1. Introduction: Develop understanding of the sun as the source of all energy in the ecosystem.

What would happen to life on Earth if the sun stopped shining? Would humans and other animals survive without the sun? Review briefly with students that plants depend directly on energy provided by the sun to make their food and that, without the sun, animals would not have food (plants) to eat. Review the essential requirements for life. Animals need food, air, water, space, and nutrients (minerals usually from food). Plants need air, water, space, light, and nutrients. 

Show the students what you plan to eat for lunch today (example: chicken sandwich, piece of fruit, milk, and an oatmeal cookie). Trace the flow of energy back to the sun using one of the items in the lunch as an example (see following example.) Repeat the same procedure with additional items from the lunch.

Chicken-Corn-Sun

What was the same about all of the different foods in the lunch? What was the original source of energy that provided the energy that will be gained from eating the food? [Students should notice that all of the foods can be traced back to plants and that plants get their energy from the sun.] Ask students about other foods they eat and whether those foods can also be traced back to plants. Challenge the students to think of any food item that cannot be traced back to plants. [All foods can be traced back to green plants or to decomposing plants and animals.]

2. Define producer and consumer.

If plants get their energy from the sun, how do animals (including people) get their energy? [By eating plants and/or other animals that eat plants.] Introduce the terms producer and consumer. Producers obtain food by trapping light energy to make food and supply their energy needs (plants are examples of producers). Consumers obtain their food directly from other organisms by eating them (or being a parasite on or in them). Animals, including humans are examples of consumers. Ask students why they think scientists refer to these groups as producers and consumers.

Note: Each of the DNR posters has a small human on it. Gijsbert Frankenhuyzen, artist of the posters, painted himself into each of the posters. If you have extra time, challenge students to find him!

3. Introduce concept of decomposition.

What happens to the leaves that fall from the trees? To plants and animals when they die? To the wastes that animals (including people) produce? [Students should be able to respond that these materials eventually rot or decay.] Introduce the terms decomposition, decomposer, and scavenger. Decomposition is the process by which dead materials are recycled into soil or water by microscopic organisms such as bacteria, fungi, and microbes. Decomposers are the microscopic organisms that obtain their energy from dead material, and break it down into minerals and nutrients that can then be used again by plants. Examples include bacteria and fungi. Scavengers are larger organisms, like centipedes, earthworms, pill bugs, and vultures that consume dead material making the work of the microscopic decomposers easier. Scavengers are classified as consumers, although they can be considered part of the decomposer community. Without decomposers, the world would be covered with dead plants and animals!

Ask students to find (or suggest) examples of decomposers on their posters.

4. Develop the concept of a food chain using the MDNR posters.

What is the feeding relationship of the organisms on the posters? Review that an ecosystem can be defined as a community of organisms interacting with one another and the non-living environment. Within this community of living things (animals, plants, and microbes), many feeding relationships, or food chains, can be identified. Write the following example of a food chain on the board:

Sun --> Plants --> Insects --> Frog --> Snake -->Hawk

To help students recognize that some food chains involve decomposers, show students a second example of a food chain.

Dead Beech Tree --> Mushroom --> Deer

Explain that a food chain is a linear diagram that shows the order in which organisms feed upon one another. (The arrows show the flow of energy from producers to consumers.) Have students identify an example of a food chain on their poster, recording it in their unit journal or on a blank sheet of paper. Check for understanding by asking students for examples, making sure that the food chains are realistic. This may be a challenge for students who are not familiar with the eating habits of the animals shown on the poster.

Provide each group of students with the appropriate Who Eats What in Michigan Ecosystems chart (related to their poster) to help students identify feeding relationships among many of the organisms on the posters. Note that not all organisms from the posters are included on the charts.

Model for the students how to use the Who Eats What in Michigan Ecosystems charts to identify the feeding relationships among organisms. Show them how to use yarn and tape to indicate food chains on the DNR posters. Have students work in groups to identify as many food chains as possible. Students should try to make several (4-6) food chains at least three organisms long, using a new piece of yarn for each food chain.

Tell students to add organisms that they feel may be missing from the posters. For example, students should connect the plants to the sun, which may not be illustrated in all of the posters. Provide students with sticky notes or note cards on which they can illustrate and/or name any missing components. Discuss what students added to the poster. [Answers will vary.]

Option: Have students use small sticky-notes to label organisms in the food chains and to identify whether each is a producer, consumer, or decomposer.

5. Connect food chains to develop the concept of food webs.

Are any of the organisms on your poster part of more than one food chain? Explain that the food chains within a community link together to form a food web. What is the difference between a food chain and a food web? Explain that a food chain shows the transfer of food energy in one direction and from one organism in one level (producer) to one organism in the next level (herbivore.) The key is that the transfer is from one organism to another. Because so few organisms are involved, this can be an unstable relationship. A food web shows the connections between several food chains. Food webs involve many organisms providing a variety of energy paths. Organisms may have several food sources so that fluctuations in one population do not totally control fluctuations in another population.

Use additional pieces of yarn to link one food chain to another by connecting the appropriate organisms. Plants form the basis of most food webs. How might these food webs vary from season to season? [The amount of plants decreases, organisms migrate or hibernate, new organisms enter the system from other areas, etc.]

6. Tying it all together.

What would happen if one species in a food chain was eliminated/killed? Have each group think of a scenario where one type (species) of plant or animal is eliminated from the ecosystem and then predict its effects on the food web.

Examples of scenarios students might suggest:

• Forest poster:

      – A forest fire kills many trees.

      – All of the decomposers were eliminated.

• Wetlands poster:

      – The frogs disappear.

      – The blue herons disappear.

Have each group, working on their poster, take a pair of scissors and cut all of the strings that were linked to the species they chose to eliminate. Trace each string back to everything it was connected to and count/identify all of the organisms that were affected by the elimination of just one species. Students should conclude that elimination of any part of a food web can have far-reaching effects. For example, removing hawks from a forest food chain may result in an increase in the number of chipmunks living in the forest. The chipmunks in turn may eat larger numbers of beech tree seeds (beechnuts). With fewer tree seeds available, fewer trees may grow, affecting the entire forest ecosystem.

Will the populations of the affected organisms increase or decrease? Have students write a paragraph describing how the change would impact the food web on their ecosystem poster.

When making the assignment, share the rubric below to be used to evaluate student writing.

Display completed food chain posters and/or writing pieces in classroom.

Modification/Extension: Have student groups rotate through the different MDNR Non-game Wildlife Posters showing Michigan ecosystems, so that they can examine food webs in several ecosystems. Discuss which of the food webs are least/most complicated. Students may observe that the Jack Pine ecosystem food web is simplest, while the wetland ecosystem food web is most complex. Ask students to draw and label one food chain from each of the different ecosystems.