Ecosystem

An ecosystem is a community of living organisms interacting with each other and their non-living environment.

Definition

An ecosystem is a community of living organisms (biotic components) interacting with each other and with their non-living physical environment (abiotic components) as a functional system. The biotic components include all plants, animals, fungi, and microorganisms in the area. The abiotic components include sunlight, temperature, rainfall, soil, water, and air. Energy flows through an ecosystem via food chains and food webs, while nutrients are continuously recycled.

Key Characteristics

Contains both biotic (living) and abiotic (non-living) components that interact
Energy flows through the ecosystem from producers → consumers → decomposers
Nutrients (carbon, nitrogen, water) are cycled and recycled within the ecosystem
Ecosystems have producers (plants), consumers (animals), and decomposers (fungi, bacteria)
Ecosystems vary enormously in size — from a pond to the entire Amazon rainforest
Biodiversity (variety of species) contributes to ecosystem stability and resilience

Real-World Analogy

An ecosystem is like a city. The plants are the city's farms and power stations (producers of food and energy). Herbivores are the factory workers consuming raw materials. Carnivores are managers. Decomposers are the recycling and waste-management service, breaking everything down and returning nutrients to the ground for use again. Remove any one group and the whole city begins to fail.

Note

An ecosystem is a system made up of all the living organisms in an area together with the non-living environment they inhabit. Energy enters through photosynthesis in producers and flows through food chains to consumers and decomposers. Nutrients are recycled within the system. Healthy ecosystems with high biodiversity are more resilient to disturbance.

Worked Examples

A woodland ecosystem

In a temperate woodland, oak trees (producers) are eaten by caterpillars (primary consumers), which are eaten by blue tits (secondary consumers), which are eaten by sparrowhawks (tertiary consumers). When any organism dies, fungi and bacteria (decomposers) break down the remains, returning minerals to the soil so trees can absorb them again.

Human impact on ecosystems

Deforestation removes producers from a forest ecosystem, reducing food and habitat for consumers. Without plant roots, soil erodes. Fewer trees mean less CO₂ absorbed, contributing to climate change. The loss of one species can trigger a cascade of effects throughout the whole ecosystem — a phenomenon called a trophic cascade.

Practice Problems

What is the difference between a biotic and an abiotic component of an ecosystem? Give two examples of each.

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Biotic components are living: e.g. plants, animals, fungi, bacteria. Abiotic components are non-living: e.g. sunlight, temperature, rainfall, soil type.

Explain the role of decomposers in an ecosystem.

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Decomposers (fungi and bacteria) break down dead organic matter — plant and animal remains — into simpler inorganic nutrients. These nutrients are returned to the soil, where they can be absorbed again by plants, completing the nutrient cycle.

A disease kills all the grass in a grassland ecosystem. Predict two effects this would have on other organisms in the ecosystem.

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Any two: herbivores (rabbits, gazelle) would lose their food source and populations would decline; carnivores that eat herbivores would also decline due to reduced prey; decomposers might initially increase as dead grass provides organic matter; soil may erode without grass roots holding it.

Why do ecosystems with higher biodiversity tend to be more stable than those with low biodiversity?

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With more species, there are alternative food sources and pathways in the food web. If one species declines, others can fill its role, preventing total collapse. Low-biodiversity ecosystems (e.g. monoculture farms) are fragile — one pest or disease can devastate the entire system.