Which of the following statements correctly describes the full value of a keystone species on its ecological community?

A. They are non-native organisms that can damage the ecosystem, so removing them increases biodiversity.

B. They are the largest species in a community and consume more than the others, keeping other populations in check.

C. They are superior predators that displace inferior competitors.

D. They have a disproportionate effect relative to their frequency in the population, so the ecosystem often collapses when they are removed.