1. Understand the role of producers, consumers, and decomposers in an ecosystem. 2. Illustrate these relationships. 3. Describe the importance of the idea of “interconnectedness”.
Magazines/photos/printouts of various animals, plants, insects, from the ecosystem of your choice (local is best).
Poster boards (1 per group)
1. This lesson is intended to introduce or build the ideas of interconnectedness and interdependence as they apply to ecosystems. Begin by using some of the photos representing species from the ecosystem you have chosen to represent. Local is often best when introducing a concept like ecology as students are already familiar with species from their own experiences. Draw upon personal experience as much as possible when building these concepts, encouraging students to share personal stories about various plants, animals and insects.
2. Start with one photo. Its often best to start with the ‘coolest’ or most popular animal, such as a bear or a cougar. Put up the picture, and ask “what does this animal eat?” and “what eats this animal?” Keep asking until you have made a list of as many animals/plants/insects as possible. Put up their pictures, or, if you don’t have pictures for all of them, put up some pictures and write the names of others. Draw a line from the predator to each prey.
3. Now ask, for each of the new animals/plants/insects “What does this eat?”, put up the new photos/words, and continue until you have represented as much of the ecosystem as possible. Many animals will have multiple food sources. Try to indicate as many as possible. The students will probably get stumped on what plants eat. Set that idea aside for later. Don’t forget to include insects, and make sure that you include decomposers, such as bacteria and earthworms in the web.
4. Tell students that what they have just created is a food web. It is a model used by ecologists to illustrate how food is produced (made) and consumed (eaten) in an ecosystem. Talk about how plants use sunlight, water, and chlorophyll to make their own food, storing energy in their stems and leaves.
5. Start asking questions, and rephrasing the answers on the board for students to record as notes. Here are some sample questions to ask:
What is the root source of all food in the ecosystem? Which plants, animals, and insects make food, and which ones eat food? (Circle the producers in one colour of chalk and the consumers in another colour) What kinds of relationships can you see here? What would happen if we took one species out of the equation? (Illustrate by removing one animal/plant/insect at a time and speculating on how that would effect the web as a whole. Remove ten, and then discuss animals, plants and insects in danger, extinctions, and the repercussions of losing biological diversity in our ecosystems).
6. Now, you are going to reorganize the food web. On a neighbouring board or on a flip-chart write the word “PRODUCERS”. Have students come up, each finding one picture or word of a plant which produces food for the web, and moving it to form a horizontal line of producers beside the word. Now, above producers, write “PRIMARY CONSUMERS”. Explain that primary consumers eat only plants. Have students come up to find examples of species which only eat plants, and make a horizontal category of primary consumers. Continue for “SECONDARY CONSUMERS”, “TERTIARY CONSUMERS” and “QUATERNARY CONSUMERS”. Finish with the “DECOMPOSERS”.
7. Students now draw the model of production/consumption/decomposition in their notebooks.