Explain how the ecological niche of a species can change over evolutionary time as a result of interspecific competition.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Darwin's finches on the Galápagos Islands show differences in beak morphology that are thought to have arisen partly through character displacement, a process in which competing species evolve to use different resources.
Model answer (4 marks)
Interspecific competition occurs when two species need the same or overlapping resources, which lowers the fitness of both.
Natural selection favours individuals whose niche or resource use differs from that of the competitor, because they experience less competition.
Over many generations heritable variation in resource‑use traits (e.g. beak size or shape) is selected for, producing character displacement and a shift in the species’ realised niche.
The end result is niche divergence or partitioning, allowing the two species to coexist by reducing overlap in their realised niches.
Natural selection favours individuals whose niche or resource use differs from that of the competitor, because they experience less competition.
Over many generations heritable variation in resource‑use traits (e.g. beak size or shape) is selected for, producing character displacement and a shift in the species’ realised niche.
The end result is niche divergence or partitioning, allowing the two species to coexist by reducing overlap in their realised niches.
Examiner tips
- Use the word "interspecific competition" first. Show the causal chain: competition → selection for different traits → niche shift. Mention heritable variation and character displacement. Finish with coexistence by niche partitioning.
Common mistakes
- Confusing niche with habitat. Forgetting to link competition to selection. Not mentioning heritable variation or character displacement.
Mark scheme (4 marks)
- Interspecific competition occurs when two species require the same or overlapping resources, reducing the fitness of both.
- Natural selection favours individuals whose niche / resource use differs from that of the competing species, as they experience less competition.
- Over generations, heritable variation in resource-use traits (e.g. beak size / morphology) is selected, leading to character displacement and a shift in the realised niche.
- The result is niche divergence / niche partitioning, allowing the two species to coexist by reducing overlap in their realised niches.
Key terms in this question
ecological niche · interspecific competition
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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