Describe how predation affects the size of a prey population, and explain what happens to the predator population as a result of changes in prey numbers.

Cambridge International IGCSE Biology (0610) — 19.4 Populations · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

When predator numbers increase, the number of prey eaten rises, so the prey population size falls.
A fall in prey numbers reduces the food available to predators, so the predator population subsequently declines.
When predator numbers fall, less prey are eaten and the prey population can recover and increase.
Thus predator and prey populations cycle together: prey numbers rise first, then predator numbers peak after the prey peak, and the cycle repeats.

Examiner tips

  • Use the word ‘decrease’ for prey when predators rise, and ‘increase’ for prey when predators fall. Show the causal chain: predator → prey → predator. Mention the lag between prey and predator peaks.
  • Use the exact terms ‘prey’ and ‘predator’ and avoid vague words like ‘animals’.
  • Include the idea that the populations are interdependent and cycle.

Mark scheme (4 marks)

  1. When predator numbers increase, prey population size decreases
  2. A decrease in prey numbers leads to a decrease in food supply for predators, causing the predator population to decrease
  3. A decrease in predator numbers allows the prey population to recover / increase
  4. The predator and prey populations cycle / fluctuate in a linked / interdependent way, with predator numbers peaking after prey numbers peak

Key terms in this question

population · predator · prey

Related

More Populations questions

▶ Try answering this question with AI marking (free) →