Objective: students learn some of the relationships within a food web
Materials: multiple copies of The Food Web Story
Vocabulary: carnivore, decomposer, detritivore, herbivore, omnivore, primary producer
Comments: When scientists study the structure and functioning of food webs, they use specific terms to describe the relationships between various organisms. Plants are called primary producers because they absorb the energy of sunlight and convert it into food for other organisms. Organisms that eat green plants are called herbivores, and those that eat other animals are called carnivores. Organisms that feed on a great variety of organisms, both plant and animal, are called omnivores. Organisms that rely on dead animals or plant material are called detritivores or decomposers. All of these eat-or-be-eaten relationships make up a food web.
1. Explain the above material and distribute copies of The Food Web Story to students. Ask students to read the story and to place the organisms discussed in the story in the proper categories.
2. As an extension of this activity, have students draw or find pictures of the organisms mentioned in the story and construct a food web.
3. Students draw arrows between organisms that are directly related in the food web (eat or are eaten). Arrows should always point in the direction of energy flow. For example, the flea bites the deer, the flea takes energy from the deer: deer------>flea.
4. Discuss the complete food web and the role each organism plays. Which category of organisms are the most numerous? Which are the heaviest (have the greatest biomass)? What happens if some of the organisms are removed from the ecosystem?
The Food Web Story
Read the story below and match each organism mentioned with one of the four categories below. You may also wish to make a sketch of the entire food web.
On a bright spring day the sun shines onto the forest floor. The warm weather and the moist soil cause plants to sprout. Up through the dead and decomposing leaves (humus) come spring beauties, larkspurs, and other spring flowers. The old oak trees unfold their new leaves, and within a matter of days the leaves begin to produce food by photosynthesis. Mushrooms pop up around rotting logs, and beetle larvae feast on the fungus and decayed wood. Soon the spring warmth triggers the hatching of linden looper caterpillar eggs, and these young caterpillars crawl onto the tender oak leaves and begin feeding. The new tree and understory foliage allow a female deer to eat well; in turn, she provides food to her fawn in the form of milk. The doe rubs her leg against a rough tree because a flea has just bitten her.
Earthworms tunnel through the moist earth, leaving behind little piles of soil in which wildflower seeds will sprout. Aphids find the young oak leaves juicy and nourishing. The aphids stick their needlelike mouth parts into the oak's stems and suck its juice. A bright green tiger beetle walks along sunny forest paths searching for its dinner--linden looper larvae that have fallen off the oak foliage. Elsewhere, spiders spin webs to catch unsuspecting insects like midges and young grasshoppers.
Another inhabitant of the forest, a white-footed mouse, comes out and searches for food--wildflower seeds, mushrooms, acorns, and any caterpillars it finds. Grackles and robins begin courtship and will soon feed caterpillars and earthworms to their young in the nests in the oaks. Linden looper caterpillars have other enemies besides the birds and beetles. A tiny wasp parasite lays her eggs on the caterpillar and the young wasp will feed on it (from the inside out!) until fully grown. As the season progresses, the young birds and mice must be wary of owls and hawks, the deer and fawn wary of the hunter . . . .
Which of the organisms mentioned in the above story are:
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Last Modified 3/19/96