"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 saber-toothed tiger, the problems may have begun by adding a predator, in this case humans."
The new analysis draws on many other existing studies in making its case.
For instance, other research describes this process with a model in modern times in Alaska. There, the allowance of relatively limited human hunting on moose caused wolves to switch some of their predation to sheep, ultimately resulting in a precipitous decline in populations not only of moose but also wolves and sheep.
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 important 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.
It seems that diverse and abundant carnivores kept herbivore numbers below levels where food becomes limiting. By contrast, the large population of predators such as dire wolves and saber tooth cats caused them to compete intensely for food, as evidenced by heavy tooth wear.
"Heavily worn and fractured teeth are a result of bone consumption, something most carnivores avoid unless prey is difficult to acquire," says Van Valkenburgh.
Trophic cascades initiated by humans are broadly demonstrated, the researchers report. In North America, it may have started with the arrival of the first humans, but continues today with the extirpation of wolv
|Contact: William Ripple|
Oregon State University