# Explain how the competitive exclusion principle relates to the concept of ecological niches.

> IB DP Biology Standard Level (2023 syllabus) — B4.2 Ecological niches · Explain · 4 marks

> Two species of flour beetle, Tribolium castaneum and Tribolium confusum, were cultured together in the same container with identical food and environmental conditions. Over time, one species was always eliminated from the culture.

## Mark scheme (4 marks)

1. The competitive exclusion principle states that two species cannot occupy the same ecological niche indefinitely in the same habitat.
2. When two species have identical (or near-identical) niches, they compete for exactly the same resources.
3. One species will be a more efficient competitor and will have a higher reproductive rate / survival rate, giving it a competitive advantage.
4. The inferior competitor is excluded (locally extinct / population declines to zero), so in nature coexisting species must occupy different niches / have niche differentiation.

## Key terms

- [competitive exclusion principle](https://www.gradenine.co.uk/glossary/competitive-exclusion-principle)
- [ecological niche](https://www.gradenine.co.uk/glossary/ecological-niche)

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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