Abiotic and Biotic Factors Affecting Communities — AQA GCSE Biology
Communities are affected by both non-living (abiotic) and living (biotic) factors.
Abiotic factors
Abiotic (non-living) factors that affect communities include:
- light intensity (affects photosynthesis and plant growth),
- temperature (affects rate of growth and enzyme activity),
- moisture levels,
- soil pH and mineral content,
- wind intensity and direction,
- carbon dioxide level (for plants), and
- oxygen level (for aquatic animals).
A change in an abiotic factor can affect the size of a population — for example, less light reduces plant growth, affecting the whole food web.
Biotic factors
Biotic (living) factors that affect communities include:
- availability of food,
- new predators arriving,
- new pathogens (disease), and
- competition — one species may out-compete another so its numbers fall.
Effect on populations
If an abiotic or biotic factor changes, populations can rise or fall. For example, a new predator can reduce a prey population; more food can increase a population.
Exam tips
- Distinguish abiotic (non-living) from biotic (living) factors with examples.
- Explain how a given factor would affect a population (e.g. less light → less photosynthesis → fewer plants).
- Remember oxygen level mainly matters for aquatic animals; CO₂ for plants.
- Competition and new predators/pathogens are biotic factors.