CORVALLIS, Ore. A new analysis of the extinction of woolly mammoths and other large mammals more than 10,000 years ago suggests that they may have fallen victim to the same type of "trophic cascade" of ecosystem disruption that scientists say is being caused today by the global decline of predators such as wolves, cougars, and sharks.
In each case the cascading events were originally begun by human disruption of ecosystems, a new study concludes, but around 15,000 years ago the problem was not the loss of a key predator, but the addition of one human hunters with spears.
In a study published today in the journal BioScience, researchers propose that this mass extinction was caused by newly-arrived humans tipping the balance of power and competing with major predators such as saber-toothed cats. An equilibrium that had survived for thousands of years was disrupted, possibly explaining the loss of two-thirds of North America's large mammals during this period.
"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," said William Ripple, a professor of forest ecosystems and society at Oregon State University, and an expert on the ecosystem alterations that scientists are increasingly finding when predators are added or removed.
"We believe humans indeed may have been a factor, but not as most current theory suggests, simply by hunting animals to extinction," Ripple said. "Rather, 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."
In the late Pleistocene, researchers say, major predators dominated North America in an uneasy stability with a wide range of mammals: mammoths, mastodons, ground sloths, camels, horses, and several species of bison. The new study cites pr
|Contact: William Ripple|
Oregon State University