1. Web of Life
Objective:
Students will understand the concept of a food chain and demonstrate a grassland’s food chain.
Materials:
- Pictures of animals, river, tree, grass, sun
- A ball of yarn/spool of twine
Procedure:
Read The Great Kapok Tree, by Lynne Cherry. Ask students to name all the different animals that are dependent on the one tree.
Give each participant a picture.
First demonstrate a food chain, a simple interdependence, by linking the student with the sun card (the source of all energy) to the student with the grass card to the student with the zebra card to the student with the lion card.
Show the impacts of man on the simple food chain. Man can:
- Cut trees (no trees, nothing for grazers to eat, grazers will die, lions and other predators will have nothing to eat. They will start to eat our livestock.)
- Hunt in excess (If we kill the lions, there will be too many zebras and they will need more grass. They will eat the grass from our pasturelands.)
Balance is key! Explain that the interactions in a grasslands system are more complicated than this. For example, the sun provides for more than just grass, and lions don’t only eat zebras.
Have the participants now stand in a circle, out of order (i.e. not all of the producers together, then the primary consumers, then the secondary consumers, etc.)
Give the ball of string to the person with the sun. Then ask that person to pass the yarn to the person with a card of an organism that the sun supports. If the sun supports more than one organism in the circle, pass the string back to the sun and from the sun to the other organism that it supports.
Continue by asking the plants which organisms they can support and so on.
Keep going through the chain until you get to the top consumers. The string will be a tangled web in the middle of the circle. Food chains are complicated, and the balance they create is essential.
Again discuss the impacts of man on the web by having students drop their string if man’s impact kills off their organism. For example, the impact of overhunting will cause the lions to drop their strings. What happens?
Possible Questions
- Do you know why there are more herbivores than carnivores?
- What if one animal from the food chain disappeared? What about one level of the food chain? Producers? Decomposers? Herbivores?
- How do humans fit in the food chain?
- What could happen if an animal not native to an area is brought into the local food chain?
- What could happen if you remove an animal from the food chain?
- How can sun and rain affect the food chain? Drought?
- Why is a food web a more accurate depiction of nature than a food chain or pyramid?
2. Food Chain Tag
This activity requires a large open area. In a class of 25 to 40 students, choose three to five to be predators and seven to ten to be plant-eaters. The remainder will be plants. This represents a balanced system where plants are more plentiful than plant-eaters, plant-eaters more plentiful than predators, and predators are the least plentiful. The students can select which plant-eaters and predators will be in their groups. (Example: Grevy’s zebras are plant-eaters and lions are predators).
Each group selects hand-signals that will differentiate them from the other groups. (Example: the plants may want to hold their hands out to their sides to represent leaves, the plant-eaters (oryx) may hold their hands on the heads to represent horns, and the predators (lions) may hold their hands up like paws with the claws showing). The predators try to tag the plant-eaters who try to tag the plants. Since predators decompose when they die and become fertilizer, the plants try to tag the predators. Once you are tagged, you turn into whatever tagged you.
After a period of time, stop the game to see how many plants, plant-eaters, and predators are left. Play should resume but should be stopped a few times before the end to determine what has happened and why. After playing a few rounds of the game, select one of the plants to re-enter the game as a human. The rules for the human are different: the human can tag anyone, but no one can tag the human. Each time the human tags someone, that player becomes another human. See how long it takes before all players have become changed into humans.
Discuss the changes and relationships that the game illustrates. Some questions for discussion might include:
- What happens to the plants and plant-eaters if many of the predators have been caught?
- What happens to the plants if many of them have been caught?
- What happens when humans use too much of the food chain? How can we keep that from happening?
- Ask students to record what happened in their science notebooks, including an illustration of the food chain they represented. Talk about the adaptations the various organisms would have to develop in order to survive if one of the species in the food chain became extinct.
