# Explain how a keystone species influences the ecological niches available to other species within a community.

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

> The sea otter (Enhydra lutris) feeds heavily on sea urchins in kelp forest ecosystems. In areas where sea otters have been removed, sea urchin populations increase dramatically and overgraze kelp, destroying the kelp forest habitat.

## Mark scheme (4 marks)

1. A keystone species has a disproportionately large effect on community structure relative to its abundance / biomass.
2. By controlling populations of another species (e.g. sea otters controlling sea urchins), the keystone species prevents competitive exclusion / allows a greater diversity of species to occupy niches.
3. The keystone species can create or maintain habitat / structural complexity, thereby generating new or more diverse niches for other species (e.g. sea otters maintaining kelp forests which provide niches for many other organisms).
4. When the keystone species is removed, niche diversity decreases as dominant species expand and outcompete others, reducing the number of realised niches available in the community.

## Key terms

- [keystone species](https://www.gradenine.co.uk/glossary/keystone-species)
- [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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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-a-keystone-species-influences-79abfce9) · Published by Druglandscape Ltd.