Thirty-one gray wolves from Canada were turned loose in Yellowstone in the 1990s.
The iconic canines were soon tearing after elk in the U.S. national park, which had not seen wolves in seven decades.
Aspen,
willow and cottonwood trees have begun to sprout now that the elk are
in check. Beavers have started to move back in, increasing habitat for
birds and insects.
"It's amazing the effect one species,
the wolf, can have on the entire ecosystem," says William Ripple, at
Oregon State University, co-author of an international report on the
profound and cascading impact large animals have on ecosystems.
He
and his colleagues say the demise of lions, wolves, bison, sharks,
great whales and other large animals is part of the "the sixth mass
extinction" now underway, and that their disappearance affects
everything from wildfires to the spread of disease.
"The
loss of these animals may be humankind's most pervasive influence on
nature," the team of 24 scientists from the United States, Europe,
Africa and Canada are reporting Friday in the journal Science.
So-called
"apex consumers" have roamed the planet for millions of years but have
vanished from most of their range, largely because of human hunting and
fishing, and habitat loss.
The scientists point to "extensive cascading effects."
"The
disappearance of these animals reverberates further than previously
anticipated, with far-reaching effects on processes as diverse as the
dynamics of disease; fire; carbon sequestration; invasive species; and
biogeochemical exchanges among Earth's soil, water and atmosphere," they
say.
They also suggest the loss of the top animals can be
linked to "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."
The report lists examples from Africa to the Aleutian Islands.
The
reduction of lions and leopards in the sub-Sahara caused the baboon
population to swell. This unexpectedly increased transmission of
intestinal parasites from baboons to humans as the primates foraged
closer to human settlements.
Industrial whaling in the 20th
century killed off large numbers of plankton-eating great whales, which
sequester carbon into the deep sea in their feces. The scientists say
about 105 million tonnes of carbon has ended up in the atmosphere,
contributing to climate change, instead of resting at the bottom of the
ocean.
Coastal kelp forests, important marine nurseries and
habitat, were decimated when sea otter populations collapsed from
over-hunting in the Pacific Northwest. This was because kelp-grazing sea
urchins proliferated when sea otters were no longer around to eat them.
The
loss of sharks has lead a boom in the population of cow-nosed rays,
which have in turn triggered collapse of shellfish populations along the
East Coast of North America.
The researchers, including
zoologist Anthony Sinclair at the University of B.C., who could not be
reached for comment, say that large animals have long been seen as
"riding atop" ecosystems but not really affecting the species and
structure below.
That, they say, is a fundamental misunderstanding of ecology.
"By
looking at ecosystems primarily from the bottom up, scientists and
resource managers have been focusing on only half of a very complex
equation," lead author James Estes, at the University of California at
Santa Cruz, said in a summary of the findings.
The wolves in Yellowstone show the damage is not necessarily irreversible, Ripple told Postmedia News.
He
and associates have been documenting the "restoration" that started in
the park's ecosystem after 31 grey wolves from Alberta were introduced
in Yellowstone the 1995 and 1996, and the packs began to grow.
The
wolf, once widespread across most of North America, has been hunted
ruthlessly and was eradicated from Yellowstone by the 1920s. During the
wolves' seven-decade absence from the park, Ripple says, elk not only
increased in number but their behaviour changed.
The elk
were no longer afraid of browsing young aspen trees in places where
historically the animals might have been vulnerable to wolf attack. As a
result, the growth of young aspen trees and willow almost stopped, and
there were fewer beaver. Plant communities, tree growth and stream
ecology all were affected, Ripple said.
But in parts of
Yellowstone, he said, aspen and willow are now recovering. The trees and
shrubs are attracting more beavers, which in turn set the stage for
more birds and insects.
"It is shocking and very humbling
to see how an individual species can be so important," he said of the
wolves' cascading effect on the ecosystem.
Habitat-restoration
efforts often start from the ground up, with the planting of trees or
other landscape manipulations, said Ripple, "but here all we had to do
was release a few dozen wolves and let them do their thing."
mmunro(at)postmedia.com
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TAhe
Rajiv Gandhi Zoological Park, popularly known as Katraj Zoo, will soon
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everything goes as planned. 
By Xinle Ng