Food Webs & Interdependence
Construct and interpret food webs showing the interdependence of organisms in an ecosystem, explaining how a change in one population affects others
What a learner can do afterwards
- Draws a food web from given data with arrows showing energy flow direction
- Predicts how the population of one species would change if another species increased or decreased
- Distinguishes a food web from a food chain and explains why webs are more realistic
- Identifies producers, primary consumers, secondary consumers, and apex predators
1 · Read
You already know that an arrow in a food chain points from food to the animal eating it. In a woodland a hawk may eat both robins and frogs, so one hawk can sit in two chains at once. Most animals eat more than one kind of food and get eaten by more than one predator, so many chains link together into a food web.
Take a meadow: grass feeds both grasshoppers and mice. Grasshoppers get eaten by frogs and by sparrows. Mice get eaten by snakes. Frogs, snakes, and sparrows all get eaten by hawks. Draw every one of those relationships and you get a web, not a single line.
To predict what happens when one population changes, trace the arrows both ways: what did it eat, and what ate it? In a web, the effect can also travel further, changing animals that were never directly connected to the one that changed.
Every living thing in a web has a job, and the jobs have names. A producer makes its own food from sunlight instead of eating anything, which is why plants and algae sit at the base of every chain. A consumer eats something else. Whatever eats the producer is the primary consumer, whatever eats that one is the secondary consumer, and the chain carries on from there. At the top sits the apex predator, the animal with nothing in the web hunting it.
A food web links many food chains together, so a change in one population can ripple through several others, not just its direct neighbors.
2 · Watch
Take it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
24 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.