Tuesday, September 25, 2012

Top Predator on the Plains: Wolf, Bear or Human?

Looking back in time, who was the top predator of the American prairie ecosystem? Wolves, grizzly bears… humans? As I continue my research of historic wildlife populations in northeastern Montana (read my first post here), it is important to consider how changes in human populations were affecting the ecology of this area. There was a tendency among European and American explorers to romanticize the landscapes they encountered as pristine paradises flourishing with wild animals and vegetation. In fact, this land had been inhabited by hundreds of thousands of humans that had shaped the ecosystem in variable ways.

Aboriginal peoples in the Northern Plains hunted a variety of game animals, but buffalo was certainly the fundamental source of food, clothing, tools and shelter. Archaeological evidence indicates that humans hunted buffalo in Montana as early as 11000 B.C., but it was during the middle prehistoric (4000 to 500 B.C.) that cultures made wide use of buffalo jumps – cliffs over which humans could drive a whole herd of buffalo for slaughter. Archaeologists estimate that humans killed up to 200,000 bison a year in Montana using this method, whereas wolves only killed 25,000.

View from a buffalo jump as it exists today on the Charles M. Russell National Wildlife Refuge, just south of American Prairie Reserve in Montana. Photo by David Driscoll.

Attempting to measure how significantly Native Americans restricted wildlife ranges and constrained population sizes is controversial. Some researchers theorize that aboriginals had a tremendous impact on wildlife and that it is a mistake to view Native American cultures as “conservationist.” (Alvard 1993, Kay 1994). An entry from William Clark’s journal has been used to support this hypothesis. On August 29th 1806, near Chamberlain, South Dakota, Clark comes across a herd of buffalo that he claims must number 20,000 and writes, “I have observed that in the country between the nations which are at war with each other the greatest number of wild animals are to be found.” This observation has prompted academics to consider whether large populations of wildlife were funneled into “buffer zones” between warring tribes where they were safe from human threat (Martin and Szuter 1999, Laliberte and Ripple 2001).

Other experts think that this theory is overstated or completely wrong. These scientists and historians point to huge climatic changes and biogeographic differences that could have accounted for the wildlife distributions observed by Lewis and Clark (Yochim 2001, Lyman and Wolverton 2002). Most notably, from 1500 to 1850, advancing glaciers created something known as the Little Ice Age on the Northern Great Plains. Species like pronghorn, elk, and deer would have been particularly affected by colder temperatures and increased snow depth.

“Hunting of the Grizzly Bear” by Karl Bodmer, 1842. Source: National Museum of Wildlife Art.

I sat down recently with Yellowstone historian Paul Schullery to discuss grizzly bear populations in Montana. Instead, we spent much of our time discussing changes in the prairie landscape over time. “Nothing is stable,” Schullery said. “Things change all the time, and they had already changed because of the horse . . . [Lewis and Clark] were not seeing an unaffected situation.”

Horses allowed man the element of mobility and precision that had never existed previously. Northern Plains tribes like the Blackfoot, Crow, Mandan, and Hidatsa had access to the horse starting in the mid 1700’s. When Lewis and Clark arrived, these tribes were going through a massive cultural shift, and the effect of that transition had not been fully realized.

“Assiniboine hunting buffalo,” painting by Paul Kane circa 1851-1856. Source: Learn NC.

While the horse made the Plains Indians much more effective hunters, small pox was simultaneously devastating their populations. European explorers brought to America a slew of Old World diseases for which Native Americans were immunologically unprepared. Lewis and Clark spent the winter of 1804-1805 at Fort Mandan in western North Dakota, where an estimated 90% of the population had been wiped out in the preceding half century. This extreme effect on a top predator would certainly have influenced the population dynamics of other species in the ecosystem.

Dynamics within human populations such as disease, tribal warfare, and integration of the horse help to both muddle and clarify the historic range and abundance of wildlife..