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Tolerance curves – abiotic factors, limiting factors and zonation

BiologyEcology & EnvironmentAges 17–18

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Move sliders for temperature, light, soil water (or salinity) and pH to see that every species has its own range of tolerance: an optimum, an optimal range, zones of physiological stress and lower and upper limits (Shelford's law of tolerance). A land or shallow-sea community changes its cover over time, showing the dominant species and its limiting factor; indicator species help you work out the conditions at a mystery site. The zonation screen shows vegetation belts on a mountain set by temperature and bands of organisms on a rocky shore set by the tides.

Lesson: Abiotic factors and ranges of tolerance

What it shows

Each species can live only within a range of every abiotic factor, between a lower and an upper limit. Near the optimum it grows and reproduces best; in the zones of physiological stress it survives but is scarce; beyond the limits it cannot live. Shelford's law of tolerance says that a species' presence and abundance are set by the factor it tolerates least well, the limiting factor. Species with narrow ranges are good indicators of conditions. Where a factor changes gradually across space, such as temperature up a mountain or exposure on a rocky shore, species form distinct zones.

How to use

In Tolerance curve, choose Species A, Species B and Factor, then drag on the graph or use the slider. In Community, move the four sliders or pick a habitat from Set conditions like and watch the cover change; try Mystery site, then Show conditions. Tick Competition between species. In Zonation, choose Mountain or Rocky shore and drag the red line.

Parameters you can change

  • Screen Tolerance curve, Community and limiting factor, Zonation by altitude or on a rocky shore
  • Habitat Land (plants), Shallow sea
  • Temperature -10–45 °C
  • Light (% of full sunlight or of surface light) 0–100 %
  • Soil water (0 = bone dry, 100 = waterlogged) 0–100 %
  • Salinity 0–45 g/kg
  • pH (soil or seawater) 3–10
  • Species A (tolerance curve screen) Prickly pear cactus (Opuntia), Heather (Calluna vulgaris), Bog moss (Sphagnum), Rice (Oryza sativa), Wheat (Triticum aestivum), Wood sorrel (Oxalis acetosella), Common reed (Phragmites australis), Dandelion (Taraxacum officinale), Reef-building coral (Acropora), Giant kelp (Macrocystis pyrifera), Eelgrass (Zostera marina), Blue mussel (Mytilus edulis), Clownfish (Amphiprion), Atlantic cod (Gadus morhua)
  • Species B for comparison No comparison, Prickly pear cactus (Opuntia), Heather (Calluna vulgaris), Bog moss (Sphagnum), Rice (Oryza sativa), Wheat (Triticum aestivum), Wood sorrel (Oxalis acetosella), Common reed (Phragmites australis), Dandelion (Taraxacum officinale), Reef-building coral (Acropora), Giant kelp (Macrocystis pyrifera), Eelgrass (Zostera marina), Blue mussel (Mytilus edulis), Clownfish (Amphiprion), Atlantic cod (Gadus morhua)
  • Factor on the horizontal axis Temperature, Light, Soil water, Salinity, pH
  • Competition between species
  • Zonation Mountain (altitude), Rocky shore
  • Temperature change from today (mountain) -3–6 °C
  • Spring tidal range (rocky shore) 1–10 m
  • Wave exposure (rocky shore) 0–100 %

Questions to explore

  1. Why does a narrow-tolerance species such as heather tell you more about the soil than a dandelion does?
  2. Which factor limits wood sorrel on farmland, and why does raising the other factors not help?
  3. How does a marine heatwave of a few degrees push reef-building corals outside their range of tolerance?

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