LWE: Lesson - Food Chains and Food Webs (Topic 1.11) 📖

⏳ Estimated Reading Time: 6 - 8 minutes

Learning Objective

Describe food chains and food webs, and their constituent members by trophic level.

 

Food Chains

Food chains describe how energy and nutrients flow from one organism to another. Energy moves “up” the food chain and the arrows in a food chain are ALWAYS drawn FROM the lower trophic level TO the higher trophic level.

a food chain with an arrow from the sun to grass to a caterpillar to a squirrel to an eagle. The grass is labeled "producer". The other organisms are labeled "consumers". There is an asterik that states that the arrow represents the flow of energy.
The caterpillar is eating the grass, so the arrow is drawn FROM the grass TO the caterpillar because the energy is moving FROM the grass TO the caterpillar.  The arrows in a food chain do not go the other way because plants do not eat insects (unless you have a carnivorous plant, which is a very special case).
 

Food chains seldom occur as isolated entities, but food chains are an easy way to think about the flow of energy, even though food webs are more realistic.

 

Food Webs

a food web showing the flow of energy between the sun, producers, and consumers. There is an asterisk that states "arrow represents the flow of energy"
This is a food web. You can see that it has many more arrows and involves many more organisms than a food chain.

Food webs link many food chains together. They can illustrate complex interactions between species in an ecosystem.  Some food webs can become so complicated that they look like a plate of spaghetti!

Because food webs can be very complicated, you will not be expected to draw a food web with EVERY organism that is present in an ecosystem. Of course, the more complete a food web, the more realistic the food web.  These are important because they can show us what happens when an organism is taken out of an ecosystem.           

The arrows in a food web are the same, however. They will always show the flow of energy from the SOURCE to the RECIPIENT.

Let's examine the food web below. Click through the parts of the food web and see if you can spot places where an organism is on two different trophic levels, depending on who is eating it:

Essential Knowledge

A food web is a model of an interlocking pattern of food chains that depicts the flow of energy and nutrients in two or more food chains.

 

Feedback Loops

A feedback loop is a process where the output of a system is fed back into the input, resulting in a cycle of cause and effect. Feedback loops can be positive or negative, depending on whether they amplify or dampen the changes in the system. Read through each tab to learn more about each type of feedback loop:

Negative Feedback Loops

A negative feedback loop is when a change brings about a change in the opposite direction.  This causes a system to return to its previous condition.  Most natural systems are negative feedback loops. Explore the examples of negative feedback loops below. Click on each white dot to move between the examples:

 


Essential Knowledge

Positive and negative feedback loops can each play a role in food webs. When one species is removed from or added to a specific food web, the rest of the food web can be affected.

 

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