The new AQA GCSE topic on ecosystems looks at the impacts of the reintroduction of the grey wolf to the Yellowstone ecosystem.
Read, watch and answer the question!
When Yellowstone National Park was created in 1872, gray wolf (Canis lupus) populations were already in decline in Montana, Wyoming and Idaho. However, the creation of the national park did not provide protection for wolves or other predators. Shortly after Yellowstone’s designation as a national park, the government, prodded by ranchers and farmers recently settled outside the park’s boundaries took the view that wolves were varmints. Their habit of killing prey like elk and deer, both considered “more desirable” species than wolves, and also of sometimes going after livestock was deemed “wanton destruction” of those animals. Government predator control programs in the first decades of the 1900s essentially helped eliminate the gray wolf from Yellowstone. The last wolves were killed in Yellowstone in 1926.
In ecology, there is a phenomenon called top-down trophic cascades—essentially rippling impacts that occur in landscapes when key animals, like wolves, are removed from the top of the food chain. After wolves disappeared from Yellowstone in the 1930s, elk numbers in subsequent decades exploded.
By the late 1980s, half a decade prior to wolf reintroduction, range scientists from Montana State University’s College of Agriculture declared, “There were too many elk.” They said Yellowstone’s grasslands were severely overgrazed and that aspen, willow, and cottonwood trees were imperilled because of foraging wapiti.
After wolves were reintroduced, the elk population tumbled dramatically but not dangerously. Researchers across the ecosystem note that fewer elk are resulting in more aspen, willow, and cottonwoods. And with more willow, there are more beavers, which, in turn, create wetlands that benefit moose and songbirds and other marsh-dependent species. It is hypothesized that rivers will flow healthier. Because wolves also kill coyotes, which prey on pronghorn fawns, conjecture is that antelope numbers will grow. And with fewer coyotes, which are huge consumers of rodents, it is suggested that mouse- and ground-squirrel-eating raptors are more abundant.
Watch the two following videos. Take notes and answer the 9 mark question (+ 3 SPaG marks):
Explain how changes to the ecosystem in turn changed the physical environment of Yellowstone park.
Structure your answer in two sections:
1- Explain the impacts of the disappearance of wolves on the ecosystem.
2- Explain the impacts of their reintroduction.
The importance of predators, the Yellowstone case
How Wolves Change Rivers