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News Release

July 20, 2006

Human Activity Threatens Stability of Food Webs, Study Finds

It’s long been known that human activity is eroding biodiversity. Now a new study by University of Guelph researchers — published today in Nature — reveals that the stability of ecological food webs is also at risk.

The study, headed by Neil Rooney and Prof. Kevin McCann of Guelph’s Department of Integrative Biology, says that complex ecosystems are held together by their top predators — the very species most under threat from humans.

“It’s an important finding,” said Rooney, a post-doctoral researcher. “It indicates that top predators keep food webs in check, and that if you remove them, the systems will unravel.”

He and McCann, along with Guelph master’s student Gabriel Gellner and Colorado soil ecologist John Moore , surveyed data from eight aquatic and terrestrial ecosystems across the world, including Chesapeake Bay, the Alaskan tundra, a European pine forest and a Dutch experimental farm.

It has long been speculated that diverse food webs are more stable than less diverse systems. “We set out to determine whether there are common structures or processes that confer this stability to diverse food webs,” Rooney said.

“Whether we were looking at an aquatic ecosystem or a soil one, a common pattern emerged. Top predators tend to feed on prey that derive their energy from different resources, and therefore act as couplers of what we refer to as energy channels.”

Human interference, such as nutrient pollution as a result of urban development or intensive agriculture, can change the relative importance of these energy channels in food webs, resulting in a loss of both diversity and stability, Rooney said. Moreover, the researchers found that the removal of top predators has negative ramifications that can be observed throughout the entire food web.

“For example, take away the tuna from a marine system, and you’ll release from predation the populations of fish that tuna normally feed on, and this will affect everything from the phytoplankton to the detritus feeders,” Rooney said.

Alarmingly, predators — commonly dominant carnivores — are often more susceptible to human activity than other members of the food web, and Rooney speculates there are numerous reasons, ranging from being perceived as a threat to being a food source.

“When it comes to the reduction of biodiversity as a result of human activity, people often demand evidence that their actions have consequences before taking remedial action, and this paper is a first step towards presenting that evidence.”

In addition to the Guelph study, Nature published a related commentary that argues conserving biodiversity may be an even greater challenge than tackling climate change and suggests an international expert group, similar to the Intergovernmental Panel on Climate Change, be established.