# Explain how keystone species influence the structure of an ecological community, including the effect of their removal on species diversity.

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

## Mark scheme (4 marks)

1. A keystone species has a disproportionately large effect on community structure relative to its abundance or biomass.
2. Keystone species regulate populations of other species (e.g. prey or competitors), thereby maintaining niche diversity and preventing competitive exclusion.
3. Removal of the keystone species leads to dominance by one or a few species, reducing species diversity (trophic cascade / diversity collapse).
4. The keystone species therefore defines the range of realised niches available to other species in the community; its presence maintains niche heterogeneity.

## Key terms

- [keystone species](https://www.gradenine.co.uk/glossary/keystone-species)
- [species diversity](https://www.gradenine.co.uk/glossary/species-diversity)

## 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-keystone-species-influence-the-c63d83d6) · Published by Druglandscape Ltd.