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Why Is Introducing New Predators So Bad for Native Prey?

Red foxes sure like the smell of a bandicoot.

By Nathan Collins


(Photo: Wikimedia Commons)

Introducing a new predator into an ecosystem can have devastating impacts. Consider, for example, the red fox in Australia. The European-native beasts were introduced in the 1850s, and, today, they roam 75 percent of the continent and threaten 76 different native species, including several critically endangered ones. That racks up serious environmental costs. But why is that? According to a newstudy of the red fox and one of its prey, the long-nosed bandicoot, it’s a simple matter of costs and benefits: Red foxes have little to lose by trying out new prey, while bandicoots have to invest substantial effort to avoid potential new predators.

“We propose that this nexus between the costs and benefits of responding to novel information is different for alien predators and native prey, giving alien predators a novelty advantage over native prey,” University of Sydney and University of New South Wales researchers Jenna Bytheway, Catherine Price, and Peter Banks write in Scientific Reports. “This may explain why some introduced predators have rapid and devastating impacts on native fauna.”

Bytheway, Price, and Banks reached that conclusion after conducting an experiment aimed at testing red foxes’ preference for novel meals versus the usual dinner. They first built 72 sand plots in a remote part of Victoria, Australia, and imbued them with the odor of either long-nosed bandicoots—with which the local foxes had no prior experience—or black rats. Although the local foxes didn’t know black rats either, they had long been a source of food for European red foxes, so in theory these Australian foxes might be more likely to investigate spots that smelled of black rat than those that reeked of bandicoot.

Red foxes have little to lose by trying out new prey.

But, in fact, the opposite proved true: Over three nights, red foxes checked out about 85 percent of the bandicoot-smelling sites, compared with less than 30 percent of the rat sites (and a similar number of control sites, which contained sand but no added odors).

The reason, the researchers propose, has to do with the costs associated with encountering new animals—and how those costs differ for predator and prey. “Investigating unfamiliar prey cues (neophilia) can carry relatively little cost to introduced predators for a potentially large reward,” Bytheway, Price, and Banks write, in which case predators may rapidly switch to a new food source, with potentially devastating impacts on the species in question. For prey, on the other hand, avoiding new species may mean forgoing their usual foraging grounds—a difficult choice, particularly when they don’t yet know whether that new species will eat them.

“In time, naïve prey can develop refined recognition and responses to novel predators, however alien predators displaying neophilia skip over this initial learning stage, giving them an advantage,” the researchers write, “which may help to explain why so many native species rapidly decline after the arrival of alien predators.”