. Her reasoning was simple and, in its own way, radical. The outback ecosystem had been so fundamentally changed, that, if the native animals were to survive, they would have to change, too. Perhaps they could be trained to avoid cats, which were introduced to the country by the British colonists and now can be found virtually everywhere in Australia, including most islands.
“A lot of the focus has been on trying to come up with methods of killing cats better,” Moseby, who holds a PhD in reintroduction biology, said. “And we sort of started looking at it from the prey perspective, like, what about if we make prey better? Will that help? Because ultimately coexistence is where we’re trying to get to. We’re not going to ever get rid of every cat in the whole of Australia.” It’s estimated that there are as many as 6 million feral cats in the country, and that they kill some 800 million native animals annually. (Foxes, also introduced by the British, are very nearly as widespread; they are somewhat easier to control, though, because they will more readily eat poison bait.)
Over the last several years, Moseby and her colleagues at Arid Recovery have experimented with two threatened marsupial species: the greater bilby, which looks like a small rabbit with a long nose, and the burrowing bettong, also known as the boodie, which has a squirrel-like face, skinny hind legs, and a long tail. They’ve added a small number of cats to some of the paddocks and then painstakingly recorded the results. The idea is to put enough pressure on the marsupials to produce behavioral or—even better—evolutionary change, but not so much pressure that all the animals wind up dead.
“There’s a lot of evidence to show that evolution can occur over very short time periods, particularly when there’s strong selection,” Moseby observed.

Of course, cats and foxes are already putting strong selective pressure on Australia’s native species—so strong that many are no longer around. Among mammals, the country’s extinction rate is the highest in the world. The lesser bilby—the greater bilby’s cousin—disappeared sometime in the mid-20th century. The crescent-tailed wallaby, the desert bandicoot, and the Lake Mackay hare-wallaby vanished around the same time. All, it’s believed, were done in by introduced predators. The greater bilby, for its part, was once abundant throughout most of Australia; today the total population is estimated at fewer than 10,000. The burrowing bettong was one of the most common animals in the country; it’s now restricted to islands and reserves like Arid Recovery.

One of the reasons cats and foxes have been so deadly is they were abetted by introduced prey. European rabbits were imported to Australia in 1859; they multiplied and spread so quickly that within a few decades the population numbered in the hundreds of millions. Not only did the rabbits compete with native mammals, but also they allowed the number of cats and foxes to similarly explode. The predators could hunt native mammals to extinction and still do just fine.