Explain how the concept of the realised niche differs from the fundamental niche, and outline one factor that can cause a species to occupy a realised niche smaller than its fundamental niche.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The fundamental niche is the full range of abiotic and biotic conditions under which a species could potentially survive and reproduce. The realised niche is the actual range of conditions and resources a species uses in the presence of biotic interactions such as competition or predation. The realised niche is therefore a subset of, or equal to, the fundamental niche because these interactions restrict the species’ actual use of conditions and resources. One factor that can make the realised niche smaller is interspecific competition, which can exclude a species from part of its potential resource range.
Examiner tips
- Define both niches clearly; state that realised is a subset of fundamental; give one specific factor (e.g. competition) and explain its effect.
- Use the exact terms ‘fundamental niche’, ‘realised niche’, ‘biotic interactions’ and ‘subset’ as per the mark scheme.
Common mistakes
- Confusing the two niches or saying they are the same; not specifying that realised is a subset; giving a factor that does not restrict the niche (e.g. a positive interaction).
Mark scheme (4 marks)
- The fundamental niche is the full range of abiotic and biotic conditions under which a species could potentially survive and reproduce.
- The realised niche is the actual range of conditions and resources a species uses/occupies in the presence of biotic interactions such as competition or predation.
- The realised niche is a subset of / smaller than or equal to the fundamental niche because biotic interactions restrict a species' actual use of conditions/resources.
- One factor causing the realised niche to be smaller than the fundamental niche, e.g. interspecific competition excludes a species from part of its potential range of resources; or predation restricts the times/places a species can feed; or parasitism reduces the conditions under which the host can survive.
Key terms in this question
fundamental niche · realised niche
Related
- All IB DP Biology Higher Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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