Question

23 multiple choice 2 points
what distinguishes a keystone species from other species in an ecosystem?
it is always a primary producer
it has a small impact relative to its population size
it always occupies the top trophic level
its removal causes a collapse or major shift in the ecosystem

Explanation:

A keystone species is crucial in an ecosystem. It's not always a primary producer (could be a predator like a sea otter). Having a small impact relative to population size is incorrect as its impact is large. It doesn't always occupy the top trophic level. But its removal causes significant ecosystem changes like collapse or major shift, which is the key characteristic.

Answer:

Its removal causes a collapse or major shift in the ecosystem.