Loss of large predators disrupting multiple plant, animal and human ecosystems

July 14, 2011
Loss of large predators disrupting multiple plant, animal and human ecosystems
A wolf in Yellowstone National Park. (Photo courtesy of Yellowstone National Park)

The enormous decline of large, apex predators and "consumers" ranging from wolves to lions, sharks and sea otters may represent the most powerful impacts humans have ever had on Earth's ecosystems, a group of 24 researchers concluded today in a new report in the journal Science.

The decline of such species around the world is much greater than previously understood and now affects many other through what scientists call "trophic cascades," in which the loss of "top down" severely disrupts many other plant and .

Such disruption is sufficiently severe that it now affects everything from to pollution, , wildfire, climate, and spread of disease, the scientists said. It is also a driving force in the sixth mass extinction in Earth history, which the researchers said is now under way.

"We now have that large predators are hugely important in the function of nature, from the deepest oceans to the highest mountains, the tropics to the Arctic," said William Ripple, a professor of forestry at Oregon State University, co-author of the report and an international leader in this field of study as director of OSU's Trophic Cascades Program.

"In a broad view, the collapse of these ecosystems has reached a point where this doesn't just affect wolves or aspen trees, deforestation or soil or water," Ripple said. "These predators and processes ultimately protect humans. This isn't just about them, it's about us."

Historically there has been little appreciation of how large predators affected so many other species, the researchers said, and too often such processes were studied one plant or animal at a time in a small area, failing to appreciate the larger disruption under way.

Based on the new understanding that is emerging, the scientists argued that the burden of proof should now be shifted, to assume that top predators have major effects on ecosystems until proven otherwise.

"We propose that many of the ecological surprises that have confronted society over past centuries – pandemics, population collapses of species we value and eruptions of those we do not, major shifts in ecosystem states, and losses of diverse ecosystem services were caused or facilitated by altered top-down forcing regimes," the scientists wrote.

Pioneering research done in recent years at OSU and cited in this study, for instance, has outlined the effect that the loss of wolves had in Yellowstone National Park. When wolves were removed, elk populations increased and elk behavior also changed, because they were no longer afraid of browsing young aspen trees in places where historically they might have been vulnerable to wolf attack.

Without wolves, the growth of young aspen trees and willow almost ground to a halt, and there were fewer beaver. Plant communities, tree growth and stream ecology all were affected. With the return of wolves, those areas are now returning to health, and in places, aspen and willow are recovering where they had been declining.

The scientists cited many examples in their study, both terrestrial and marine:

  • Reduction of cougar in Utah led to an eruption of deer, loss of vegetation, altered stream channels, and a decline in biodiversity.
  • Industrial whaling in the 20th century likely caused a killer whale diet shift and a dramatic decline of sea lions, seals and .
  • Decimation of sharks resulted in an outbreak of cow-nosed rays and the collapse of bay scallop fisheries.
  • Sea otters enhance kelp abundance by limiting herbivorous sea urchins.
  • The reduction of lions and leopards in Africa led to a population explosion in olive baboons, which bring intestinal parasites to humans who live in close proximity to them.

For too long, the researchers said, large animals have been seen as "riding atop the trophic pyramid" but not really affecting the species and structure below them. That's a fundamental misunderstanding of ecology, they said.

This report was done by scientists from 22 different institutions in six countries. Studies were supported by the Institute for Ocean Conservation Science at Stony Brook University, National Science Foundation, Natural Sciences and Engineering Research Council of Canada, and other organizations.

"Top-down forcing must be included in conceptual overviews if there is to be any real hope for understanding and managing the workings of nature," they wrote in their conclusion.

Explore further: Presence of wolves allows aspen recovery in Yellowstone

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1.7 / 5 (6) Jul 14, 2011
"It is also a driving force in the sixth mass extinction in Earth history, which the researchers said is now under way."

Wow. Nice fabrication. No such thing is happening.

However, the people pushing this lunacy really, really want you to die.

They want us to end agriculture so most of us will starve to death.

"Phase two of the Sixth Extinction began around 10,000 years ago with the invention of agriculture-perhaps first in the Natufian culture of the Middle East. Agriculture appears to have been invented several different times in various different places, and has, in the intervening years, spread around the entire globe."

These are just doom and gloom malthusians.

4 / 5 (4) Jul 14, 2011
"Wow. Nice fabrication. No such thing is happening."

Which is your opinion - not shared by the national academy of sciences - http://www.ncbi.n...2556420/

At this point - whether you understand it or not - science is telling us there is reason to be very concerned about what is happening in the environment. I of course don't care if you wish to put your head in the sand and ignore the warning signs. Sure wish you deniers did not have this religous need to jump on every article published on physorg and spread your nonsense. Just let the science tell us what is - my opinion, and your opinion are insignificant - it is what it is....
4 / 5 (4) Jul 14, 2011
coincidentally - I read an article today showing that lions will go extinct within 15 years if we don't take action. http://www.ncbi.n...2556420/

My vote is that we take the scientists seriously - and see if we can't save the lions, and the tigers. What say you NotParker
Jul 14, 2011
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1 / 5 (4) Jul 15, 2011
You know, there's a reason these apex predators exist -- it's to control prey populations. Removing the apex predators creates an imbalance in the ecosystem. And that's exactly what's happening.
not rated yet Jul 15, 2011
You guys are correct and I thought this effect was well understood and documented. So the whole article is a surprise to me that this is not only news but supposedly a new idea.

Everybody has been talking about jellyfish population increase because of reduced predation for some time. Sure people fish the oceans and eat a lot of stuff but we hardly do so in a balanced way. We just clean up all the edible stuff of a decent size and extract that from the sea without regard to growth rates, habitat, or diet. What is less is either fully grown small fish that used to occupy a limited niche or else juveniles that may never make it to adult hood.
5 / 5 (1) Jul 15, 2011
So what these scientists are saying is that if we start hunting what the apex predators were hunting then we'll prevent all these other bad things from happening. Ultimately the world has always been changing and species have been going extinct since long before the arrival of humans. The "natural" rules of the game are simple; evolve or die. Polar bears are already evolving to the loss of their traditional habitat by breeding with grizzly bears. This natural evolution has already been documented and I'm sure more will follow.

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