Ecosystem, its biotic community and ecosystem services
An ecosystem is all the living things of an area plus the non-living parts they interact with. Producers, consumers and decomposers form its biotic community.
What is an ecosystem?
All the living organisms of an area, together with the non-living physical parts of their environment that they interact with, form an ecosystem. The idea was put forward by A. G. Tansley in 1935; the word comes from the Greek oikos (home) and systema (system). The living parts are the biotic components: plants, animals and microorganisms. The non-living parts are the abiotic components: sunlight, temperature, rain, water, soil and air. Abiotic parts shape what lives where: plants of the coast, the hills and the desert look very different because temperature, soil and moisture differ. Natural ecosystems are either terrestrial (grassland, desert, forest) or aquatic (pond, river, ocean). A garden, aquarium or crop field is a human-made (artificial) ecosystem.
The biotic community: three groups by mode of nutrition
| Group | How it gets food | Examples |
|---|---|---|
| Autotrophs (producers) | Make their own food, mostly by photosynthesis using sunlight; certain bacteria make food by chemosynthesis, without sunlight | Rooted plants on land; phytoplankton (tiny floating plants) and macrophytes (rooted plants of shallow water) in a pond |
| Heterotrophs (consumers) | Eat plants or animals: herbivores eat plants, carnivores eat animals, omnivores eat both | Primary consumer: deer, grasshopper. Secondary: frog, small fish. Tertiary: snake, big fish |
| Saprotrophs (decomposers) | Feed on dead and decaying matter, breaking it into simple substances that go back to the soil, water and air | Some bacteria and fungi |
The pond: an ecosystem you can visit
A pond shows the parts of an ecosystem clearly. Its abiotic parts include the water itself, dissolved oxygen and carbon dioxide, minerals, stones and the soil at the bottom. It has three layers, top, middle and bottom, which differ in temperature, light and oxygen; you feel the cooler water if you dip deeper. Its biotic parts range from microscopic organisms, too small to see with the naked eye, to fish, frogs and water plants. A pond with many kinds of species is a healthy, stable one. Its whole life cycle, from birth and feeding to being eaten and dying, happens within the pond.
Why decomposers matter
Decomposers form the link between the living and the non-living parts of an ecosystem. They break down the complex substances in dead plants and animals into simple forms and return them to the environment, where plants use them again. Without decomposers, dead matter would pile up and the soil would run short of nutrients. This is also why a pond keeps itself clean, while a home aquarium has to be cleaned by hand.
Ecosystem services: what nature gives us free
- Oxygen to breathe, released by plants and algae, which also take in carbon dioxide.
- Food for all living things, made by plants and algae that trap solar energy.
- Water, minerals, wood (for fuel and for building houses) and biomass fuels.
- Climate control by forests, rivers and oceans.
- Natural pest control: predators and parasites keep pests, and so diseases, in check.
- These services are free, so we must use them wisely and leave them for future generations.
A village pond gives water for cattle, fish for food and a home for frogs that eat mosquito larvae: free ecosystem services. A paddy field or a kitchen garden is a human-made ecosystem that still depends on earthworms, bacteria and fungi.
1 marks: “Who first put forward the idea of an ecosystem?” A. G. Tansley, in 1935.
2 marks: “In a pond you find duckweed floating on the water, a frog on a stone and a mould growing on a dead fish. Place each in its nutrition group and say how it gets food.” Duckweed: autotroph (producer), makes food by photosynthesis. Frog: heterotroph (consumer), eats insects and other animals. Mould: saprotroph (decomposer), feeds on dead matter and breaks it down.
3 marks: “What are ecosystem services? Give four examples and say why we must use them wisely.” Free benefits that nature gives us: oxygen, food, water and wood, climate control by forests and oceans, natural pest control. They are limited and must last for future generations.
Bio = life, a-bio = no life. Producers Prepare food, Consumers Consume it, Decomposers Dismantle what is left.