Experience 4: Food Webs

Topic: Youth will be introduced to concepts related to food web dynamics.

Time: This lesson should take approximately 45 – 60 minutes to complete.

Learning Outcomes

At the end of this activity, youth should be able to:

  1. Explain what a food web is and why it is important.
  2. Talk about what could happen if fish were removed from the food web.
  3. Explain what a food chain is and how it could relate to Maine river ecosystems.

Background Information for Facilitator

During this experience, youth will learn about food chains and how they can be used to form food webs. Food chains are introduced first because they are what make up food webs. A food chain is one example of how energy flows through the food web. An example of energy flow through a chain given to youth is portrayed below:

graphic of food chain
(Image Credit: Pixabay)
  • In this food chain example it can be seen how energy is moving in a linear fashion. Starting with the sun and ending with the eagle.
  • The energy transfer process starts with the sun and is transferred to the algae through the process of photosynthesis.
  • After the process of photosynthesis, mayflies will eat the algae which gives them energy.
  • Next salmon will consume the mayflies to get the energy.
  • This chain ends with the eagle consuming the salmon to get energy.
  • Decomposers are missing from this chain but are important to acknowledge as part of the whole food web cycle. Decomposers recycle dead material back into the environment by breaking it down into nutrients used by producers. Continuing the example above, when the eagle dies, its body would be broken down by decomposers like bacteria and insects into materials such as water, carbon dioxide, and minerals, fertilizing plant growth.

This food chain example includes ideas from previous experiences. This was intended to hopefully allow the youth to draw the connections between fish and invertebrates discussed during Experiences 2 and 3. When explaining the example food chain, it is important to remind youth that all energy for life comes from the sun. Plants get their energy from the sun through the process of photosynthesis. In the example, food chain algae is a producer because algae make their own food. Mayflies, salmon, and eagles are considered consumers because they can’t make their own food and have to eat other living things to get their energy. During this experience, it would be important to note some of the impacts that the removal of a species might have on a food web. For example, a good question for discussion would be what would happen if the salmon population was removed from Maine rivers? Many impacts would happen if salmon were removed from the rivers. One of these impacts would be less food supply for humans and other animals.

Materials

  • pictures of animals from Maine
  • Maine wildlife guide
  • ball of yarn
  • scissors
  • blank pieces of paper
  • pencils

Vocabulary

  • Food chain – One example of the flow of energy through a food web
  • Food web – A collection of food chains together to show many routes for the flow of energy
  • Decomposers – Decomposers break down material that was once alive and release nutrients back into the environment

Methods

Part 1: Introducing the flow of energy

  • Have students start thinking about food web-related ideas by having them answer the following questions:
    • What food did you have for breakfast today?
  • Use what the students tell you to give an example of how energy flows.

Facilitator Note: This conversation could look something like this:

  1. After asking the youth what they had for breakfast, ask them
    1. “Why do we eat breakfast?”
  2. Give them a chance to think about the question and try to help them reach an answer similar to getting energy for the day. Next, ask the youth:
    1. What is cereal made from?
  3. Give the youth a chance to think and come up with an answer. Then explain that cereal is made from a lot of things, but they all start from grains like wheat, rice, or oats.
  4. Next, explain to the youth that grains are plants and ask them:
    1. Do you know how plants get their energy?
  5. After giving the youth some time to think about the question, explain that plants get their energy from the sun through the process of photosynthesis.

Part 2: Food Chains

  • Next, introduce the idea of a food chain. Explain that a food chain is an example of the flow of energy in a linear fashion usually starting with the sun. Note that they started to make a food chain when talking about what they had for breakfast. Energy started from the sun which went to the cereal and then was consumed by them for breakfast.
  • Expand the discussion by applying what was just learned about food chains to how it works for fish and invertebrates. The sun gives energy to algae which live in the river.  Then the algae is eaten by the invertebrates that we looked at earlier. Fish eat the invertebrates and other things from the river, and then the eagle consumes the salmon from the river. Decomposers are missing from this chain but are important to acknowledge as part of the whole food web cycle. Decomposers recycle dead material back into the environment by breaking it down into nutrients used by producers. Continuing the example above, when the eagle dies, its body would be broken down by decomposers like bacteria and insects into materials such as water, carbon dioxide, and minerals, fertilizing plant growth. Model this process using the pictures provided to make the food chain.
graphic of food chain
(Image Credit: Pixabay)

Part 3: Food Webs

  • Now that youth are familiar with talking about food chains it’s time to introduce the idea of food webs.
  • Food webs are more complex than food chains. They are essentially a bunch of interconnected food chains. Explain that this is what the youth are going to be modeling today, making up simple food chains and expanding them to food webs.
  • Start by placing all of the pictures of Maine species on a table with the sun in the middle. Then task the youth with making food chains starting with the sun.
  • The youth will take a piece of yarn and they will tape from the sun to another part of the web demonstrating the flow of energy. Next, they will connect the plant they connected to the sun to another animal. Youth will take turns doing this until they have made what looks like a web.
various food web images spread out on a table
Food web images (Photo Credit: Tyler Tibbetts)
  • Explain that this is the food web mentioned before made of all the smaller food chains. During the process discuss how some species are more connected to other species than others and what this could mean.
  • Next, hand out the Maine wildlife guides and ask the students what Maine species they might be interested in adding to the web. Have the youth decide in groups up to 5 species they would like to add. After adding the new species to the web, the youth should try to determine how they would fit them into the already existing web.
  • Once the web is constructed the facilitator will help model what it would look like if one of the species was removed from the web and the impacts that it would have on the rest of the web.
  • Ask the youth questions before moving on to the next part of the activity:
    • Which picture has the most yarn on it?
    • What does it mean when the picture has so many yarn connections?
    • What would happen if the fish or invertebrates were removed from the food web? Give them a chance to reason out what would happen with the yarn ecosystem.
    • What would happen if a fire burned down all the trees?
    • What would happen if the sun wasn’t there?
  • These scenarios can be modeled by flipping over the picture of the fish and seeing how the species connected to the fish would be affected. The same process can be done with the trees and the sun. After explaining the scenario to the students, give them a chance to reason out what would happen to the food web.

Part 4: Reflection

  • After completing the experience here are some reflection questions to consider:
    • Why might it be important that we are trying to restore salmon populations in Maine?
    • Are fish populations important? Why or why not?
    • Why should we be concerned about each kind of plant or animal?
    • Why is it important that we keep the invertebrates and fish happy and healthy? How could this benefit our community?
    • What could happen if the ecosystem or a food chain is disrupted?

Supplement to Experience #4: