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C4.1.17—Top-down vs. bottom-up control

Top-down versus bottom-up control explains how ecological evidence links organisms, resources and interactions to population size, distribution or community structure in a habitat.

Syllabus
First assessment 2025
Objective
C4.1.17
Level
SL

Concept essentials

  • Top-down versus bottom-up control must be linked to the correct ecological unit, method or species interaction.
  • The evidence for top-down versus bottom-up control depends on measurable abundance, distribution, survival or resource patterns.
  • Top-down versus bottom-up control is clearest when cause, ecological process and population outcome are kept distinct.
  • Field or graph evidence for top-down versus bottom-up control needs biological interpretation, not values alone.
ConceptIB Biology SL