A Level Biology Practice Exam

What does succession in an ecosystem refer to?

1. The introduction of new species only

2. The gradual replacement of one community by another

3. The seasonal changes in plant life

4. The return of species after a disturbance

The correct answer is: The gradual replacement of one community by another

Succession in an ecosystem refers to the gradual process by which one biological community replaces another over time. This typically occurs in a series of stages, beginning with pioneer species that are well adapted to colonize disturbed or barren environments. As these organisms modify the environment, conditions become favorable for other species to establish themselves, leading to a shift in community composition. This process can be observed in various ecosystems, such as forests following a fire or the colonization of a bare rock surface post-glacial retreat. Each stage of succession increases biodiversity and culminates in a more stable climax community, which can persist until another disturbance occurs. The other choices focus on specific aspects of ecological changes or events that do not capture the full scope of succession. For example, the introduction of new species only does not encompass the idea of community replacement. Seasonal changes in plant life describe temporal variations within an established community rather than shifts from one community to another. Finally, while the return of species after a disturbance relates to ecosystem recovery, it does not specifically communicate the gradual process integral to succession.