The Timeline of Fear
Two populations of bandicoots show that learning to fear a new predator can take quite some time.
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Somewhere on the outskirts of Hobart, the largest city on Tasmania, a rabbit-sized bandicoot scampers into a backyard. The marsupial begins digging, hunting for truffles. But the bandicoot is itself being hunted: a floppy eared, curly tailed domestic dog gives chase. The bandicoot is completely unprepared, and quickly becomes yet another casualty in Australia’s ongoing battle against introduced predators.
Dogs were first introduced to the island around 200 years ago, and despite years of coexistence, Tasmania’s native bandicoots have not yet learned to see them as threats. It’s puzzling, then, that the bandicoots on Australia’s mainland—that have lived alongside domesticated dogs for a similar length of time—go out of their way to avoid them. It’s a curious situation that raises an interesting question: what factors determine how quickly prey learns to fear a new predator?
Back in 2012, biologists Alexandra J. R. Carthey and Peter B. Banks surveyed Sydney residents, and discovered that homeowners were far less likely to find the telltale diggings of bandicoots in their lawns if they had a dog than if they had a cat or no pets at all. The findings implied that bandicoots fear dogs.
The researchers hypothesized that the mainland bandicoots’ wariness of dogs could be attributed to their long coexistence with dingoes. Dingoes first came to mainland Australia about 4,000 years ago, and, having learned to avoid dingoes, mainland bandicoots translated this fear to dogs. If that’s the case, then it also explains why Tasmania’s bandicoots, which have no history with dingoes, aren’t afraid of dogs.
Now, Carthey and Banks, along with biologist Anke S. K. Frank, have found evidence to support this hypothesis.
Much like their earlier research in Sydney, the team sent surveys to homeowners in Hobart. They found that in Tasmania the presence of a dog in the yard did nothing to dissuade bandicoots’ foraging.
“Tasmania actually has mammalian predators. It has the Tasmanian devil, for example. It has the wedge-tailed eagle, and owls, and things like that. It’s not that bandicoots were so naïve that they’ve never been exposed to any predator,” says Frank. But they haven’t yet learned to recognize domestic dogs and cats as potential threats.
It’s hard to say just how long it takes a prey animal to learn to fear an introduced predator. Two hundred years is clearly insufficient, while 4,000 years has proven long enough. The switch-over point therefore lies somewhere in between.
“It’s encouraging that, over time, native species can learn to recognize new species as predators. But in the meantime, many species have already gone extinct due to predation by cats and foxes,” says Deakin University ecologist Tim Doherty, who wasn’t involved in the study.
Invasive predators have been responsible for about 60 percent of extinctions. Natural selection doesn’t always work rapidly enough to counter the threat of a new predator. “We really need to be doing other things to help these native species persist in the meantime,” says Doherty.