Ecosystems
An ecosystem is a community of living things (the biotic part) and their non-living surroundings (the abiotic part: soil, water, light, temperature) interacting together. A pond, a forest and the Serengeti plains are all ecosystems. Each organism lives in a habitat and plays a role, or niche, in its community.
Food chains and webs
A food chain shows who eats whom, with arrows pointing in the direction of energy flow. A food web joins many food chains together.
| Level | Organism | Role |
|---|---|---|
| 1 | grass | producer (makes food) |
| 2 | zebra | primary consumer (herbivore) |
| 3 | lion | secondary consumer (carnivore) |
| 4 | decomposers (fungi, bacteria) | break down dead matter and return nutrients |
The producers capture some energy from the Sun. Change how much, and the percentage passed up each level.
Recycling carbon
Carbon is the building block of all living things. It is not used up: it is recycled. Plants take carbon dioxide from the air to make sugar by photosynthesis. Animals get their carbon by eating plants or other animals. Respiration by every living thing, the decay of dead plants and animals by bacteria and fungi, and the burning of wood and fuels all return carbon dioxide to the air.
Keeping nature in balance
Populations stay roughly steady in a healthy ecosystem because predators control prey and food supply limits numbers. People disturb the balance by deforestation, overfishing, pollution and introducing foreign species. Conservation protects ecosystems through national parks, reforestation and sustainable use.
| Human activity | Effect | Better practice |
|---|---|---|
| Cutting trees without replanting | soil erosion, loss of habitat | plant trees, protect forest |
| Overfishing | fish populations collapse | fishing limits, no small mesh nets |
| Dumping waste | pollutes water and soil | recycle and dispose properly |
| Poaching | endangers species | park rangers, community conservation |
Key terms
- Ecosystem
- A community of organisms and their environment.
- Producer
- An organism that makes its own food.
- Consumer
- An organism that eats other organisms.
- Decomposer
- An organism that breaks down dead matter.
- Conservation
- Protecting living things and their habitats.
Summary
- An ecosystem has biotic and abiotic parts.
- Food chains show energy flow from producers to consumers; decomposers recycle nutrients.
- About 10% of energy passes to each next level.
- People can damage the balance of nature or help conserve it.
- Carbon is recycled: photosynthesis takes carbon dioxide from the air; respiration, decay and burning return it.