Choose what type of ecosystem you will simulate. Different choices include an ocean, rocky shore, indigenous forest, grassland or pond. Research what types of plants, trees and animals live in the ecosystem you have chosen and how these things interact with each other. Begin drawing the background of the landscape. Draw animals on a separate sheet of paper and color them in with markers or crayons. Cut out the animal shapes and glue them onto the background. Position the animals interacting with each other the way they would in nature. Draw arrows to show the interactions.
Cut the tops off two milk cartons. Punch three holes into the bottoms of both cartons. Use a marker to label one carton "A" and the other "B." Fill three-quarters of each carton with loosely packed soil. Plant three radish seeds, 1 cm apart, in carton "A." Plant 20 radish seeds, 1/2 cm apart, in carton "B." Place the cartons in an aluminum pan and add a cup of water to each. Add water every three days to keep the soil damp. Instruct students to observe the difference in the way the plants grew in the two cartons. Explain how overcrowding can harm an ecosystem.
Cut out 200 small squares of paper to represent rabbits (prey) and 50 large squares of paper to represent coyotes (predators). Toss three rabbits onto a table. Toss one coyote onto the table. The coyote will need at least three rabbits to survive, so if the paper does not land on all three rabbits it must be removed from the table. Remove the rabbits that the coyote touched when landing on the table. Use a new coyote for the next round if the first one did not survive. The prey population doubles with every generation. You will notice after a few rounds that the number of prey far exceeds the number of predators.
Have students draw a picture of an ecosystem. Use scissors to cut a 4-inch slit somewhere on the page. Instruct students to swap drawings with a partner. Once the partner has examined the ecosystem, have her draw an animal that does not belong in that ecosystem. Cut out the animal and glue a craft stick to the back. Insert the animal into the drawing's slot. Have students ask and answer questions about how this foreign animal might affect and be affected by this ecosystem.