Interdependence

Ecosystems and material cycles · Communities and interdependence · note 3 of 4

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InterdependenceSpec 9.3

In short

Interdependence is the way species in a community depend on one another for food, shelter, pollination and seed dispersal. Because of this, a change to one population can affect many others. A community with many different species is more stable, because the loss of one species is less likely to cause the whole community to fail.

In a community, species depend on one another. This is interdependence. Organisms depend on other species for food, shelter, pollination and seed dispersal.

Animals depend on plants and other animals for food.
Plants depend on insects and other animals for pollination and seed dispersal.
Many species depend on trees for shelter and nesting sites.

Because of this, a change to one population can affect many others. If a species is removed or its numbers fall, species that feed on it may starve, while species it feeds on may increase in number. A community with many different species is more stable, because the loss of one species is less likely to cause the whole community to fail.

Exam tip:

When asked about a change in a food web, follow the effect through at least two steps: what happens to the species that eats it, and what happens to the species it eats.

Written and checked against the Edexcel GCSE Biology (1BI0) 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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