Explain how niche differentiation can arise between two populations of the same species that have become geographically isolated from one another.

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

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

Model answer (4 marks)

1. Geographic isolation stops gene flow between the two populations.
2. Each population is exposed to different selection pressures and environmental conditions.
3. Natural selection favours different adaptations or alleles, causing morphological, physiological or behavioural divergence.
4. Over time the populations occupy distinct ecological niches, using different resources or tolerating different conditions.

Examiner tips

Use the word "geographic isolation" first to show understanding of the starting point. Show the causal chain: isolation → different selection pressures → divergent adaptations → niche differentiation.

Common mistakes

Confusing isolation with competition; students sometimes say the populations compete rather than being isolated. Failing to mention that divergence is due to natural selection, not just random drift.

Mark scheme (4 marks)

Geographic isolation prevents gene flow between the two populations.
Each population experiences different selection pressures / environmental conditions in its respective habitat.
Natural selection favours different adaptations / alleles in each population, leading to divergence in morphology, physiology or behaviour.
Over time, the populations occupy different ecological niches as they use different resources, tolerate different conditions, or exploit different prey / food sources.

Key terms in this question

niche differentiation