Explain how climate change may affect the timing of seasonal biological events, such as flowering and insect emergence, and how mismatches in these timings can affect ecosystem function.

IB DP Biology Higher Level (2023 syllabus) — D4.3 Climate change · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Rising temperatures advance the onset of spring, causing earlier bud burst, flowering and insect emergence.

Species respond at different rates; for example, plants may flower earlier than pollinators emerge, or caterpillars may appear before their host‑plant leaves are available.

This phenological mismatch reduces the overlap between resource supply and consumer demand, lowering reproductive success (e.g. fewer pollination events) and food availability for dependent species such as chicks.

Consequently, disrupted interactions weaken ecosystem stability, reduce biodiversity and impair ecosystem services such as crop pollination.

Examiner tips

  • Use the word ‘phenological mismatch’ and link temperature to earlier spring. Explain the cascade from reduced overlap to lower reproductive success. Mention specific ecosystem services affected.
  • Show the cause–effect chain: temperature → earlier phenology → mismatch → ecological impact.

Common mistakes

  • Confusing temperature with other climate variables (e.g. precipitation). Failing to mention that different species respond at different rates. Omitting the link to ecosystem services such as pollination.

Mark scheme (4 marks)

  1. Rising temperatures cause earlier onset of spring conditions, which triggers earlier flowering / bud burst / insect emergence / migration in many species.
  2. Different species respond to temperature change at different rates, so the timing of interdependent events (e.g. peak flower availability and pollinator activity) becomes uncoupled / mismatched.
  3. A phenological mismatch reduces the overlap between resource availability and consumer demand, leading to reduced reproductive success / decreased food availability for dependent species (e.g. chicks hatching after peak caterpillar abundance).
  4. Disruption of these ecological interactions (e.g. pollination, predator–prey cycles) can reduce ecosystem stability / biodiversity / ecosystem services such as crop pollination.

Key terms in this question

ecosystem function

Related

More Climate change questions

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