Quite contrary to that, the large herbivores seemed to be growing quickly and just as quickly had their numbers reduced by a range of significant carnivorous predators, not the least of which was lions, dire wolves, and two species of saber-toothed cats. Food was plentiful for herbivores, the system was balanced, but it was dominated by predators.
"When human hunters arrived on the scene, they provided new competition with these carnivores for the same prey," said Blaire Van Valkenburgh, an expert at UCLA on the paleobiology of carnivores, and a co-author with Ripple on this study.
"The humans were also omnivores, and could live on plant foods if necessary," Van Valkenburgh said. "We think this may have triggered a sequential collapse not only in the large herbivores but ultimately their predators as well. Importantly, humans had some other defenses against predation, such as fire, weapons and living in groups, so they were able to survive."
But the driving force in eliminating the large mammals, according to the new theory, was not humans they just got the process started. After that, predators increasingly desperate for food may have driven their prey to extinction over long periods of time and then eventually died out themselves.
In recent studies in Yellowstone National Park and elsewhere, scientists from OSU and other institutions have explored these "trophic cascades," often caused by the loss or introduction of a single major predator in an ecosystem. With the elimination of wolves from Yellowstone, for instance, the numbers of elk exploded. This caused widespread overgrazing; damage to stream ecosystems; the slow demise of aspen forests; and ultimate effects on everything from trees to beaver, fish, bir
|Contact: William Ripple|
Oregon State University