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 previous evidence from carnivore tooth wear and fracture, growth rates of prey, and other factors that suggest that there were no serious shortages of food caused by environmental change 10,000 to 15,000 years ago.
The large herbivores seemed to be growing quickly, and just as quickly had their numbers reduced by a range of significant carnivorous predators, including lions, dire wolves and two species of sabertooth cats. Food was plentiful for herbivores, and the system was balanced, but it was dominated by predators.
Humans were the triggering mechanism for the extinction. 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.
"We think the evidence shows that major ecosystem disruptions, resulting in these domino effects, can be caused either by subtracting or adding a major predator," Ripple said. "In the case of the woolly mammoths and sabertooth tiger, the problems may have begun by adding a predator, in this case humans."
The loss of species in North America during the late Pleistocene was remarkable; about 80 percent of 51 large herbivore species went extinct, along with more than 60 percent of large carnivores. Previous research has documented the growth rates of North American mammoths by studying their tusks, revealing no evidence of reduced growth caused by inadequate food, thus offering no support for climate-induced habitat decline.
|Contact: Stuart Wolpert|
University of California - Los Angeles