Succession occurs because a. organisms gradually change the environment b. climax communities are not possible c. dominant organisms drive out pioneer species d. ecosystems never reach a sustainable point.

Succession occurs because dominant organisms drive out pioneer pecies Succession basically implies that every ecosystem gradually changes and develops with time.Due to changes in the environment, pioneer species become less capable of adapting to the new environment. As such, these species are not able to compete with other organisms because the new organisms are able to thrive in the new conditions.