Question

A species whose impact on an ecosystem is disproportionately large in comparison to its population is called ______ species.

• A. dominant
• B. keystone
• C. apex predator
• D. endemic

Hint:

Think of a species with a small population but outsized control over ecosystem structure, like a keystone holding up an arch.

Answer 1

The Correct Option is B

This question tests a core ecological concept describing species whose ecological importance is much greater than their numerical or biomass abundance would suggest.
Step 1: Recall the definition being described. The question describes a species whose impact on its ecosystem is disproportionately large compared to its population size or abundance.
Step 2: Match this definition to the correct ecological term. This is precisely the textbook definition of a keystone species. A classic example is the sea otter, which controls sea urchin populations and thereby preserves kelp forests, even though otters themselves may be relatively few in number.
Step 3: Rule out the other terms. A dominant species is one that is abundant and has high biomass, meaning its influence comes from its large numbers, not a disproportionate impact relative to low abundance. An apex predator is simply a species at the top of the food chain with no natural predators of its own, which is a different concept from disproportionate ecological impact. An endemic species is one restricted to a specific geographic area, which describes distribution, not ecological influence.
Step 4: Conclude. Since the defining feature in the question is a large ecological effect relative to a small population, the correct term is keystone species, option (B).