The Yellowstone Trophic Cascade and the Role of Wolves in Ecosystem Balance

In the early 90s, Yellowstone had only one beaver colony, but now there are over nine, thanks to the reintroduction of grey wolves. Wolves, once extinct in the park, were reintroduced in the mid-90s, leading to a trophic cascade that restored ecological balance. Without wolves, elk populations soared, decimating vegetation and affecting other species. The return of wolves reduced elk numbers and changed their behavior, allowing vegetation to recover. This recovery supported beaver recolonization, which further enhanced the ecosystem. The presence of wolves also benefited other predators and scavengers, demonstrating the critical role of apex predators in maintaining ecological balance.

What surprising species led to the discovery of the trophic cascade in Yellowstone?

• Mountain Lion

• Bald Eagle

• Grey Wolf

• Grizzly Bear

What was the primary consequence of the absence of wolves in Yellowstone?

• Explosion in elk numbers

• Decline in elk population

• Increase in tree cover

• Increase in beaver population

How did the reintroduction of wolves affect elk behavior?

• Elk numbers increased

• Elk stayed in one place

• Elk became more aggressive

• Elk had to keep moving

What was the effect of elk movement on vegetation?

• Vegetation continued to decline

• Vegetation began to recover

• Vegetation was unaffected

• Vegetation remained unchanged

How did the recovery of willow stands affect beavers?

• Beavers stopped building dams

• Beavers' numbers declined

• Beavers recolonized the rivers

• Beavers left the area

What role did beavers play in the ecosystem after their return?

• They caused river erosion

• They built dams that stored water

• They reduced fish populations

• They increased coyote numbers

How did the presence of wolves benefit other predators?

• Provided more carrion

• Decreased predator numbers

• Increased competition for food

• Reduced food sources

What was the impact of wolves on coyote populations?

• Coyotes increased in number

• Coyotes were unaffected

• Coyotes became apex predators

• Coyotes were reduced

What is a trophic cascade?

• An increase in herbivore populations

• A decline in plant species

• A chain reaction affecting the entire ecosystem

• A process where apex predators are removed

What is the overall lesson from the Yellowstone wolf reintroduction?

• Predators are harmful to ecosystems

• Ecosystems thrive without predators

• Herbivores control ecosystem health

• Keystone predators are crucial for balance