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C4.1.6—Negative feedback control

Negative feedback 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
C4.1.6
Level
HL

Exam analysis

Chance of appearing1%of analysed past papers
Latest appearanceMay 2023
Most common paperPaper3
Typical marks2

Common command terms

  • Identify
  • Explain

Scoring notes

Common mistake
Confusing a population with a community or with all organisms in an ecosystem.

Recent exam appearances

May 2023Paper3 ["HL"] · TZ116(b)[ 2 ]C4.1.6—Negative feedback control

Coverage 2023–2023 · Updated 16 Jul 2026

Density-Dependent Feedback Opposes Departure from Capacity

population density rises → competition, pathogen transmission, waste effects or predation intensify → birth rate falls and/or death rate rises → net growth falls → density moves back toward K

Factor Density-dependent? Regulatory pattern
competition, disease, predation yes effect becomes stronger as density rises
drought, frost, fire or storm usually no can change population size regardless of density

‘Negative’ describes opposition to change, not harm. The result is often fluctuation around K rather than a perfectly constant population.

A rabbit and lynx cycle represents higher prey density supporting more predators, which then lowers prey density before predator numbers decline.

Estimate the Population, Then Explain Its Change

define the population → choose a representative design → sample sessile or motile organisms appropriately → calculate an estimate → test assumptions and uncertainty → follow size through time → explain slope and fluctuations using limiting factors and feedback

Evidence pattern First question to ask
quadrat estimate differs between repeats were placement, sample number and habitat structure representative?
few marked animals are recaptured is the population large, or were marks lost / mixing poor?
growth slows near a plateau which density-dependent factor is strengthening?
population drops far below K after a storm is a density-independent disturbance responsible?

A population number becomes biologically useful only when the sampling inference and the mechanism of change are both explicit.

Negative feedback control

[ 2 ]

Explain the change in numbers of the cactus moth throughout the study period.

Concept essentials

  • Negative feedback control must be linked to the correct ecological unit, method or species interaction.
  • The evidence for negative feedback control depends on measurable abundance, distribution, survival or resource patterns.
  • Negative feedback control is clearest when cause, ecological process and population outcome are kept distinct.
  • Field or graph evidence for negative feedback control needs biological interpretation, not values alone.