Explain how both biotic and abiotic factors can affect the size of a population of rabbits living in a field.

OCR GCSE Biology A: Gateway Science (J247) — B4.1 Ecosystems · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Rabbits live in a field as part of an ecosystem alongside grasses, foxes and various pathogens. The size of the rabbit population changes throughout the year.

Model answer (4 marks)

1. Predation by foxes is a biotic factor that reduces the rabbit population by killing individuals.
2. Food availability is another biotic factor; when grass is scarce, rabbits have less nutrition, leading to lower survival and reproduction.
3. Temperature is an abiotic factor that affects the rabbit population.
4. High temperatures can reduce grass growth, decreasing food supply for rabbits, which in turn lowers rabbit numbers.

Examiner tips

Use specific terms (predation, food availability, temperature).
Show cause–effect links (predation → death, food scarcity → lower reproduction).
Keep each point short and to the point.

Common mistakes

Confusing abiotic with biotic factors, e.g. citing foxes as abiotic.
Failing to explain how the abiotic factor affects the ecosystem, e.g. not linking temperature to grass growth.

Mark scheme (4 marks)

A biotic factor such as predation (by foxes) reduces the rabbit population
A second biotic factor (e.g. food availability / pathogens / competition) also affects population size with a correct explanation
An abiotic factor such as temperature / light intensity / moisture / soil mineral content is correctly identified
Correct explanation of how the named abiotic factor affects the rabbit population, linked through its effect on the ecosystem (e.g. plant/grass growth)

Key terms in this question

biotic factors · abiotic factors