2nd Intermediate - How wolves changed a river

A trophic cascade is an ecological phenomenon which starts at the top of the food chain and spreads to the bottom.

Watch the following video about how some wolves changed a river and answer the comprehension questions.

1. When were wolves reintroduced? In 1995
2. How long have the wolves been absent? For 70 years
3. How did the deer react when the wolves were reintroduced? They changed their behaviour avoiding some places which began to regenerate
4. What happened to some trees? Their height tripled
5. Which animals appeared when more trees had grown? The birds started moving in
6. Name three types of animals that live in the dams built by beavers: ducks, fish, reptiles, amphibians
7. Why did the number of rabbits and mice rise? Because the wolves killed coyotes
8. Name one of the reasons why the population of bears rose: there were more berries
9. Why did rivers have more fixed courses? Because of the regeneration of the forests

Answers written in white; select the text above to see them.