Explain why removing all the top predators from an ecosystem would affect the populations of other organisms in that ecosystem.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
In some parts of the world, large predators such as wolves have been hunted and removed from ecosystems. This has had significant effects on many other species living there.
Model answer (4 marks)
Top predators are consumers that feed on other animals, so they keep prey populations in check.
If all top predators are removed, prey numbers rise because there is no predation pressure.
The larger prey population competes more intensely for food and space, which limits the growth of other prey species.
The over‑grazing or over‑foraging by the abundant prey reduces the amount of plant biomass available, so the populations of producers and any organisms that depend on them decline, disrupting the whole food chain.
If all top predators are removed, prey numbers rise because there is no predation pressure.
The larger prey population competes more intensely for food and space, which limits the growth of other prey species.
The over‑grazing or over‑foraging by the abundant prey reduces the amount of plant biomass available, so the populations of producers and any organisms that depend on them decline, disrupting the whole food chain.
Examiner tips
- Use the word ‘control’ or ‘regulate’ when describing predators’ role.
- Show the chain: predator → prey → competition → producers → other species.
- Mention that the effect is indirect but still significant.
Common mistakes
- Confusing predators with prey or saying predators ‘grow’ instead of ‘control’ populations.
- Omitting the step that increased prey leads to competition for resources.
- Failing to link the decline in producers to the impact on other species.
Mark scheme (4 marks)
- Top predators are consumers that feed on other animals (prey species), controlling their population size
- Without top predators, the prey population would increase / not be kept in check
- An increase in prey population leads to greater competition for food / resources among prey organisms
- This reduces the population of producers / plants, which affects other organisms that depend on them (or vice versa — named organisms further down the food chain are affected)
Key terms in this question
top predator · population · ecosystem
Related
- All WJEC GCSE Biology (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →