• Pencils
• Straightedges
• Drawing paper
• Scissors
• Glue

Procedure

1. Have each student draw a large triangle, a rectangle, a circle, and a square on a sheet of drawing paper. All four shapes should fit on one sheet. Cut out each shape. Write the word “carnivore” on the square. Write the word “herbivore” on the triangle. Write the word “producer” on the circle. Write the words “large carnivore” on the rectangle.
2. Have each student place the four paper shapes on a sheet of drawing paper in an order that forms a food chain. Draw arrows to show what each of the members eats.
3. Explain what a food chain might look like in a nearby river or lake. On a chalkboard, generate lists of local animals and plants under the producer, herbivore, carnivore, and large carnivore heading. Let the students label their shapes again with the name of an animal or plant of their choice.
   Producers: Phytoplankton, algae, aquatic plants, cattails, duckweed, trees.
   Herbivores: Ducks, geese, small fish, zooplankton, tadpoles, mayfly nymphs, small crustaceans.
   Carnivores: Sculpin, alewife, small fish, turtles, frogs, toads, water snakes, dragonfly nymphs.
   Large carnivores: Lake trout, walleye, bass, herons, gulls, red tailed hawks, humans.
4. Pretend that a disease, human influence, or overfishing has killed the carnivores in your chain. Have the students remove the square from their chain. Ask questions about interrelatedness to guide discussion and exploration.
   • If large carnivores such as walleye in Saginaw Bay are reduced by overfishing, nutrient enrichment, or parasitism, what happens to small fish, zooplankton, and phytoplankton populations? (The food chain will be disrupted in a chain reaction. First, the small fish population will increase because the walleye are not eating them. Second, the zooplankton population will be greatly depleted because of small fish eating them, and third, the phytoplankton population will increase because the zooplankton are not there to eat them.)
   • If great blue herons along the Grand River are reduced, what happens to water snake and aquatic plant populations? (This food chain will also be disrupted in a chain reaction. First, the water snake population will increase, and second, the water snakes will eat and deplete herbivores. Third, since the herbivores have been depleted, aquatic plant populations will increase.)
5. Optional for grades 7-8. Pretend that chemical pollution or another human influence, such as salt pollution due to snow removal from streets, has killed the producers in your chain. Remove the circle. Ask questions about interrelatedness to guide discussion and exploration.
   • If toxic chemicals reduced the growth and production of phytoplankton, what happens to the chain? (This food chain will be unable to support large numbers of animals.)
   • If city sewage gets into Lake St. Clair and provides too many nutrients for phytoplankton and aquatic plants, what happens to the food chain? (There is an over production of phytoplankton and aquatic plants. Some animals do well in these conditions, and some die, changing the food chain. Some waters will turn into a soupy green slime, and dead aquatic plants may end up on the beaches in unpleasant amounts.)