FOOD CHAINS AND FOOD WEBS

Food chains and food webs describe feeding relationships. Organisms in an ecosystem affect each other’s population.

The table describes some common terms used to describe living things in their environment:

Term	Description
Environment	All the conditions that surround a living organism
Habitat	The place where an organism lives
Population	All the members of a single species that live in a habitat
Community	All the populations of different organisms that live together in a habitat
Ecosystem	A community and the habitat in which organisms live

A food chain shows what eats what in a particular habitat. It shows the flow of energy and materials from one organism to the next, beginning with a producer.

The Sun is the ultimate source of energy for most communities of living things. Green plants are usually the producers in a food chain.

Producers and consumers

A food chain always starts with a producer, an organism that makes food. This is usually a green plant, because plants can make their own food by photosynthesis.
The other organisms in a food chain are consumers, because they all get their energy by consuming other organisms. So a food chain ends with a consumer, an animal that eats a plant or another animal.

Here is an example of a simple food chain:

grass → cow → human

The arrows in food chains show the way in which energy is moving. They do not show what eats what.

Other words in a food chain

There are several words used to describe the organisms in a food chain. Study this food chain:

                

Organism	How it gets its energy
Consumer	Feeding on other organisms
Primary consumer	Eating plants
Secondary consumer	Eating primary consumers
Tertiary consumer	Eating secondary consumers
Herbivore	Eating plants
Carnivore	Eating other animals
Omnivore	Eating both plants and animals
Decomposer	Feeding on dead and decaying organisms, and on the undigested parts of plant and animal matter in faeces

Food webs

When all the food chains in an ecosystem are joined up together, they form a food web. Here is an example of a food web:

Although it looks complex, it is just several food chains joined together. Here are some of the food chains in this food web:

grass → insect → vole → hawk

grass → insect → frog → fox

grass → insect → vole → fox

Notice that:

·         the rabbits and slugs have just one predator

·         the frogs and voles have two predators (the foxes and hawks)

·         the insects have three predators (frogs, voles and thrushes)

This leads to some interesting effects if the population of a particular organism in the food web decreases. Some animals can just eat more of another organism if food is in short supply, while others may starve and die. This in turn can affect the populations of other organisms in the food web.

Here you have another example of a woodland food web:

The example above contains lots of information. Here are three food chains from it:

·         oak tree → squirrel → fox

·         oak tree → earthworm → wood mouse → fox

·         oak tree → earthworm → wood mouse → owl

The oak trees are the producers. Squirrels and earthworms are primary consumers, and the wood mice are secondary consumers. The foxes and owls are tertiary consumers (the foxes are also secondary consumers).

Foxes and owls eat the wood mice, and foxes eat wood mice and squirrels. The fungi and earthworms are decomposers in this food web.

You can find this information and more here, in BBC BiteSize