Ecosystem–Structure and Function

In earlier classes, you looked at the abiotic and biotic components of the environment individually — how they affect each other and their surroundings. Here, we look at them together, as an integrated system, and trace how energy actually flows through it.

The interaction between an ecosystem's biotic and abiotic components gives it a physical structure characteristic of that ecosystem type. Identifying and counting the plant and animal species present gives an ecosystem its species composition; the vertical distribution of different species across different layers is called stratification — in a forest, for instance, trees occupy the topmost layer, shrubs the layer below that, and herbs and grasses the bottom layer.

The structure of an ecosystem has two main components. The biotic component includes all living organisms, grouped into three functional categories based on how they obtain food:

• Producers (autotrophs) — organisms that synthesise their own food from inorganic sources, primarily green plants and algae.
• Consumers (heterotrophs) — organisms that feed on other organisms. These include herbivores (primary consumers), carnivores (secondary and tertiary consumers), and omnivores.
• Decomposers (saprotrophs) — organisms such as bacteria and fungi that break down dead organic matter into simpler inorganic substances.

The abiotic component consists of the non-living physical and chemical factors of the environment — sunlight, temperature, rainfall, soil type, pH, and the availability of nutrients.

The function of an ecosystem is driven by four key processes: productivity, decomposition, energy flow, and nutrient cycling. These aren't independent — energy flows through the system in one direction and is eventually lost as heat, while nutrients are recycled and reused, and the ecosystem's structure directly determines how efficiently all of this happens. …