Fear of carnivores good for ecosystem health: study

An experiment involving raccoons and speakers emitting the sound of barking dogs on tracts of beaches on British Columbia’s Gulf Islands shows that the fear of large carnivores has a positive impact on ecosystem health. The study led by University of Victoria PhD student Justin Suraci with support of the Raincoast Conservation Foundation is published today in Nature Communications.

Raccoons on the Gulf Islands are devastating populations of crabs and fish in the intertidal zone, and nesting songbirds on land. Suraci and co-researchers Liana Zanette (Western University) and Larry Dill (Simon Fraser University) suspected this was due to raccoons having little to fear. To investigate whether fear of dogs—a top predator since the elimination of wolves, bears and cougars from the Islands almost a century ago—could affect raccoon foraging behaviours along the shoreline, they played threatening dog sounds from speakers along extensive tracts of shoreline for one month.

They found that raccoons reduced their foraging time by 66 per cent. In that period, researchers recorded a 61 percent increase in the abundance of red rock crab and an 81 per cent increase in intertidal fish—a prime target of raccoons.

“Humans have done an excellent job of wiping out large carnivores across the globe and we’re only starting to understand what the ecological consequences of that are,” says Suraci. “One of the major consequences is that when you take away the large carnivores, you get outbreaks of the species that they eat—herbivores like deer and smaller predators like raccoons. So, understanding the ways in which these large carnivores historically kept their prey in check was very important to restoring these ecosystems.”

“What we’ve shown is that we have to consider the behavioural interactions top predators have with their prey and not just the actual predation—the killing and consumption—when we’re thinking about how to restore ecosystems from which large carnivores have been lost,” says Suraci.

Read the full study in Nature Communications here.

High quality images, an infographic and video with full permissions are available at: http://tinyurl.com/zolyr9h

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