superpredators and megafauna in north america -- 10/28/20
Today's selection -- from Wyoming: A History of the American West by Sam Lightner Jr. American lions and saber-toothed cats once roamed North America, along with giant bison, mammoths, beavers and sloths. Then came the Clovis people, considered to be the ancestors of most of the indigenous cultures of the Americas:
"Clovis people … were a new type of predator in North America, [and] the indigenous animals hadn't developed a defense for their hunting techniques. But it was not just hunting that made this a stressful time for the megafauna of North America. Not only was there a new predator that used his brain and tools more than teeth or claws, but the environment the animals were adapted to was quickly changing. It was the end of the last major ice age; the climate was getting warmer. What would have been considered heat waves at the time, entire months without a day below freezing, were becoming more common. Streams were carrying more water, and in some cases, overflowing their banks and creating giant lakes. The Great Lakes are examples of this that are still with us. Ocean levels were also rising, cutting off the migration of animals across Beringia. The change in temperature and precipitation patterns meant changes in the flora those animals lived on. In short, the megafauna of the ice age had to adapt in many ways, and many of these species were not able to do so.
"By studying modern elephants, a very close relative to the mammoth, biologists have identified specific problems for the mammoths and they're associated with the hunting of the giant pachyderms. Columbian mammoths lived a long time, but a female only produced a few young in her life. As each animal needed hundreds of pounds of food per day, mammoths tended to roam in fairly small, isolated herds. A hunting party could wipe out an entire herd in a kill site like Colby. Even if not all of the animals in a given herd were killed, a loss of a few more than the herd was adapted to handle could have devastating consequences. By killing just a few members of the herd every year, a so-called 'genomic meltdown' is set in motion. Each surviving animal has fewer mating choices and is forced into inbreeding. The immune system of their offspring is often compromised, leaving weak animals vulnerable to disease. It has been estimated that if hunters killed just 3 percent of the mammoth population each year, the entire North American herd would have been extinct in a couple centuries.
|Mammuthus primigenius "Hebior Mammoth specimen" bearing tool/butcher marks, cast skeleton produced and distributed by Triebold Paleontology Incorporated|
"Of course this new predator was hunting more than just mammoths, and those other species would have needed to adapt or go extinct as well. Giant ground sloths and cumbersome bison would have been easy prey for Clovis people when they couldn't find a mammoth. Horses, who had been migrating back and forth between Asia and North America, were elusive but still made it onto the Clovis' menu. Short-faced bears and dire wolves no longer had herds of mammoths as a choice of prey, so they focused on giant beavers and bison antiquus. It was an adapt-or-die-out time, with predators pushing dozens of species to extinction. Around ten thousand years ago, the last of the North American horses died. The giant bison soon followed, as did the beaver, sloth, and numerous other species.
"As the numbers of prey animals died off, the predators who had adapted to hunting those animals found it harder to get enough food. Soon the American lion and sabertoothed cat were starved into extinction. Smaller wolves and smaller bears needed fewer calories than dire wolves and short-faced bears, and thus were at an advantage. The camel went extinct in the New World, leaving the smaller alpaca and llama as descendants. Small bison, perhaps more adept at running from atlatl-using humans, managed to survive, as did the pronghorn, but the North American cheetah did not. Most scientists now believe that the introduction of one super predator had brought about an entirely new ecosystem of smaller animals to North America."