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.
More to read
20.1 Energy Flow through Ecosystems
A food chain is one straight line of eating, but real nature is messier. A rabbit eats grass and clover, a fox eats rabbits and mice, and an owl eats mice too. When you draw every chain in a habitat on one page, the lines cross into a web.
Webs are more honest than chains because most animals eat more than one thing. Arrows show the flow of energy, pointing from the meal toward the eater. Reading a web means tracing those arrows one path at a time.
Learn: Food chains and food webs
Every web has the same cast of roles. Producers such as grass and algae make food from sunlight. Primary consumers eat the producers, secondary consumers eat those plant eaters, and an apex predator at the top has no hunters of its own.
To build a web from data, list each species, then draw arrows from each food to its eater. Check your work by asking if every animal has at least one arrow pointing in. If a species has none, you have missed its food.
Key points: Matter and energy in food webs
Webs also show how species depend on each other. If rabbits multiply, foxes feast and grass gets nibbled short. If rabbits crash, foxes go hungry and may switch to mice, which then crash too. One change ripples across the whole web.
That is why losing one species can shake many others. Before you predict, find every path that runs through the missing species. Each broken path is a diner that just lost a meal.
Explore more
2 · Watch
به انگلیسیTake 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.