What is the role of the beaver in its ecosystem?

 It is a keystone species that modifies its natural environment by damming streams to form wetlands.

Explanation:

A keystone species is an organism which helps in the development of the entire ecosystem. A keystone species makes the environment of the ecosystem suitable for the survival of other species. The keystone species can act as a prey or predator.

The beavers create wetlands and build dams upon which many species depends. The majority of the endangered species in North America rely on the wetland created by the beavers for their survival. This way beavers modify the natural environment of the region.