UNIT 3 FOOD CHAINS AND FOOD WEBS

3.1 Introduction

Living organisms that live together in an environment are interdependent.

These living organisms include plants, animals and humans.

But the environmental conditions, e.g. soil, water and climate also play an important

role. Ecosystems vary in size. Examples are the Kruger National Park, Kalagadi, the

Botanical gardens and the Gariep dam.

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Quick facts: The study of living organisms and the places where they live is called ecology.

There are various habitats in an ecosystem.

Examples:

A cheetah’s habitat is grasslands.

Mopanie worms’ habitat are mopanie trees.

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Ecosystem: An area where living (biotic) and non-living (abiotic) things live and interact with each other.

Biodiversity: The diverse spectrum of life found in one habitat.

Habitat: The area in which plants and animals live.

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Various plants and animals can be found in each habitat.

The plants and animals in a habitat depend on each other for food and protection

and they form a community.

Communities consist of a variety of populations, such as herds of kudu, flocks of sparrows and schools of fish.

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Community: All the living things in one habitat.

Population: One kind of living organism that is found in one habitat.

3.2 Food chain

Example of a food chain:

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Sun provides energy.

Plants (producers) use this energy to produce their own

food.

Grasshopper (primary consumer) eats the grass.

Frog (secondary consumer) eats the grasshopper.

Frog is eaten by the snake (tertiary consumer).

Snake is then eaten by the falcon.

After the falcon dies, its body is broken down by detritivores and decomposers and

energy is released into the soil, atmosphere and water.

Energy is transferred from one organism to the other in this manner.

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Food chain: It is the relationship where energy (in food) flows between living organisms.

Quick facts: A food chain always has producers and consumers.

Circulation of nutrients :

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Consumers: * primary * secondary * tertiary

Producers

Eaten by Die and are decomposed by

Die and are decomposed by

Detritivores and Decomposers

Consumed by

Used in photosynthesis Nutrients

3.3 Food webs

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Food web: A variety of interlinked food chains.

Various food chains and how they are linked:

• Worms, grasshoppers, mice, guinea fowls and antelope eat grass and plants.

• Herbivores are a source of food for various predators, carnivores and omnivores.

The grasshopper is eaten by the frog and the bird.

The snake catches the mouse.

The genet catches the mouse, frog, guinea fowl, bird and snake.

The antelope is eaten by the leopard.

The genet, guinea fowl and bird are eaten by the eagle.

Because the food chains overlap, a food web exists.

Decomposers are always at the top of the food chain or food web.

Decomposers recycle the nutrients in dead plants and animals and plough it back

into the soil.

These nutrients will make the soil fertile and make it possible for plants to grow.

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Activity 13

Investigate your area. See how many different food chains you can identify and

write them down. Food chains in my environment:

Seed → pigeon/mouse → cat/owl

Flowers → butterfly/moth → spider/gecko → crow

Flowers → plant louse → ladybug → spider → crow

Crops → snale → corn cricket → woodpecker

Crops → mouse → cat/owl

Leaves → worms → hoopoe → cat

Determine how many of these food chains are connected, and then draw your own

food web.

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Seed Flowers Crops Leaves Pigeon Mouse Butterfly Moth Plant-louse Snail Worms

Spider Ladybug Corn cricket Hoopoe

Gecko Wood pecker Cat Crow Owl