The Ten Principles of Ecological Restoration...
Pay particular attention to “keystone”
In conservation biology, a keystone specie is one
that plays a central, often critical role in ecosystems, and upon which
many other species depend. If an ecosystem can be returned to a state
in which a keystone specie flourishes, it will have a beneficial cascading
impact on all other species that depend on it. The beaver is a prime
example of a mammalian keystone species. This concept can also apply
to entire habitats, such as vernal pools.