Biology Regents Practice Exam

Which event would most severely disrupt the process of ecological succession in an area?

1. The season changes from spring into summer.

2. Native plants are planted in an abandoned field.

3. Plants and animals begin to colonize a newly formed volcanic island.

4. A dam is built on a river to form a reservoir.

The correct answer is: A dam is built on a river to form a reservoir.

The construction of a dam to form a reservoir represents a significant alteration to both the physical environment and the ecological dynamics of an area, thus severely disrupting the process of ecological succession. When a dam is built, it can inundate existing habitats, flooding areas that may have previously supported diverse plant and animal communities. This flooding can lead to the loss of established ecosystems and the organisms that inhabit them. In addition, the formation of a reservoir changes water flow patterns, sediment deposition, and nutrient availability. These changes can radically transform the area, favoring different species that thrive in the new aquatic or semi-aquatic conditions. Consequently, the entire successional trajectory is altered since the original plant and animal communities are displaced, and the area must undergo succession anew under the modified environmental conditions. The other options represent events that generally do not result in such a drastic disruption. Seasonal changes are natural occurrences that ecosystems adapt to. Planting native species can actually aid in the recovery of an abandoned field and enhance its ecological succession. The colonization of a new volcanic island typically reflects the beginning stages of succession, showcasing natural processes rather than disruptions.