Lesson 4 of 12

🌋 Ecosystems & Food Webs

🎯 Grades 6–8 ⏱ ~35 minutes 🟡 Intermediate

What You'll Learn

The components of an ecosystem: biotic and abiotic factors
Food chains and food webs — energy transfer between organisms
Trophic levels: producers, primary/secondary consumers, decomposers
How removing one species affects an entire ecosystem

🌋 Food Web Simulator

Click "Remove Species" to see what happens when a species disappears. Observe how populations cascade through the food web.

Click a "Remove" button to see the cascade effect.

What Is an Ecosystem?

An ecosystem includes all biotic (living) and abiotic (non-living) factors in an area and their interactions. Biotic: plants, animals, fungi, bacteria. Abiotic: sunlight, water, temperature, soil, air.

Food Chains and Food Webs

A food chain shows one path of energy flow: Grass → Rabbit → Fox. Arrows point from prey to predator (energy flows that direction).

A food web shows all the interconnected food chains in an ecosystem — more realistic because most animals eat multiple things.

Trophic levels: Producers (plants) → Primary consumers (herbivores) → Secondary consumers (carnivores) → Tertiary consumers → Decomposers (fungi, bacteria).

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10% Energy Rule

Only about 10% of energy from one trophic level passes to the next. If grass stores 10,000 calories, rabbits get ~1,000, foxes get ~100. This is why there are always far more plants than herbivores, and more herbivores than carnivores.

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Keystone Species

Some species have a disproportionate impact on their ecosystem. When wolves were reintroduced to Yellowstone, they reduced deer overgrazing, which allowed riverbank vegetation to recover, which stabilized rivers and created habitat for beavers, fish, and birds — a "trophic cascade."

❓ Check Your Understanding

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