Biology

The correct answer is: A.They are always the most numerous species.

This is NOT a characteristic of keystone species. Keystone species are defined by the large effect they have on their ecosystem relative to their abundance, but they are not necessarily the most numerous species in that ecosystem. In fact, many keystone species are relatively few in number but still play a critical role in shaping the ecosystem.

Here's why the other options are correct:

B.They have a large effect on their ecosystem: This is true. Keystone species have a disproportionately large impact on the structure, function, and stability of their ecosystem. Their removal or decline often causes signifi...