# Explain how a keystone species contributes to the stability of an ecosystem.

> IB DP Biology Standard Level (2023 syllabus) — D4.2 Stability and change · Explain · 4 marks

## Mark scheme (4 marks)

1. A keystone species has a disproportionately large effect on ecosystem structure relative to its biomass/abundance.
2. Removal or decline of the keystone species causes significant loss of biodiversity / collapse of community structure.
3. Keystone species regulate populations of other species (e.g. by predation or herbivory), preventing any one species from dominating.
4. By maintaining species diversity, the keystone species sustains multiple trophic levels and ecological interactions (e.g. mutualism, pollination, habitat provision), conferring overall ecosystem resilience.

## Key terms

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

## 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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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-a-keystone-species-contributes-84df78b1) · Published by Druglandscape Ltd.