5.12—Biotic and abiotic factors

Biotic factors are effects of living organisms, such as predation, competition, disease and food availability. Abiotic factors are non-living conditions, such as temperature, pH, salinity, light, humidity and oxygen concentration.

A species is abundant only where the combined conditions permit survival and reproduction. One factor can limit a population even when another factor is favourable.

A plant may be restricted to moist, low-salinity soil (abiotic) while herbivory or competition from another plant (biotic) further changes its abundance within that range.

Listing a factor does not show its effect. Link the factor to a mechanism and distinguish correlation in a habitat survey from a controlled causal test.