Weaving the Web

Objective: Students will construct a basic food web and learn about nature's
interdependence.

Materials: A large sheet of blank paper for each group or student, copies of the Student
Worksheet, scissors, tape or glue, markers, pencils, or pens

Background: All creatures rely on other creatures and plants for their food. Food is a link
between all animals, large and small. Small animals eat plants, and then those small animals are
eaten by larger animals. The larger animals are eaten by still larger animals, and so on. These
links through eating comprise what is called a food web.

In real life, however, the connections are not so simple. One animal may eat a variety of foods,
including plants and smaller animals. Other animals may eat plants, animals and decaying
matter. A basic food web is a system of checks and balances, which keeps populations of one
type from dominating others. For example, algae overgrowth is prevented by a variety of
algae-eating insects and fish. Large fish eat small fish, amphibians and reptiles eat small fish,
plants and insects, etc. For an analogy, consider a structure made of children's building
blocks. If the structure is made of many blocks at each level, it is less likely to collapse when
one block is removed. If the structure is made of just a few vertical blocks, the building will
collapse when one block is pulled out.

Procedure:
Divide the students into small groups or have them work individually. Give each student/group
a large blank sheet of paper. Explain that each will receive a worksheet with pictures of
animals that are common to aquatic habitats, such as lakes, wetlands, rivers and ponds. They
will construct a food web, based on their knowledge of what types of creatures eat others.
Remind them to try to make their web as strong as possible by building as large a number of
relationships between organisms as possible.

Give each group or student the Student Worksheet to cut out.

Ask them to arrange the pictures in a realistic order on the blank sheet of paper. Have them
arrange the web starting with the plants at the bottom, building the next level with herbivores,
then smaller predators and finally larger predators.

After they decide where everything should be placed, have them tape or glue each picture
onto the larger sheet.

Ask them to draw arrows connecting each organism to the food it eats. For example, arrows
would go from the algae to the mosquitos, and from the algae to the fish. Some arrows may
skip between levels of the food web: for example grasshoppers can be eaten by fish and by
snakes.

Have each group share their food web with the whole group. Have them compare the
differences between each and converse about the reasons for the differences.

If time permits, have group/student decorate their food web paper with scenes depicting
where each organism resides.

Click here for a predator/prey table.

Extensions:
To further illustrate nature's interdependence, play "Hooks and Ladders" from Aquatic Project
WILD. This high energy game demonstrates the life cycle of a Pacific salmon. It will also
reinforce the food web activity above.

Divide class into small groups. Assign each group a specific level of a food web (i.e., group A
are insects, group B are fish, etc.). Children can design props and costumes if time permits.
Have the group discuss what they will eat and what eats them. Bring the entire class back
together and have each group "capture" another group, depending on whether they are eating
or being eaten: example, plant group will be captured by the insect group. After each group
has been captured at least once, play round two where each large group captures another
group (i.e., the plants and insects group is captured by the fish and amphibian group). Note: the
groups may differ each time the game is played due to different paring: example, the fish
group may be eaten by the bird group, etc.). Play continues until the food web is complete -
predators have eaten all the other groups, or until the food web is unbalanced and the
predators are starving.

Vocabulary Glossary:
Interdependence: when different things need eachother to survive