# Explain how character displacement can occur when two species with overlapping ecological niches come into secondary contact after a period of geographic isolation.

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

## Mark scheme (4 marks)

1. When two species come into secondary contact, their niches overlap, leading to interspecific competition for shared resources.
2. Individuals whose phenotype/traits differ most from the competing species experience less competition and therefore have greater fitness/survival and reproductive success.
3. Natural selection therefore favours divergence of the trait/character in the zone of sympatry, causing the two populations to become more different from each other over generations.
4. The outcome is greater niche differentiation/partitioning between the two species in sympatry compared with allopatric populations, reducing competition and allowing coexistence.

## Key terms

- [character displacement](https://www.gradenine.co.uk/glossary/character-displacement)
- [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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-character-displacement-can-occur-fa7e173a) · Published by Druglandscape Ltd.