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Field Notes

Covering the natural wonders of the Pacific Northwest

August 1, 2011 at 3:45 PM

Big predators: Key to the ecosystem

Turns out large predators have large impacts — so big that the decline of so-called apex predators, ranging from wolves to lions, sharks and sea otters, may represent some of the most powerful impacts humans have ever had on Earth’s ecosystems, a group of 24 researchers concluded in a recent report in the journal Science.

wolf up close.JPG

Top predators, such as wolves, have wide influence, scientists have learned. And that’s true in marine as well as terrestrial ecosystems, from the mountains to the sea, from the tropics the arctic. Everything’s connected.

Photo: Courtesy Yellowstone National Park

A bigger impact than pollution, than development? That’s hard to picture. But so it is, the scientists state, because taking out top predators severely disrupts many other plant and animal species in what scientists call a trophic cascade.

Sandi Doughton, our science writer at The Seattle Times wrote about how this works locally, with the loss of wolves at Olympic National Park. Here’s her story in the Times.

She was writing about researchers at Oregon State University who found

everything from elk populations and vegetation in the park was effected by the loss of wolves, hunted to extinction in the park. Their study posed interesting questions for management of the park, which is not an intact ecosystem without the wolf.

wolf chasing.JPG

No wolves, too many elk. Too many elk, too much browsing. Too much browsing, fewer trees. And so on. What is new is the understanding that this is true across ecosystems, across the globe, from lizards on islands, to jaguars in South America, to large mammals in Africa, to lemmings in the arctic, to sharks in the North Atlantic.

Photo courtesy Yellowstone National Park.

The scientists writing the most recent paper in Science made this poignant point: We are in the middle of a sixth wave of massive extinction, and it is different than the other previous ones in that it is largely caused by a single species: homo sapiens. Further, the destruction is the result of a something more subtle than pollution out of a pipe or smokestack, or paving of habitat. It’s the destruction of the myriad interactions between animals and plants and ecosystems, an elegant synergy that enables life to flourish.

It’s a simple message really: everything’s connected. Take out something as important as a big predator in a system, whether a sea lion or a wolf, and the results cascade down from the top predator to the lowest links of the food chain. In turn those effects influence other systems, such as nutrient cycling back to the earth, and sometimes even people, quite directly.

In Africa, the loss of lions has allowed olive baboons to increase. Now farmers are losing crops as the baboons raid their fields. And ultimately, more kids are missing school, because their families are keeping them home to guard the fields.

In the North Atlantic, killing sharks has allowed cow-nosed rays to flourish. That has cratered populations of the bay scallops the rays eat, which in turn has hurt the bay scallop fishing industry.

In a video on his homepage, William J. Ripple, professor in the College of Forestry at Oregon State University, explains how the predator/ecosystem interaction works.

He said the paper is the product of a meeting of scientists from around the world that gathered in Florida a couple of years ago who discovered that as they were all studying their own systems, the presence of a top predator was found to be very important to the functioning of nature and health of the ecosystem.

While each of the scientists had published papers as individual case studies, the scientists synthesized their findings, and in looking at the big picture, realized what they were really seeing is the same dynamic across the globe.

“It’s very much the same lesson for humans, we all walked away with a little more respect and knowledge of the big picture of nature and how it functions, especially with respect to its top predators,” Ripple said.

“The effects are more profound and disruptive than we were thinking in the past, it is quite striking,” he said.

So what to do? For one, become aware of how natural systems work. And, where possible, reintroduce these animals where they can do what they do — and gradually put right the function of natural systems that depend on them.



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