Which of the following best defines ecological succession?

Ecological succession is best defined as the gradual change in species composition of a community over time. This process typically occurs in a series of stages, where one group of species gradually replaces another. Succession can be initiated by disturbances such as fires, storms, or human activities, and it leads to changes in environmental conditions, habitats, and available resources.

Primary succession occurs in lifeless areas where soil has yet to form, while secondary succession occurs in areas where disturbance has destroyed a community but leaves the soil intact. In both cases, the succession process can take many years and often results in a stable climax community dominated by a certain type of vegetation or species.

This definition emphasizes the dynamic nature of ecosystems and how they evolve over time, adapting through various phases until a stable community is established. Other options do not accurately depict this process; for example, extinction and immediate impacts from disasters are temporary phenomena, and the introduction of new species does not necessarily imply a gradual change in an existing community's composition.