Tolerance ranges explain distribution because organisms perform best near optima and decline near critical minimum or maximum environmental limits of survival.
Coverage 2015–2024 · Updated 15 Jul 2026
A tolerance range extends from a critical minimum to a critical maximum for one limiting factor, with an optimum zone between zones of physiological stress.
Near the optimum, survival, growth, reproduction or abundance is highest. Toward either limit, stress lowers performance; beyond the limits the species is absent because it cannot persist.
Along a belt or line transect, record species abundance at regular positions and measure the chosen abiotic variable—such as temperature, light intensity or soil pH—with calibrated sensors. Replicate measurements and keep sampling effort consistent.
Plot abundance against the measured factor, look for an optimum and declining abundance toward both extremes, then report the direction and strength of any correlation rather than assuming causation.
Tolerance to one factor does not guarantee presence because another factor may be limiting. The optimum for growth may also differ from the optimum for reproduction.
This objective is assessed through structured response, commonly using Evaluate / Deduce / Outline.
Evaluate / Deduce / Outline / Identify / Calculate / Analyse / Predict
Build the answer around this relationship: Organisms have ranges of tolerance for abiotic factors.
Treating a weak correlation or captive study as conclusive proof of distribution in the wild.
Representative question
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.
A strong answer defines the place as a habitat or microhabitat, names the abiotic factor, and shows how it limits distribution through a tolerance range. Named examples then secure the marks: coral reefs require specific light, temperature, salinity, pH, and clear shallow water; biomes are predicted from temperature, rainfall, and insolation; desert and rainforest organisms show adaptations matched to their environmental pressures.
