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B4.1.4—Range of tolerance of limiting factor

Tolerance ranges explain distribution because organisms perform best near optima and decline near critical minimum or maximum environmental limits of survival.

Syllabus
First assessment 2025
Objective
B4.1.4
Level
SL

Exam analysis

Chance of appearing5%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper2
Typical marks1–2

Common command terms

  • Evaluate
  • Deduce
  • Outline
  • Identify
  • Calculate
  • Analyse
  • Predict

Scoring notes

Common mistake
Treating a weak correlation or captive study as conclusive proof of distribution in the wild.

Recent exam appearances

November 2025Paper2 ["SL"] · TZ11(f)[ 2 ]B4.1.4—Range of tolerance of limiting factor
November 2025Paper2 ["SL"] · TZ11(e)[ 3 ]B4.1.4—Range of tolerance of limiting factor
November 2025Paper2 ["SL"] · TZ11(c)[ 1 ]B4.1.4—Range of tolerance of limiting factor
November 2025Paper2 ["SL"] · TZ11(b)[ 1 ]B4.1.4—Range of tolerance of limiting factor
November 2025Paper2 ["SL"] · TZ11(a)[ 1 ]B4.1.4—Range of tolerance of limiting factor

Coverage 2012–2025 · Updated 15 Jul 2026

A Tolerance Curve Has an Optimum, Stress Zones and Limits

For one environmental factor, a species has a critical minimum and maximum. Performance is highest near an optimum and declines through zones of physiological stress toward either limit.

Static tolerance curve with abundance on the y-axis and one abiotic factor on the x-axis. Label critical minimum, critical maximum, lower stress zone, optimum zone, upper stress zone, and intolerance beyond both limits.

choose an x-value → locate performance on the curve → classify optimum, stress or intolerance → remember another factor may still prevent the species occurring

Coral Reefs Require Several Conditions at Once

Reef-building corals depend on warm, shallow, clear, well-lit seawater with suitable salinity and carbonate chemistry. Photosynthetic symbionts supply much of the energy supporting calcification.

Coral reef system diagram showing shallow sunlit water, coral polyps with zooxanthellae, clear water column, saline seawater, and side arrows indicating limiting factors such as sediment, reduced light, cold upwelling, and lower pH.

greater depth or turbidity → less light
thermal stress → bleaching risk
lower pH → harder CaCO₃ deposition
sediment/nutrient disturbance → damaged or shaded coral

Summary: Predict Distribution from Environment and Adaptation

measure environment → locate tolerance limits and optimum → predict possible distribution → test abundance in the field → explain how adaptations change performance

microhabitat: local moisture, light and temperature
species range: interacting tolerance, adaptation and dispersal limits
biome: long-term climate filters whole communities; similar pressures can produce convergent forms

Range of tolerance of limiting factor

[ 2 ]

Using the data in the graphs, discuss whether species in Group 1 or Group 2 are more likely to be adversely affected by increases in soil temperature due to global warming.

Concept essentials

  • Organisms have ranges of tolerance for abiotic factors.
  • Performance is highest near the optimum zone.
  • Zones of stress reduce growth, survival or reproduction.
  • Critical limits can exclude organisms from habitats.
  • Tolerance evidence must be evaluated using the strength and limits of the data.