Leave it to Beavers

Watch, Leave it to Beavers and respond to the following prompts:

1. Why are beavers important to an ecosystem?
2. How would an ecosystem with beavers be different if the beavers were gone?
3. Why are beavers important to humans?
4. A keystone species is a species whose presence and role within an ecosystem has a disproportionate effect on other organisms within the ecosystem.  Why are beavers a keystone species?