Explain how a keystone species contributes to the stability of an ecosystem.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
A keystone species has a disproportionately large effect on ecosystem structure relative to its biomass or abundance.
Removal or decline of the keystone species causes significant loss of biodiversity or collapse of community structure.
Keystone species regulate populations of other species, for example by predation or herbivory, preventing any one species from dominating.
By maintaining species diversity, the keystone species sustains multiple trophic levels and ecological interactions such as mutualism, pollination and habitat provision, thereby conferring overall ecosystem resilience.
Removal or decline of the keystone species causes significant loss of biodiversity or collapse of community structure.
Keystone species regulate populations of other species, for example by predation or herbivory, preventing any one species from dominating.
By maintaining species diversity, the keystone species sustains multiple trophic levels and ecological interactions such as mutualism, pollination and habitat provision, thereby conferring overall ecosystem resilience.
Examiner tips
- Use the word ‘keystone species’ and explain its disproportionate influence. Show the cause–effect chain: removal → loss of biodiversity → collapse of structure. Mention regulation of other species and the maintenance of multiple trophic levels. Keep the answer concise and use the exact terminology from the mark scheme.
Common mistakes
- Confusing a keystone species with a keystone predator or general predator. Failing to mention the effect on biodiversity or community structure. Using vague phrases like ‘important species’ without showing disproportionate influence.
Mark scheme (4 marks)
- A keystone species has a disproportionately large effect on ecosystem structure relative to its biomass/abundance.
- Removal or decline of the keystone species causes significant loss of biodiversity / collapse of community structure.
- Keystone species regulate populations of other species (e.g. by predation or herbivory), preventing any one species from dominating.
- 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 in this question
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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