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Part XXII: The Interdependence of Living Things : The Ecosystem : An Interacting Community Index

Ecosystem Homepage
Energy in the food chain
Food webs
Competition Between Organisms
The Missing Link and the Control of Nature
Ecosystem example : The Rocky Shore
Ecosystem example : Milkweed : A Micro-habitat
Ecosystem example : The Trees in a Forest Canopy
Chapter Summary (useful for revision)
Questions relating to this chapter

Topic Chapters Index

 

Food chains

As the energy flows from one organism to another a food chain is established. Food chains may involve more than three organisms. The secondary consumer may become the prey of a tertiary (third) consumer, and so on. The last carnivore in the food chain is called the top carnivore. Food chains, however, are usually short; the fourth or fifth consumer is normally the top carnivore.

To understand why this limit on the number of consumers exists we need to study what happens to the energy as it flows along the food chain.

 

THE ECOSYSTEM: AN INTER-ACTING COMMUNITY

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The transfer of energy

The organisms which convert the energy of the sun into chemical energy, the producers, are called autotrophs. All green plants are autotrophs. Green plants absorb between 20% and 30% of the sunlight which reaches the Earth. Only 2% of the energy from the sunlight which reaches green plants is stored in the body of the plant.

The organisms which gain their energy by feeding on other organisms are called heterotrophs. Heterotrophs are either herbivores or carnivores or omnivores.

When the energy from the sun is converted into chemical energy by the producers, it is passed on to the consumers; first to the herbivores and then to the carnivores. Movement of energy from one organism to another is called energy flow.

 

Food chains

Mint plants © Paul Billiet

green plant(producer)

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Caterpillars © Paul Billiet

caterpillar (primary consumer)

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Crab spider with prey © Paul Billiet

crab spider (secondary consumer)

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Frog © Paul Billiet

frog (tertiary consumer)

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Heron, Costa Rica © Shirley Burchill

heron (top carnivore)

 

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