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.
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:
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
