Food Chain Game: Build Food Chains and Food Webs

What is a food chain?

A food chain shows how energy passes from one living thing to another as each one eats the next. National Geographic describes it as following the path of energy from producers to the animals that eat them. A simple example from the game's grassland:

Sun → prairie grass → prairie dog → black-footed ferret → coyote

Every food chain starts with energy from the Sun. Plants and algae capture that energy by photosynthesis, storing it in sugar. Animals that eat plants get some of that energy, animals that eat those animals get a little of it, and so on up the chain. The arrows always point from the food to the eater, the direction energy moves.

The parts of a food chain

Each step in a food chain is called a trophic level, from the Greek word for food. The game labels each slot with its level.

The same animal can sit at different levels in different chains. A mouse that eats acorns is a primary consumer; a mouse that eats a caterpillar is a secondary consumer. That is why the game names levels by position in your chain, not by animal.

Producers, consumers and decomposers

Producers make their own food, usually by photosynthesis. On land they are plants; in the ocean, most are phytoplankton, microscopic algae and bacteria that drift near the surface. Without producers there would be no food for anyone else.

Consumers eat other living things. They are grouped by diet, and the game colors each card by diet after you check a chain:

• Herbivores eat only plants or algae: rabbits, deer, sea urchins, caribou.
• Carnivores eat only animals: owls, sharks, rattlesnakes, polar bears.
• Omnivores eat both: red foxes (rabbits and blackberries), robins (caterpillars and berries), coyotes (jackrabbits and cactus fruit).

Decomposers and detritivores, such as fungi, bacteria, earthworms and some beetles, feed on dead material from every level. They recycle nutrients like nitrogen back into the soil so producers can use them again. Without them, dead leaves and animals would pile up and the soil would run out of nutrients.

From food chains to food webs

Real animals rarely eat just one thing. A great horned owl in the game's forest eats mice, rabbits, squirrels, robins and rat snakes. Connect all those chains and you get a food web. The Build a web mode lays out every organism in rows, producers on the bottom, and challenges you to draw every arrow. The forest web has more than 30.

Food webs show why ecosystems are connected. National Geographic notes that removing one species can ripple through the whole web. The game's ocean has a famous example: sea otters eat sea urchins, and urchins eat kelp. Where otters disappear, urchins can multiply and strip kelp forests bare, taking away food and shelter from many other animals. The grassland has another: black-footed ferrets eat almost nothing but prairie dogs, so when prairie dog towns were wiped out, ferrets nearly went extinct. According to the Smithsonian's National Zoo, prairie dogs make up about 90 percent of a wild ferret's diet, and the last 18 wild ferrets were caught in the 1980s to start the breeding program that has since returned them to parts of the Great Plains.

Food chain examples from five ecosystems

Try building each one in the game, then find a different chain that also works. The game counts every working chain you discover. For printable versions, see the ocean food web, desert food web, forest food chain and Arctic food chain diagrams.

The energy pyramid and the 10 percent rule

Energy doesn't pass up a food chain whole. A rabbit uses most of the energy from the grass it eats to hop, grow, keep warm and breathe, and some passes out as waste. Only a small part is stored in its body for a fox to eat. On average, about 10 percent of the energy at one level reaches the next. This is the 10 percent rule.

An energy pyramid draws each level as a layer, widest at the bottom:

The Energy pyramid mode builds this from your own chain. Slide the starting energy or change the percent to see the effect. The 10 percent figure is an average. OpenStax Biology reports a measured transfer of about 14.5 percent between the first two levels in Florida's Silver Springs ecosystem, and notes that warm-blooded animals waste more energy as heat than cold-blooded ones: a caterpillar eating leaves turns about 18 percent of its food energy into body growth, but a squirrel eating acorns may manage as little as 1.6 percent.

The rule explains two things kids often wonder about:

• Why food chains are short. OpenStax notes that after four to six transfers, too little energy is left to support another level. That's why you won't find an animal that hunts orcas.
• Why there are fewer predators than prey. It takes a lot of grass to feed one rabbit, and a lot of rabbits to feed one fox. Top predators need large territories and are always fewer in number.

Why the arrows point the way they do

Kids often draw arrows as "who eats whom" pointing from eater to food, because it feels like the eater is "going to" the food. Scientists draw them the other way because the arrow tracks energy, and energy moves from the food into the eater. A quick check: read each arrow as "is eaten by." Grass → rabbit reads "grass is eaten by rabbit." If it sounds wrong, flip the arrow. The game explains every backward arrow so this sticks.

Using the game at home or in class

• Grades 2 to 3: start in Build a chain with three slots. Ask your child to name the producer each time and say where it gets its energy. Then print the cut-and-paste food chain worksheet.
• Grades 4 to 5: use four or five slots and all five ecosystems. Compare a desert chain with an Arctic chain and talk about how the animals fit their homes. Try the Quiz with the timer off.
• Grades 6 to 8: finish a full web, then use the Energy pyramid with different percentages. Ask what happens to the web if one species disappears. The food web worksheet has an answer key for checking.

Every food chain begins with photosynthesis; see how plants capture that energy in the photosynthesis diagram. For full science programs that cover ecosystems, compare options in our best homeschool science curriculum guide.