What Do Woolly Mammoths and Whales Have in Common?


Image credit: Wikimedia Commons

15,000 years ago the ecosystems of North America suffered a dramatic disruption. Within 5,000 years, dozens of Pleistocene species—including herbivores like mammoths, mastodons, ground sloths, and camels, and predators like lions, dire wolves, and two species of saber-toothed cats—went extinct. In all, two-thirds of the continent's large mammals were lost during this period.

And the disruption has direct analogs to shifts occurring in North America today.William Ripple, a professor of forest ecosystems and society at Oregon State University, explained:

For decades, scientists have been debating the causes of this mass extinction, and the two theories with the most support are hunting pressures from the arrival of humans, and climate change.

His new study, which draws on decades of related research, concludes that, in fact, the Pleistocene extinctions were the result of the addition of a new predator to the ecosystem: humans.

He commented:

We think humans provided competition for other predators that still did the bulk of the killing. But we were the triggering mechanism that disrupted the ecosystem.

The process, his research indicated, was much more complicated than simply hunting megafauna to extinction.


Image credit: Wikimedia Commons

Instead, he suggests, human activity disrupted a delicately balanced system by increasing competition between predators and at the same time reducing the range of herbivores. Increasingly stressed predators hunted their primary prey to extinction.

WATCH VIDEO: Land of the Mammoth: Extinction Theories

The process, called a "trophic cascade," is not limited to the distant past. Today, the catalyst is typically caused by the elimination of a key predator or herbivore. One example is the extirpation of wolves in Yellowstone. Once this predator was removed, the caribou population exploded, leading to damage aspen forests and impacts on everything from fish to birds, trees to beaver.

In the oceans, the depletion of whale populations is believed to be responsible for shifts in orca predation, dramatic declines in sea lion and sea otter populations, ballooning numbers of urchins, and the collapse of kelp forests.

From the ocean to Yellowstone, the Pleistocene to today, all of these examples have one thing in common: human activity.

"This is a sobering thought," Ripple writes in his report, "but it is not too late to alter our course this time around in the interest of sustaining Earth's ecosystems."

Read more about ecosystems:
Wolves Can Help Restore Ecosystems
Good News: Most Ecosystems Can Recover in One Lifetime from Human-Induced or Natural Disturbance
Life on the Endangered Species Waiting List

Tags: Conservation | Endangered Species

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