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ELI5 Yahaaa

Energy passed along

Who Eats Whom?

A food chain traces sunlight as it moves from plants through animals, losing most of itself at each step.

1 Sunlight2 Plantscapture it3 Animals eatplants4 Predatorseat thoseanimals
Everything on the chain is really eating sunlight.

  1. Step 1 of 5

    It starts with plants, always.

    Plants Make food from lightAnimals Can only eat whatalready exists

    Only plants and algae can turn sunlight into food. Every animal, however fierce, is ultimately living on what a plant captured.

  2. Step 2 of 5

    Eating passes the energy along.

    Grass Passed up thechainEnergy moves one direction only

    A rabbit eating grass takes some of the energy the grass captured. A fox eating the rabbit takes a share of that.

  3. Step 3 of 5

    Most of it is lost at every step.

    Plantsenergy capturedPlant eatersabout 10%Predatorsabout 1%

    Roughly 90 percent is spent on moving, staying warm and living. Only about a tenth is available to whatever eats next.

  4. Step 4 of 5

    Which is why chains are short.

    Top predator — very fewlittle energyleft up herePredators — someliving on1%Plant eaters — manyliving on 10%Plants — enormousnumbersthe wholesupply

    After four or five links there is essentially nothing left. That is why there are no predators that hunt lions — the energy has run out.

  5. Step 5 of 5

    Decomposers close the loop.

    Plants grow Animals eat Everything dies Decomposersreturn thenutrientsA loop

    Fungi and bacteria break down everything that dies, returning nutrients to the soil for plants. Without them the chain would stall.

    Real ecosystems are webs, not chains. Most animals eat several things and are eaten by several others.

The short version

Food chains pass sunlight from plants upward, losing about 90 percent at each step, which is why they are short.

Try it yourself

Trace your dinner backwards to a plant, and then to sunlight. Every meal gets there within a few steps.

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