Listen to part of a lecture in an environmental science class. Professor: Today we're going to discuss a fascinating example of ecological restoration. Let's talk about the reintroduction of gray wolves to Yellowstone National Park in 1995. Before wolves were removed in the 1920s, elk populations had been kept in check. But without their natural predator, elk numbers soared, and they overgrazed young willow and aspen trees along rivers. This caused erosion and a decline in beaver populations, because beavers depend on those trees for food and dam building. When wolves were brought back, they not only reduced elk numbers but also changed elk behavior. Elk started avoiding open river areas, which allowed vegetation to recover. With more trees, beavers returned, and their dams created habitats for fish and birds. This cascade effect shows how top predators can shape entire ecosystems. So, the wolves didn't just affect elk—they transformed the landscape itself.
❓ Pregunta What is the main point the professor makes about the reintroduction of wolves to Yellowstone?
A. Wolves directly caused a decline in beaver populations.
B. Wolves indirectly restored the ecosystem by affecting elk behavior and vegetation.
C. Wolves were removed because they overgrazed willow trees.
D. Wolves had no impact on the river systems in Yellowstone.
✅ Respuesta correcta
Wolves indirectly restored the ecosystem by affecting elk behavior and vegetation.
TOEFL Listening Tips
Skim the questions first to predict the content
Watch for signal words in lectures and conversations (however, actually, in fact)
For main idea questions, focus on the beginning; for detail questions, focus on examples and data
For attitude questions, pay attention to the speaker's tone and word choice
Take notes on keywords; don't try to write down every word