# Explain how two species occupying the same habitat can coexist without competitive exclusion occurring.

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

> Two warbler species, species A and species B, live in the same coniferous forest. Species A forages predominantly at the tips of upper branches, whilst species B forages mainly in the lower interior branches of the same trees.

## Mark scheme (4 marks)

1. Each species occupies a distinct ecological niche, so direct competition for identical resources is avoided
2. Resource partitioning means the two species use different parts of the resource (e.g. foraging at different heights / zones in the tree), reducing overlap in food or space
3. The competitive exclusion principle states that two species cannot indefinitely occupy exactly the same niche; niche differentiation allows stable coexistence by preventing one species from outcompeting the other
4. Niche differentiation can involve any combination of abiotic or biotic factors such as food type, feeding time, microhabitat use, or predator avoidance behaviour, allowing populations of both species to be maintained

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