In the 1990s, a famous study found that animals in Yellowstone National Park (like elk) bred in fewer numbers and ate less after wolves were re-introduced - which seems like a normal thing to happen when you introduce an apex predator in a new ecosystem. However, what the study pointed out, in fact, was that most of the elk population suffered not as a result of attacks from wolves, but rather simply due to them knowing wolves where now sharing the same park. In other words, fear produced such intense ripples that it altered the entire ecosystem. This was very controversial, and a team of Canadian researchers sought to replicate the findings on an island of fearless raccoons.
In the Gulf Islands, just south of Vancouver, raccoons go about a carefree life. They forage all the time, be it night or day, and can easily be found in forest clearings as if they don't mind anything. These raccoons basically have no idea what life is on the mainland where cousins rarely venture in the daylight and spend a lot of time clinging to trees. It's pretty sweet, I guess, once you stop living in constant fear of suddenly turning into dinner.
Around a hundred years ago all the island's big predators like bears, pumas, and wolves were exterminated by human hunters. Today, the single threat to the perfect raccoon life style are domestic dogs (more often than not, a raccoon will actually wound or kill a domestic dog in a fight).
The circumstances of the Gulf Islands proved to be a perfect ground for Liana Zanette and other colleagues from the University of Western Ontario. Previously, in 2011, Zanette showed that song sparrows in the same island raised 40 percent fewer chicks if they hear the calls of hawks, owls, and other predators through speakers. Being larger mammals, raccoons' behaviour is a lot more interesting to study.
As was the case with the sparrows, the researchers yet again installed speakers throughout areas known to harbor racoons, like the shoreline. For one month, barking sounds were played. The researchers found raccoons became much more vigilant and visited the shoreline 66% less often. The most interesting finding, however, came from the analysis of the underlying ecosystem. There were 81 percent more fish in the rock pools, 59 percent more worms, and 61 percent more red rock crabs, as reported in Nature.
“We did an experiment and showed just what has been claimed in Yellowstone,” said Zanette for The Atlantic. “Introduce fear of predators, and the prey get so scared that they eat less. This actually can happen.”
What this means is that introducing a predator back into the wild can bear far greater consequences that one might think at first glance. That's because the psychological input in the predator-prey relationship is not evident. Even two wolves in an ecosystem with no prior history of such predators could create significant disturbances with their fear instilling howls alone.
Once the Yellowstone study was first released, many advocated that putting species back into the wild would do more harm than good. This has fueled a debate which is still far from settled. What Zanette and colleagues show is that this discussion merits a lot of thought.