How fear drastically shapes ecosystems: Best ideas of the century

When wolves were reintroduced to Yellowstone National Park in 1995, the effects were dramatic. Among other things, elk numbers have declined much more than expected.

It turns out that the simple fear of wolves had a big impact. In places where elk thought wolves might be present, they spent much more time monitoring them, leaving them less time to feed. In an article published in 2001, biologist John Laundré, who died in 2021, used the term “fearscape” to describe this effect.

The idea was not entirely new. Previous laboratory experiments had shown that fear of predators alone could affect prey. Yet the prevailing view at the time was that predators only affected wild prey populations through direct predation. Observations by Laundré and others suggested that this was false, but they did not demonstrate causality.

That’s what Liana Zanette of Western University in Ontario, Canada, did through a series of experiments over the past two decades. In British Columbia, Zanette and colleagues released recordings of predators near wild song sparrows. Fewer eggs were laid, fewer hatched, and fewer hatchlings survived. Overall, less than half of those who lived compared to those who played non-predatory sounds. In in other words, fear can have aand even a greater impact than direct predation.

It’s all about the food, says Zanette. In addition to spending more time watching for predators, prey avoid certain areas altogether, she says, “even though it might be the best food in town.”

This concept of a fear landscape is extremely important because of its ripple effects on ecosystems. In many places on the west coast of Canada, for example, humans have eliminated bears, cougars and wolves that prey on raccoons. These raccoons now spend a lot of time on the shore looking for food like crabs.

When Zanette’s team went there and played recordings of dogs barking, the raccoons mostly avoided going to the seashore and, when they did, spent much more time searching for predators. This led to a dramatic rebound in the abundance of coastal animals that raccoons prey on. On the other hand, where the team broadcast recordings of seal barking, these effects were not observed.

The landscape of fear is essential to fully understanding the impact of humans on wildlife. In one study, Zanette and her team used camera traps to film how wildlife responded to sounds in South Africa’s Kruger National Park. “The fear of lions should be at its peak there,” she says, “but we found that humans were twice as frightening.” »