AP Environmental Science

Answer: C - Keystone species are species that play an important role and affect other species in an ecosystem.

Key Takeaway: The keystone species in an ecosystem play an important role that affects other species within an ecosystem. An example of this would be sea otters in California. The otters eat urchins, who eat kelp, that provide food for smaller sea animals. If the otter is removed from the equation, the numbers of the other species in the system gets thrown off balance. Basically, the keystone species provide the large structure of a community with an ecosystem. It is important to note some scientists believe that all species play an equal role in an ecosystem; still, the keystone theory is generally favored.