Food Webs & Interdependence IGCSE Biology

Food Webs and Interdependence: Connected Feeding Relationships

Biology editorial review is supported by the named review panel. Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.

Key concept

A food web shows interconnected food chains in an ecosystem. Organisms depend on each other for food, so a change in one population affects others. If a prey species decreases, its predators may decrease and its competitors may increase.

Food web questions test the ability to trace cause and effect through multiple connected food chains. Students must predict the knock-on effects of adding or removing a species, considering both direct and indirect relationships.

Food webs vs food chains

A food chain shows a single linear pathway of energy transfer. A food web shows all the interconnected food chains in an ecosystem, providing a more realistic picture of feeding relationships because most organisms eat more than one type of food and are eaten by more than one predator.

Food webs show that ecosystems are complex, with many interdependent relationships. A change in the population of one species can have effects that ripple through the entire web.

Predicting the effects of population changes

When a species is removed from or added to a food web, the effects depend on how many connections that species has. To predict effects, trace the connections:

If a prey species decreases: its predators may decrease due to less food, and organisms that competed with it for food may increase due to reduced competition. If a predator is removed: its prey may increase because fewer are eaten, which may then reduce the food sources of the prey through overgrazing.

Always consider both direct effects (immediate predator-prey links) and indirect effects (knock-on consequences further along the web).

Interdependence explained

Interdependence means that organisms in an ecosystem depend on each other for survival. This includes feeding relationships (food webs), but also other interactions such as pollination (plants depend on insects, insects depend on nectar), seed dispersal (plants depend on animals), and shelter (organisms depend on habitats created by other species).

Because of interdependence, the loss of one species can have consequences for many others. Keystone species are those whose removal would cause a disproportionately large change in the ecosystem, even if they are not the most abundant species.

Try a focused question (3 marks)

In a food web, rabbits eat grass and are eaten by foxes and hawks. If a disease kills most of the rabbits, predict and explain the effect on the fox population.

Show the answer and marking guidance

Foxes would have less food available because rabbits are a food source.
The fox population would decrease due to increased competition for reduced food.
Foxes that cannot find enough food may die or fail to reproduce, reducing the population further.

Original Cambridge-style practice written for this site. It is not an official Cambridge past-paper question.

Common mix-ups to avoid

Check these points against your own answer before moving on.

Only considering direct effects and ignoring indirect ones.
Saying a predator population increases when its prey decreases.
Forgetting that many organisms eat more than one type of food, so the effect may be less severe if alternatives exist.
Confusing competition (organisms competing for the same resource) with predation (one organism eating another).