A keystone is the center piece of an archway. It’s trapezoidal shape allows the whole frame to stand and keeps both sides balanced. A keystone species provides habitat or food for many other species. It allows a complex community to exist. If the keystone species is removed the ecosystem will collapse, just like taking the “keystone” out of an archway. Beavers are considered a keystone species because their dams create a kind of ‘neighborhood’ for other wildlife.