Top predators’ fear of human ‘super predator’ can impact entire ecosystems

Cougars and other large carnivores are frightening beasts but, according to a new study, the fear these top predators inspire may be matched by their own fear of the human ‘super predator’, causing cascading effects down the food chain.

Globally, humans now kill large carnivores at over nine times the rate they are killed naturally, and new research by a team from Western University and the University of California Santa Cruz (UCSC) demonstrates that top predators, like cougars, have learned to fear the human 'super predator', altering the role of large carnivores in the ecosystem.

These findings by Liana Zanette from Western's Faculty of Science, in collaboration with PhD student Justine Smith and Professor Chris Wilmers from UCSC, and others, were published this week in the Proceedings of the Royal Society B.

Zanette, a professor in Western's Department of Biology, and her colleagues experimentally demonstrated that cougars perceive humans as predators, fleeing at simply hearing humans speaking and consequently feeding less when they think humans are nearby, necessitating their killing more prey to compensate.

"Our previous research has shown that fear itself can shape ecosystems, and the fear large carnivores inspire in their prey helps maintain ecosystem health. These new results indicate that, by frightening top predators, the fear of humans has been superimposed on the natural 'landscape of fear', meaning humans may be distorting ecosystem processes even more than previously imagined," explains Zanette, a renowned wildlife ecologist. "These results thus have critical implications for conservation, wildlife management and public policy."

The team conducted the study on cougars living in rural and suburban areas near Santa Cruz, California. To experimentally test their fearfulness of humans, the team played cougars the sounds of people speaking, in conversation, when cougars visited prey kill sites, using hidden automated speakers and cameras. The cougars almost invariably fled when they first heard humans, either did not return or took longer to do so, and in total over 24 hours spent less than half as long feeding as when exposed to control sounds (frogs). This is the first experimental demonstration that large carnivores fear humans as predators, and verifies previous results indicating that cougars kill a third more prey (deer) where they are more frequently frightened by the human ‘super predator’.

Large carnivore numbers have declined worldwide as a result of hunting and persecution by humans, and habitat loss. 

Legal protections and conservation initiatives have reversed these declines in many parts of North America and Europe and large carnivores increasingly inhabit human-dominated landscapes, evidently living in fear, surrounded by the human 'super predator'.


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