Session 3: Introduction to Food Webs

Key Idea

In an ecosystem, matter doesn't stay in one place. It moves. When a sloth eats a leaf, the matter from the leaf moves into the sloth. When a jaguar eats the sloth, that matter moves again into the jaguar.

Scientists use arrows to draw these connections. An arrow pointing from a plant to an animal means matter is transferred into that animal. This movement of matter is critical because it is how organisms get the building blocks and energy they need to survive.

Key Idea

Because matter is transferred by eating, we can link organisms together in a line called a food chain. For example: Plant → Deer → Wolf.

Notice that the chain always starts with a plant. Plants are unique because they don't need to eat other organisms to get matter; they make their own food molecules using air and water. Because they produce the food that supports the whole chain, plants are called producers.

Key Idea

In the real rainforest, relationships are rarely simple straight lines. A jaguar eats sloths, but it also eats deer and monkeys. A sloth is eaten by jaguars, but also by eagles and snakes.

When we overlap all these different food chains, the diagram looks like a tangled spider web. This is called a food web. A food web is a better model than a food chain because it shows the complex, interconnected reality of how matter and energy flow through an entire ecosystem.