Holy crab! Fear can be used to restore ecosystems

Fear of being eaten can have as much effect on the food chain as actual predation, a new study shows.

Canadian scientists played dog yelps to wild raccoons, and saw the terrified creatures went out to look for food only a third of their usual foraging time. This meant populations of their favourite food, crabs, shot up – shore crabs doubled in numbers, while red rock crabs increased 61%.

In turn, the crabs' prey and competitors, such as periwinkle snails and staghorn sculpin fish, dropped.

The simple experiment, which was the first to show how top predators such as dogs can affect the whole food chain, was published in Nature Communications.

Raccoons are adept crab-hunters. In a few of the Gulf Islands of British Columbia in Canada, wolves, bears and cougars have long been removed, and the wild raccoons fearlessly go to town on their crustacean meals on the shoreline. They're quite good at it, too.

So University of Victoria biologist Justin Suraci and colleagues put the fear into wild populations on several small islands by playing recordings of dogs, which are kept by people living on the islands, for a month.

When a raccoon ventured out to forage among the rocks, they played a 10-second clip of a barking dog. The raccoons responded either by running away, or staying but being super vigilant.

Cameras captured the raccoons' reaction, which didn't change the entire month. 

The authors write this fear response can be used by ecologists to revive populations of species, such as the red rock crab, without hurting their predators: "Our experimental results support the contention that, when it comes to conserving biodiversity and maintaining healthy ecosystems, fear has its uses."