QUESTION 56 (5 marks)
A reserve supports a herbivore population. A prolonged drought begins at month 8. The table records the carrying capacity estimated from resource availability.
a) Describe how drought changed the carrying capacity. [1 marks]
b) Explain two mechanisms by which drought could cause this change. [2 marks]
c) Explain why a population of 480 animals at month 8 might decline even if no predators are present. [2 marks]
Practice marking scheme
Answer
a) It falls from 500 to 300. b) Less drinking water and less plant food can reduce supportable abundance. c) The population exceeds the later carrying capacity, increasing resource competition.
Working
Reduced rainfall can lower water availability and plant growth. Both reduce the number of herbivores the habitat can support. At 480 animals the population exceeds the later estimate of 300; competition can reduce births and/or increase deaths, producing negative net growth without predation.
Marking criteria
- Identifies the decrease from 500 to 300. [1 mark]
- Explains a reduction in water availability. [1 mark]
- Explains reduced plant growth/food availability. [1 mark]
- Recognises that 480 exceeds the later carrying capacity. [1 mark]
- Links resource competition to lower births and/or higher deaths. [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.