Explain why maintaining high biodiversity within a community is important for the long-term stability of that community.

AQA A-Level Biology (7402) — 3.4.6 Biodiversity Within a Community · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (5 marks)

1. A community with many species has a greater variety of organisms.
2. The food web is more complex, giving more feeding links between species.
3. If one species disappears, other species can replace its ecological role.
4. This replacement reduces the chance that other species will also go extinct.
5. Low biodiversity makes a community more vulnerable to disease, environmental change and the loss of a key species, which can collapse the whole system.

Examiner tips

Use the exact wording from the mark scheme (e.g., ‘greater variety of species’, ‘more feeding relationships’).
Show the causal chain: high biodiversity → complex food web → functional redundancy → stability.
Keep each point short and to the point, matching the 5‑mark structure.

Common mistakes

Mixing up ‘biodiversity’ with ‘species richness’ or ‘species diversity’.
Failing to mention the role of functional redundancy or the risk of collapse in low‑biodiversity systems.

Mark scheme (5 marks)

Greater biodiversity means more species are present / greater variety of species in the community
Food webs / food chains are more complex with more species, providing more feeding relationships
If one species is lost / becomes extinct, other species can fill its role / other food sources are available
This prevents / reduces the risk of other species dying out / going extinct if one species declines
Low biodiversity makes a community more vulnerable to disease / environmental change / loss of a key species causing collapse of the community

Key terms in this question

biodiversity · community