Science Fenns K-5Grades K to 5
A food web diagram of grass, grasshoppers, mice, snakes and hawks on a Texas prairie, with one link crossed out.

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When a Food Web Changes

Predict the ripple.

Lesson 36 of 41

Try this first

Before we start

Today’s story

When a Food Web Changes

A food web shows who eats what. Energy comes from the Sun. Plants use sunlight to make food. Animals that eat plants get that energy. Animals that eat those animals get some of it too.

Matter cycles too. When plants and animals die, tiny decomposers break them down. The matter goes back to the soil and air. Plants use it again.

If one part changes, others change. Fewer snakes means more mice, and more mice eat more grass. Hawks may go hungry. We can predict these ripples. Here are the steps.

See it

Five steps. Every time.

    Hands on

    Web of Yarn

    25 minutes · Do this with a grown-up nearby

    You need

    • yarn
    • index cards
    • markers
    • a group of 6 to 8
    • tape

    Do this

    1. Write one organism on each card.
    2. Stand in a circle holding a card.
    3. Pass yarn from each eater to what it eats.
    4. Say the link out loud.
    5. One person drops out. Everyone who feels a tug lifts a hand.
    6. Talk about who is affected.
    Write or draw: A drawing of the web with a note on who felt the tug when someone dropped out.

    Watch for: Even far links feel a pull. Removing one organism changes many.

    Safety: Move slowly and keep the yarn loose so no one trips.

    Same every time

    Three rules

    Rule 1Energy flows one way.

    Sun to plants to animals.

    Rule 2Matter cycles.

    Decomposers return it to soil.

    Rule 3Follow the arrows.

    Each arrow points to the eater.

    Grandpa Fenn’s notebook

    Say it like a scientist

    food web
    Many food chains linked together.
    producer
    A living thing that makes its own food, like a plant.
    consumer
    A living thing that eats other living things.
    decomposer
    A living thing that breaks down dead matter.

    Poppy’s quiz

    Six questions

    Tap an answer. Green means right. You will see why.

    Talk about it

    Say it out loud

    • How do you know a change in one animal affects another? What evidence could you find?
    • What happens in a Texas pond or field if the rain stops for a year?
    Did you know

    Reintroducing wolves to Yellowstone changed where elk fed, which let streamside trees grow back, and scientists are still studying all the effects.

    Someone who does this

    A wildlife manager studies how animal numbers change and plans to protect balance.

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