Fear of predators can trigger a cascade of effects through an ecosystem.

Credit: Shanna Baker/Hakai Magazine

Humans have eliminated most predators of raccoons (Procyon lotor; pictured) — such as cougars and wolves — from the Gulf Islands of British Columbia in Canada. This has allowed the raccoons to forage almost freely on shoreline species such as crabs and fish. To instil fear in the raccoons, Justin Suraci at the University of Victoria in Canada and his colleagues broadcast dog vocalizations over various island shores for one month. They found that foraging by racoons decreased drastically at these locations compared to areas where seal vocalizations were broadcast. This caused the number of some crabs to increase by up to 97% and numbers of some fish to rise by 81%. The snail prey of one crab species saw declines.

This manipulation of fear shows the cascading effects of losing large predators from ecosystems, the authors say.

Nature Commun. 7, 10698 (2016)