# Explain how the concept of the realised niche differs from the fundamental niche, and outline one factor that can cause a species to occupy a realised niche smaller than its fundamental niche.

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

## Mark scheme (4 marks)

1. The fundamental niche is the full range of abiotic and biotic conditions under which a species could potentially survive and reproduce.
2. The realised niche is the actual range of conditions and resources a species uses/occupies in the presence of biotic interactions such as competition or predation.
3. The realised niche is a subset of / smaller than or equal to the fundamental niche because biotic interactions restrict a species' actual use of conditions/resources.
4. One factor causing the realised niche to be smaller than the fundamental niche, e.g. interspecific competition excludes a species from part of its potential range of resources; or predation restricts the times/places a species can feed; or parasitism reduces the conditions under which the host can survive.

## Key terms

- [fundamental niche](https://www.gradenine.co.uk/glossary/fundamental-niche)
- [realised niche](https://www.gradenine.co.uk/glossary/realised-niche)

## Related

- [Revision notes for IB DP Biology Higher 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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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-concept-of-the-4a0204ab) · Published by Druglandscape Ltd.