Scientists have found evidence that climate change is causing shifts in the seasonal timing of biological events, such as flowering in plants and egg-laying in birds. Explain how a mismatch in seasonal timing between a prey species and its predator could affect the population size of the predator over time.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Many migratory birds time their arrival and egg-laying to coincide with peak availability of insect prey. Rising global temperatures are causing insects to emerge earlier in spring, but some bird species have not adjusted their migration and breeding times at the same rate.
Model answer (5 marks)
Climate change causes insects to emerge earlier in the year, a phenological shift that changes the seasonal timing of prey availability.
The bird’s breeding or egg‑laying season does not shift at the same rate, creating a mismatch between the peak of insect abundance and the peak demand for food by the chicks.
During the critical growth period the chicks receive less food and are food‑deprived.
As a result fewer chicks survive, increasing offspring mortality and reducing the bird’s reproductive success.
Over successive generations the predator population size will decline because the birth rate falls below the death rate.
The bird’s breeding or egg‑laying season does not shift at the same rate, creating a mismatch between the peak of insect abundance and the peak demand for food by the chicks.
During the critical growth period the chicks receive less food and are food‑deprived.
As a result fewer chicks survive, increasing offspring mortality and reducing the bird’s reproductive success.
Over successive generations the predator population size will decline because the birth rate falls below the death rate.
Examiner tips
- Use the exact sequence: phenological shift → mismatch → food deprivation → reduced survival → population decline.
- Show the causal chain clearly; link each point to the next.
- Mention that the decline is due to lower reproductive success, not just immediate mortality.
Common mistakes
- Confusing the direction of the mismatch (e.g., saying chicks get more food).
- Failing to connect reduced survival to a lower birth rate and overall population decline.
- Using vague terms like “bad timing” instead of “phenological shift”.
Mark scheme (5 marks)
- Climate change causes insects to emerge earlier in the year (phenological shift / change in seasonal timing)
- The bird's breeding / egg-laying season does not shift at the same rate, creating a mismatch between peak insect availability and peak chick demand for food
- Chicks/offspring receive less food / are food-deprived during the critical growth period
- Fewer chicks survive / increased mortality in offspring, reducing reproductive success
- Over time the predator (bird) population size decreases / declines because birth rate falls below death rate
Key terms in this question
climate change · seasonal timing · mismatch · population size
Related
- All Pearson Edexcel A-Level Biology A (9BI0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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