What is a trophic cascade?

• A. A bottom-up effect where resource availability controls producers.
• B. A top-down effect where a predator alters populations at lower trophic levels.
• C. A process of nutrient cycling in detrital chain.
• D. Random population fluctuations due to weather.

Answer: (B)

A trophic cascade is a chain of indirect effects that starts with changes at a higher trophic level, such as a predator, and propagates downward to influence the abundance and interactions of species at lower levels. In a top-down cascade, predators suppress or alter the behavior of prey, which reduces grazing pressure on primary producers and can lead to increases in vegetation and shifts across the entire food web. A classic example is wolves reducing elk numbers and changing how elk feed, allowing forests to recover and supporting a wider array of species that depend on those plants. This contrasts with bottom-up scenarios where resources limit producers and effects move upward, or with processes like nutrient cycling in detrital chains or random weather-driven fluctuations.