QUESTION 126 (6 marks)
A closed population is monitored in a habitat with limited food. Extra food becomes continuously available on day 10 and remains available. The graph shows the response; no other condition is deliberately changed.
a) Estimate the population sizes at the earlier and later plateaus. [2 marks]
b) Calculate the percentage population change from day 10 to day 15. [2 marks]
c) Explain how added food could produce the changed plateau. [2 marks]
Practice marking scheme
Answer
The earlier plateau is near 100 and the later plateau near 200. From day 10 to 15, increase is 80 and the five-day per-capita change is 80%. More food can increase carrying capacity by reducing resource limitation.
Working
The population is about 100 on day 10 and 180 on day 15. Change is 80; dividing by the initial 100 gives 0.80 or 80% over that five-day interval. The later stable level is near 200 rather than 100. Carrying capacity depends on available resources and need not remain fixed after the habitat changes.
Marking criteria
- Estimates earlier plateau about 100. [1 mark]
- Estimates later plateau about 200. [1 mark]
- Uses increase 180 − 100 = 80. [1 mark]
- Calculates 80% over the five-day interval. [1 mark]
- Links additional food to reduced resource limitation or competition. [1 mark]
- Explains that more individuals can be supported, increasing carrying capacity. [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.