Food Web

A food web is a complicated system of relationships between plants, animals, and energy. Understanding their connection is very important in helping to understand any ecosystem. Food webs are actually made up of smaller food chains, which are interconnected.

A food chain, explains what an organism might eat, and what might eat it in a specific scenario (there are usually hundreds of different possible food chains for an organism!). For example, a food chain could look like this:

SUN (energy)-> a plant (producer)-> a cow (herbivore)-> a person eating a hamburger

In a food chain, you can see that you lose energy as you go along the chain (the arrows represent the energy). So that is why there are so many more plants than animals, and more producers than herbivores and carnivores.

Can you think of some other possible food chains?

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Although a food web is not REALLY connected like a spider web, food webs are drawn in a diagram similar to a spider

web (with connecting arrows as the webbing) to show how the energy moves.

This picture is an example of a simple food web.

Most energy comes from the sun.

Plants, also called producers, convert that energy into food through a process called photosynthesis. Photosynthesis is a process which uses water, carbon dioxide, and sunlight energy to make sugars. Plants do this in special cells called chloroplasts. These are usually green because of a pigment called chlorophyll. Most photosynthesis happens in a plant's leaves, which is why they are green.

When an animal eats a plant, some of the energy gets passed from the plant to the animal. A food web shows this passage of energy, by showing what animals can eat what, and who gets eaten by whom!

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Food Web Activity Below are some pictures of organisms that can be connected into a food web. See if you can decide how to connect the pictures to show the energy flow correctly!

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Food Webs

Food chains are giving a simple picture of the feeding relationships between different living things. They are often too simple however. Most animals do not eat just one type of food. Humans for example eat a wide variety of different foods. Food chains are often inter-linked to create a more complex food web like the one shown below.

There are many food chains in the diagram above all intertwined. The following food chain shows five organisms.

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The food web gives us a better picture of the feeding relationships between different living things. We can also start to think about how changes in populations of one organism can affect the population size of other organisms. For example, let us look at what a sudden drop in the population of centipedes (perhaps due to disease) might have on the food web. Fewer centipedes means that there will be more beetles as fewer are eaten.

There will be a fall in the population of toads as their food source runs out, which has a knock on effect on foxes who will need to eat more rabbits as a result. Spiders will lose a food source and so their population will fall as will that of woodlice as spiders will need to eat more of them.

This shows that changing the size of a population of one organism can affect many others both directly and indirectly.

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Food Chains and Food Webs How does a change in the environment effect the plants and animals in that habitat?

Energy begins with the sun. It helps make the grass grow. The grass is a producer because it provides food for many animals. The grasshopper is a consumer and eats the grass. The snake consumes (eats) the grasshopper and is then eaten by the hawk. When the hawk dies, his body is broken down into nutrients (food) by fungi, which is a decomposer. This provides nutrients for the grass. The food chain is a cycle of energy.

A food web is made up of interrelated food chains. Many animals and plants share the same habitat and they all live happily together. Nature balances things so that the food webs last a long time. 6