Abiotic and biotic factors

Ecosystems and material cycles · Communities and interdependence · note 2 of 4

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Abiotic and biotic factorsSpec 9.2

In short

Abiotic factors are the non-living factors that affect a community, such as temperature, light, water and pollutants. Biotic factors are the living factors, such as competition and predation. Changes in either can change which species live in a community and how many there are. On a predator-prey graph, the predator peak comes after the prey peak.

The organisms in a community are affected by abiotic factors (non-living) and biotic factors (living). Changes in either can change which species live in a community and how many there are.

Factors that affect communities
Type	Factor	How it can affect a community
Abiotic	Temperature	Affects the rate of enzyme-controlled reactions, so growth and survival. Species survive only within a range of temperatures.
Abiotic	Light	Plants need light for photosynthesis. Less light means fewer plants, and so less food for the animals that depend on them.
Abiotic	Water	All organisms need water. In dry conditions only organisms adapted to save water survive, so numbers and variety fall.
Abiotic	Pollutants	Pollutants such as sulfur dioxide in air or sewage in water can kill sensitive species, reducing the variety of organisms.
Biotic	Competition	Organisms of the same or different species compete for the same limited resources, such as food, water, light and space.
Biotic	Predation	Predators eat prey, so predator and prey numbers affect each other.

Competition

Competition happens when organisms need the same resource and there is not enough for all of them. Plants compete for light, water and mineral ions. Animals compete for food, water and territory. The better-adapted species gets more of the resource, so it survives and reproduces more, and the numbers of the other species may fall.

Predation

In a stable community, predator and prey numbers rise and fall in a repeating pattern. When prey numbers rise, predators have more food, so predator numbers rise. More predators eat more prey, so prey numbers fall. With less food, predator numbers then fall, and the prey can recover.

Exam tip:

On a predator-prey graph, the predator peak comes after the prey peak, because predator numbers rise only once there is more food.

Line graph of population size against time showing prey and predator numbers rising and falling in repeating cycles, with the predator peak coming a short time after the prey peak. — Predator and prey numbers cycle: the predator peak comes after the prey peak.

Written and checked against the Edexcel GCSE Combined Science (1SC0) specification · Updated October 2026

Frequently asked questions

What is the difference between a population and a community?

A population is all the organisms of one species living in the same area, such as all the badgers in a wood. A community is all the populations of different species living in the same area. An ecosystem is a community together with the non-living, abiotic parts of its environment, such as soil, water and light.

What are abiotic and biotic factors?

Abiotic factors are non-living factors that affect a community, such as temperature, light, water and pollutants. Biotic factors are living factors, such as competition for food, water, light and space, and predation. A change in either type can change which species live in a community and how many of each there are.

Why does the predator peak come after the prey peak?

The predator peak comes after the prey peak because predator numbers rise only once there is more food. When prey numbers rise, predators have more to eat, so their numbers increase. More predators eat more prey, so prey numbers fall. With less food, predator numbers then fall, and the prey population can recover.

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