Keystone species are:

A. Species that dominate the ecosystem A.

B. Species with minimum ecological importance B.

C. Species whose removal affects the entire ecosystem C.

D. Exotic invasive species D.

A keystone species is a species that has a disproportionately large effect on its natural environment relative to its abundance.

Significant Impact: These species are crucial in maintaining the structure, function, and biodiversity of the ecosystem.
Ecosystem Engineering: Their activities often create or maintain specific habitats or profoundly influence the populations of many other species.
Consequences of Removal: When a keystone species is removed, the entire ecosystem often changes dramatically, sometimes leading to the extinction of numerous other species that depend on it (a phenomenon known as a trophic cascade).

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