24. Feb, 2016

Fear of large predators may affect the food chain.

Fear of large predators living in the wild was one of the reasons why humans have attempted and largely succeeded in extirpating many large predators on the planet. But apex predators play a critical role in conserving biodiversity. Marine biologists call this ‘ecosystem service’.*  Since apex predators are op top of the food chain, their presence affects not only the smaller  predators (their potential prey), but also the species at lower levels of the food chain. It’s probably not only the physical presence, but also the fear of a larger predator (e.g. a wolf or a big dog) that prevents smaller predators  (a  raccoon) to start foraging on their favorite prey (a small crab) in certain territories. Which of course  is advantageous for their prey, but not so advantageous for the crabs potential victim (a sea snail) at  a lower level of the food chain. Biologists call this a trophic cascade (see the picture above).

The hypothesis that fear could affect the cascade in the food chain was recently tested by Canadian biologists from  he University of Victoria, BC, Canada*. They  investigated if fear of dogs could change foraging by raccoons living on coastal Gulf Islands in BC,  in particular their foraging on marine  species as crabs and small fishes living in the tidal ponds along the shoreline (the dog is the raccoons old enemy). But they also  looked at effects further down the cascade: on the crabs favorite food. They did  not use real dogs, but playbacks of dog barking and howling , and compared those with non-predator sounds of harbor seals. Using month-long  playbacks, the dog barking (but not the sounds of seals)  drastically reduced raccoon foraging to the benefit of its potential prey (crabs an little fish), but at the cost of their prey the snails.The amount of little fish and crabs in the tidal zones returned to that of islands where raccoons don’t exist.

The investigators conclude that their findings could be important for  conservation of wildlife,  in particular of the large carnivores and their role in  re-establishing  a ‘landscape of fear’.**

*Justin P. Suraci  et al. Fear of large carnivores causes a trophic cascade. Nature Communications.  (23 Feb 2016)

**Laundre, J. W et al. Wolves, elk, and bison: reestablishing the ‘landscape of fear’ in Yellowstone National Park, U.S.A. Can. J. Zool. 79, 1401 (2001)