Ecosystems and Food Webs

An ECOSYSTEM is a group of living things (plants, animals, fungi, bacteria) AND the nonliving things (water, soil, air) that share a place. Ecosystems are everywhere — in ponds, forests, deserts, even your backyard. Today you will learn the rules that keep ecosystems ALIVE.

Every living thing has a JOB:\n\n**PRODUCERS** — make their own food using sunlight. Plants, algae.\n\n**CONSUMERS** — eat other things:\n- Herbivores eat plants (rabbits, deer)\n- Carnivores eat meat (lions, hawks)\n- Omnivores eat both (bears, humans)\n\n**DECOMPOSERS** — break down dead things into soil. Bacteria, fungi, earthworms.\n\nEcosystems need all 3 to work.

A FOOD CHAIN shows who eats what, in order:\n\nSun → Grass → Rabbit → Fox\n\nEnergy flows from sun to plants to herbivores to carnivores. Each step is a "LINK" in the chain. Break a link and the whole chain is in trouble.

In real nature, it is rarely just one food chain. Many chains OVERLAP in a FOOD WEB.\n\nExample in a meadow:\n- Grass is eaten by rabbits AND grasshoppers AND deer\n- Rabbits are eaten by hawks AND foxes\n- Grasshoppers are eaten by birds AND frogs\n\nWeb = more connections = more resilient ecosystem.

Things that can HURT an ecosystem:\n\n- **Losing a predator** — prey overgrow, eat all the plants, collapse\n- **Losing a producer** — everything that depended on it starves\n- **Invasive species** — new animals upset the balance\n- **Pollution** — poisons soil, water, and air\n- **Habitat loss** — forests cut down, wetlands drained\n\nEvery species has a role. Lose one and the web weakens.

In 1995, wolves were returned to Yellowstone National Park after being gone for 70 years. Amazing things happened:\n\n- Wolves hunted elk → elk populations dropped\n- Fewer elk = more grasses and trees grew back\n- More trees = beavers built dams\n- Dams created wetlands for frogs, fish, birds\n- Rivers even CHANGED COURSE because of the new plants\n\nOne missing species had changed EVERYTHING. Bringing it back healed the whole ecosystem.