Question

In an Arctic Ocean food chain, killer whales feed on sea otters, which feed on sea urchins, which in turn feed on kelp (a type of seaweed). An increase in the abundance of killer whales causes sea otter abundance to decline, leading to higher sea urchin densities, which in turn reduces the abundance of kelp. Which of the following terms describes this phenomenon?

• A. Trophic cascade
• B. Prey switching
• C. Competitive exclusion
• D. Productivity-stability relationship

Hint:

Trophic cascades demonstrate the top-down effects of predator-prey interactions through the food web.

Answer 1

The Correct Option is A

A trophic cascade occurs when changes at the top of the food chain influence multiple lower trophic levels.

Step 1: Define trophic cascade.
In this example, killer whales (top predator) affect the abundance of sea otters (secondary predator), which indirectly increases sea urchin populations. The resulting increase in sea urchins negatively impacts kelp (primary producer). This is a typical example of a trophic cascade, where one top-down effect propagates through the food chain.

Step 2: Consider other options.
- Prey switching: Refers to a predator changing its prey preference; this is not applicable here.
- Competitive exclusion: Describes a situation where one species outcompetes another, leading to the latter's local extinction. Not applicable in this context.
- Productivity-stability relationship: Refers to the effect of productivity on the stability of an ecosystem, not the chain of trophic interactions described here.

Step 3: Conclusion.
The correct term for this phenomenon is a trophic cascade.