Which scenario illustrates a trophic cascade?

• A. Predators have no effect on other species.
• B. Removing a top predator increases herbivore populations and reduces vegetation.
• C. A predator reduces prey numbers without affecting other species.
• D. Prey populations always decline in the absence of predators.

Answer: (B)

A trophic cascade is a chain of indirect effects that starts when a change at one trophic level—often the removal or addition of a top predator—causes shifts in herbivore populations, which then ripple down to affect vegetation or other lower levels. In this scenario, removing a top predator lifts the pressure on herbivores, allowing their numbers to rise. The larger herbivore population grazes more, reducing vegetation. That cascade—from predator to herbivores to plants—illustrates the classic top-down control that characterizes trophic cascades.

The other possibilities don’t show this indirect, multi-step impact. If predators have no effect on other species, there’s no cascade. If a predator reduces prey numbers but doesn’t influence other species, the effect stays limited and doesn’t propagate through the ecosystem. If prey typically decline without predators, that contradicts common cascade dynamics and ignores the potential for vegetation and other species to respond.