QUESTION 53 (4 marks)
Two grass species grow along a moisture gradient. When each is grown alone, both occur across the full gradient. When grown together, species P occupies wetter sites and Q occupies drier sites.
a) Explain the difference between a fundamental niche and a realised niche using species P. [2 marks]
b) Infer the interaction that most directly explains the pattern and describe how it restricts P’s distribution. [2 marks]
Practice marking scheme
Answer
a) P’s fundamental moisture range is the range it can occupy without the competitor; its realised range is the wetter range occupied with Q. b) Competition excludes or suppresses P in drier sites.
Working
The experiment indicates that P can tolerate the full moisture gradient in isolation. Its narrower distribution with Q reflects the effects of biotic interactions. Q may be a stronger competitor for a limiting resource in dry conditions, restricting P’s realised niche. The observation does not require P to have changed its underlying physiological tolerance.
Marking criteria
- Describes the fundamental niche using P’s full range when alone. [1 mark]
- Describes the realised niche using P’s occupied range with Q. [1 mark]
- Identifies competition. [1 mark]
- Links competition under dry conditions to restriction of P’s distribution. [1 mark]
Practice question aligned to the current QCAA syllabus; review the worked solution and marking criteria.
View the QCAA syllabusCompare your working with the guide above.