Which process refers to the gradual changes in species composition after a disturbance?

• A. Succession
• B. Biodiversity
• C. Pioneer species
• D. Keystone species

Answer: (A)

Succession is the gradual change in which the species composition of a community shifts over time after a disturbance. When an event like a fire, flood, or logging alters an ecosystem, the environment becomes suitable for different organisms to move in and create a new community step by step. Early on, pioneer species that tolerate harsh, open conditions colonize, slowly modifying the environment—doing things like stabilizing soil and adding organic matter—so that more species can establish. Over time, the community becomes more diverse and structured, moving through successive stages until it reaches a relatively stable configuration.

Biodiversity is the measure of how many and how varied the species are, not the process itself. Pioneer species refer to the first organisms that arrive, not the overall gradual change. Keystone species are those with a disproportionately large effect on the ecosystem’s structure and function. Because the question describes the progressive replacement of species after disturbance, succession is the best fit.