Ecosystems & Food Webs

An ecosystem is every living thing in a place — plants, animals, fungi, and tiny microbes — together with the non-living parts they depend on, like sunlight, water, soil, and air. A pond, a forest, a desert, and even a single rotting log can each be an ecosystem.

Three Roles in Every Ecosystem

• Producers — green plants and algae that make their own food using sunlight.
• Consumers — animals that eat plants, other animals, or both.
• Decomposers — fungi, bacteria, and worms that break down dead material and return nutrients to the soil.

Energy Flows One Way

Energy enters most ecosystems from the sun. Producers capture that energy and store it as food. When a rabbit eats grass, some of that energy moves to the rabbit. When a hawk eats the rabbit, some of it moves to the hawk. At each step, most of the energy is used up — that is why food chains rarely have more than four or five links.

Food Chain vs. Food Web

• A food chain shows one path: grass → rabbit → hawk.
• A food web shows many paths crossing — most animals eat (and are eaten by) more than one species.
• Webs are stronger than chains: if one species disappears, others can still feed something else.

Why Decomposers Matter

Without decomposers, dead plants and animals would pile up and the soil would run out of nutrients. Mushrooms, bacteria, and earthworms quietly recycle everything. They are not at the top of the chain, but the whole ecosystem depends on them.