An organism whose decline or removal from a habitat causes many other species numbers to change dramatically is called species.

keystone species

Explanation:

Keystone species are species that are very critical to the balance and existence of an ecosystem. They are important species that play a major role in determining the overall diversity in a particular ecosystem. The presence or the removal of a keystone species from an ecosystem would certainly have an effect on the existence of other species in that particular ecosystem.

For example, the gray wolf in the Yellowstone ecosystem can be regarded as a keystone species, as their removal brought about an avast and drastic change to the ecosystem of the park. The gray wolf's predatory activities is said to be fundamental and important in maintaining the balance of the ecosystem of the park and also maintaining its overall species diversity.

the correct answer is b