The following text is about ecological restoration.
After a century of hunting and habitat destruction, wolves were extirpated from Yellowstone National Park. Their reintroduction in 1995 triggered what ecologists call a "trophic cascade"—changes that rippled through the entire ecosystem. Wolves reduced elk populations, allowing willows and aspens to regenerate. This brought back beavers, whose dams created wetland habitats. Riverbanks stabilized as vegetation returned. Scientists now view the wolf reintroduction as a case study in how predators can restore ecosystem health.
What does the Yellowstone wolf reintroduction demonstrate?
Wolves should be removed from all ecosystems
Top predators can trigger positive changes throughout ecosystems
Elk populations are more important than wolves
Beavers caused the most significant ecosystem changes
Correct Answer: B
Choice B is the correct answer. The text describes how wolves triggered a "trophic cascade" with effects throughout the ecosystem, concluding wolves are a "case study in how predators can restore ecosystem health."
- Evidence: Chain reaction from wolves to elk to plants to beavers to rivers.
- Reasoning: Predators at the top affect the whole system.
- Conclusion: Top predators can restore ecosystem health.
Choice A is incorrect because the text supports wolf presence. Choice C is incorrect because elk reduction was beneficial. Choice D is incorrect because beavers returned due to wolf-caused vegetation.