Lesson 7 of 14
Pull one link and the rest move
Show on a big screenNets take most fish from a pond. Then the tadpoles grow in number.
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Step 1 of 4
- Algae feed tadpoles. Tadpoles feed fish. Fish feed herons.
- Take the fish away. Hold them at 0.
- Fewer fish means more tadpoles survive.
- Fewer fish also means herons have less food.
The rule
A simple chain has one food and one eater at each step.
A kind falls when its numbers get smaller. It rises when they get bigger.
In a simple chain, when one kind falls, what it eats rises. What eats it falls. Fewer eaters mean more food is left. Less food means fewer eaters.
An ecosystem is in balance when its numbers stay steady. Natural or human causes can break the balance.
In India, many frogs were caught to sell in other countries. Frogs eat pests, insects that harm crops. Fewer frogs meant more pests.
Watch out!
A web is not a chain. An eater with other foods may not fall.
Try the lab to finish this lesson.