Yellowstone Trophic Cascade (Wolf Reintroduction)
Trophic Cascade – Defined as occurring when predators in a food web
suppress the abundance or alter the behavior of their prey, thereby
releasing the next lower trophic level from predation.
 Wolves reintroduced in Yellowstone in 1995 in the Lamar Valley.
 Since wolves were reintroduced the elk and deer are stronger,
the aspens and willows are healthier and the grasses taller.
 When wolves hunt elk, the elk have to run faster and farther,
causing their hooves to aerate the soil, allowing more grasses to
grow.
 With the presence of wolves, elk are much less stationary than
before. They also tend to avoid the wide open valleys and stay
more on the fringes of the forests. This keeps them from
overgrazing the aspen and willow shoots and allows them to
fully recover between elk migrations.
 Within 6 years, some of the trees in the areas frequented by elk
prior to the wolf reintroduction, but now largely avoided by elk,
saw their height quintuple.
 Once the aspen, willows, and cottonwoods retook the forest
floors, birds started to return.
 With more trees, the beaver population increased. There was
one documented beaver colony in Yellowstone in 2001. By 2011,
there were 9.
 The dams the beavers built provided habitat for muskrats,
ducks, otters, fish.
 In areas occupied by wolves in Yellowstone, the coyote
population has been reduced in some cases by as much as 80%.
 With fewer coyotes hunting the small rodents, raptors such as
eagles and osprey have made a comeback.
 Grizzlies successfully steal wolf kills more often than not,
providing more food for their cubs, thus making them healthier
and more likely to survive.
 With more regenerating shrubs, there were also more berries for
the bears to eat.
 With banks stabilized by the regenerating flora, the rivers began
to meander less. The banks of the rivers collapsed less often and
were much less susceptible to erosion.
 With the deer and elk much less prominent in the valleys, there
was less soil erosion as the sides of the valleys stabilized.
 All of this came from the reintroduction of wolves in 1995.
Amazing.