State the competitive exclusion principle and its implication for similar mammals.

• A. No two species can occupy the same niche indefinitely.
• B. Two species can share identical niches indefinitely if they are different sizes.
• C. Competition always leads to extinction of one species immediately.
• D. No two species can occupy the same niche indefinitely; they must partition resources or diverge.

Answer: (D)

The main idea is that when two similar mammals rely on the same limited resources, they can’t coexist in exactly the same way forever. The competitive exclusion principle states that identical niches can’t be maintained indefinitely in the face of competition. To share a space over the long term, the species must split up how they use resources or evolve differences that reduce overlap.

That’s why the best answer emphasizes both the limit on indefinite overlap and the outcome: species must partition resources or diverge. In practice, similar mammals might feed on different parts of the same plant, hunt at different times, use different microhabitats, or develop distinct foraging techniques. These adjustments lessen direct competition and allow coexistence.

If two similar species tried to occupy the exact same niche without any differences, one would be outcompeted in the long run.