Abiotic variables such as temperature, water, light, pH, salinity, nutrients and substrate conditions strongly affect species distribution patterns in ecosystems.
Coverage 2018–2021 · Updated 15 Jul 2026
Abiotic variables restrict species distribution when their values fall outside the range in which individuals can survive, grow and reproduce.
Relevant variables include temperature, rainfall or water availability, humidity, light, salinity, pH, dissolved oxygen, mineral availability, wind or wave exposure and the physical substratum.
For a plant, light may limit photosynthesis and soil pH may alter mineral availability. For an animal, water temperature can alter metabolism, salinity affects osmoregulation and dissolved oxygen can constrain aerobic activity.
A freshwater animal may be absent from a saline estuary because salinity exceeds its tolerance even when food is abundant; a shade-intolerant plant may be absent beneath a dense canopy because light is below its requirement.
A mapped association does not prove one abiotic variable causes the distribution. Biotic interactions, dispersal history and covarying environmental factors may also explain abundance.
This objective is assessed through essay response, structured response, commonly using Outline / Describe / State.
Outline / Describe / State / Suggest / Discuss / Identify / Distinguish
Build the answer around this relationship: Abiotic factors are non-living conditions that affect organisms.
Listing abiotic factors without giving a biological reason for their effect.
Representative question
Discuss how abiotic factors can affect the distribution of species in an ecosystem.
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.
