Explain how the removal of a top predator from an ecosystem can affect the populations of organisms at lower trophic levels.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
In a grassland ecosystem, a food chain exists in which grass is eaten by rabbits, and rabbits are eaten by foxes. Foxes are the top predators in this ecosystem.
Model answer (4 marks)
Removal of the foxes removes the main predator, so the rabbit population is no longer controlled and increases.
The larger rabbit population feeds more heavily on the grass, so grass is eaten more rapidly.
The grass (producer) population therefore decreases.
This shows that a change in one trophic level (the top predator) can alter the populations of organisms at lower trophic levels, illustrating the interdependence of biotic factors in an ecosystem.
The larger rabbit population feeds more heavily on the grass, so grass is eaten more rapidly.
The grass (producer) population therefore decreases.
This shows that a change in one trophic level (the top predator) can alter the populations of organisms at lower trophic levels, illustrating the interdependence of biotic factors in an ecosystem.
Examiner tips
- Use the word ‘removal’ to show cause; link each level with ‘so’ or ‘therefore’; mention the trophic levels explicitly; keep answer concise and to the point.
Common mistakes
- Failing to state that the rabbit population increases; confusing the direction of the effect; not linking the decrease in grass to the increased rabbit numbers.
Mark scheme (4 marks)
- Removal of foxes means the rabbit population is no longer controlled / rabbit population increases (as predation pressure is removed)
- Increased rabbit population leads to greater consumption of grass / grass is eaten more rapidly
- Grass (producer) population decreases
- This illustrates that a change in one trophic level affects other trophic levels / biotic factors in an ecosystem affect population distribution
Key terms in this question
trophic level · predator · population
Related
- All Pearson Edexcel International GCSE Biology (4BI1) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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