What is a likely outcome if a keystone species is removed from an ecosystem?

• A. Biodiversity increases dramatically.
• B. Cascading changes across structure and function occur.
• C. The ecosystem becomes a closed system.
• D. The trophic level increases only.

Answer: (B)

Removing a keystone species shows how one species has a disproportionately large impact on the whole system. Its role helps regulate populations, interactions, and processes that keep the ecosystem balanced. When that species is removed, the relationships among other organisms shift, and effects ripple through feeding networks, habitats, and nutrient cycling. These cascading changes can alter which species persist, how much vegetation or habitat is available, and how energy and matter move through the community. That’s why the outcome is described as cascading changes across structure and function.

The other ideas don’t fit. Biodiversity doesn’t typically rise dramatically when a keystone species is removed; it often drops as chains of interactions unravel. An ecosystem isn’t a closed system just because a keystone species is gone—the system remains open to energy and matter exchange. And removing a keystone species affects more than a single trophic level; it disrupts multiple levels and interactions, not just one.