Ecosystems
Producers, consumers and decomposers, one-way energy flow and recycled nutrients
Scope: The ecosystem as one working unit of living and non-living things. Larger divisions of the Earth are covered in the notes on biosphere and biomes.
In one minute
An ecosystem is a community of living things together with the non-living surroundings they interact with, working as one unit. A pond, a forest patch and a farm are all ecosystems.
Energy flows through it in one direction, while nutrients are used again and again. Exams ask for its parts, how energy moves and why pollution upsets its balance.
Exam focus
- Frequency: Rarely asked
- Usually asked as: Short answer (4 to 6 marks)
Legal provision
No Indian Act defines an ecosystem. Two provisions still use the idea.
- Section 2(b), Biological Diversity Act, 2002: biological diversity means the variability among living organisms from all sources and the ecological complexes of which they are part, including diversity "of eco-systems".
- Section 2(a), Environment (Protection) Act, 1986: environment includes the inter-relationship among water, air, land and living beings, which is what an ecosystem is made of.
Meaning and definition
An ecosystem is a community of interacting organisms together with their physical surroundings, functioning as a unit. The British ecologist A.G. Tansley introduced the word in 1935.
Ecosystems come in three broad kinds. Terrestrial ones are on land, such as forests and grasslands. Aquatic ones are in water, such as lakes, rivers and oceans. Artificial ones are made by people, such as farms, reservoirs and city parks.
- Ecosystem
- Biotic (living) partProducers make food. Consumers eat others. Decomposers break down dead matter.
- Abiotic (non-living) partSunlight, water, air, soil and temperature.
Detailed explanation
Step 1: the three living roles
Producers (green plants and algae) make food from sunlight by photosynthesis. Consumers (herbivores, carnivores and omnivores) feed on other organisms. Decomposers (fungi and bacteria) break down dead matter and return nutrients to the soil and water.
Example. In a paddy field in the Godavari delta, the rice plant is the producer. A grasshopper and a frog are consumers. Fungi in the soil are decomposers.
Step 2: energy flows one way
Energy enters from the Sun, passes from producers to consumers, and is lost as heat at each step. It never returns to the start. This is why an ecosystem needs sunlight all the time.
Example. Grass stores solar energy. A deer eats the grass and a tiger eats the deer. Much of the energy is lost as heat at each step, so far less reaches the tiger than the grass first held.
Step 3: nutrients are recycled
Carbon, nitrogen and phosphorus move in cycles. Plants take them up, animals eat the plants, and decomposers return them to the soil and air. Energy is one-way, but nutrients go round.
Step 4: food chains and food webs
A food chain is a single line of feeding, such as grass, deer, tiger. A food web joins many chains, because most animals eat more than one thing. Real ecosystems are webs.
Step 5: balance and its loss
A healthy ecosystem tends to keep itself steady, a property called homeostasis. It can absorb small shocks. Heavy pollution, such as untreated effluent into a lake, can overwhelm it. The lake then loses fish and plants and may not recover.
Step 6: why the law protects whole ecosystems
Protecting one species is not enough if its ecosystem is destroyed. The law therefore protects habitats and whole systems, for example through sanctuaries, national parks and the rules on biodiversity. The Biological Diversity Act, 2002 counts diversity of ecosystems as part of biological diversity.
Don't confuse: ecosystem, habitat and biome
| Point | Ecosystem | Habitat | Biome |
|---|---|---|---|
| Meaning | Living and non-living things working as a unit | The place where one kind of organism lives | A large region defined by its climate and typical life |
| Size | Small or large, such as a pond or a forest | Usually small and specific | Spans continents |
Inside the concept. The Hussain Sagar lake in Hyderabad, with its water, fish, birds, plants and microbes, is one ecosystem.
Just outside it. The hollow of a tree where an owl nests is the owl's habitat. It is a place, not a whole working system.
Common mistakes
- Saying energy is recycled. Energy flows one way and is lost as heat; nutrients are recycled.
- Calling a food chain and a food web the same. A web joins many chains.
- Leaving out decomposers when listing the living roles.
- Mixing up ecosystem and habitat.
Leading case laws
No Indian case turns on the meaning of ecosystem. Courts apply the idea in cases on forests, wetlands and rivers, covered in the notes on those topics.
How to write this answer in the exam
5-mark answer
- Definition of ecosystem.
- Living and non-living parts.
- Producers, consumers, decomposers.
- Energy flow and nutrient cycling.
10-mark answer
- Definition and origin of the word.
- Kinds: terrestrial, aquatic, artificial.
- Biotic and abiotic parts, with the three roles.
- Energy flow, food chain and food web.
- Nutrient cycling and balance.
- Effect of pollution on balance.
- Legal link: section 2(b) of the 2002 Act.
Key points to remember
- Ecosystem: living community plus non-living surroundings as one unit.
- Roles: producers, consumers, decomposers.
- Energy flow is one-way; nutrient cycling is circular.
- A food web joins many food chains.
- Homeostasis: the ecosystem's tendency to stay balanced.
- Section 2(b) of the 2002 Act includes diversity of ecosystems.
Quick self-test
1. Name the three living roles in an ecosystem.
Producers, consumers and decomposers.
2. Which moves in a circle, energy or nutrients?
Nutrients. Energy flows one way and is lost as heat.
3. How is a food web different from a food chain?
A chain is one line of feeding. A web joins many chains.