The essentials
An ecosystem is a functional unit of nature where living organisms interact among themselves and with their surrounding physical environment. Its size ranges from a small pond to a large forest or sea. Many ecologists regard the entire biosphere as a global ecosystem. Ecosystems are broadly terrestrial (forest, grassland, desert) or aquatic (pond, lake, wetland, river, estuary). Crop fields and aquaria are man-made ecosystems.
Structure: An ecosystem has biotic components (producers, consumers, decomposers) and abiotic components (light, temperature, water, soil, inorganic nutrients). The identification and enumeration of plant and animal species gives its species composition. Stratification is the vertical distribution of different species occupying different levels; in a forest, trees occupy the top vertical layer, shrubs the second, and herbs and grasses the bottom layers.
A pond as an example: A pond is a shallow, fairly self-sustaining water body that shows all basic components:
- Abiotic: water with dissolved inorganic and organic substances and the soil deposit at the bottom; solar input, temperature cycle, day length.
- Producers: phytoplankton, some algae, and floating, submerged and marginal plants.
- Consumers: zooplankton, free-swimming and bottom-dwelling animals.
- Decomposers: fungi, bacteria and flagellates, especially abundant at the bottom.
Functions: All ecosystems perform four basic functions: productivity, decomposition, energy flow and nutrient cycling. In a pond, producers convert inorganic material into organic material using the sun's radiant energy, heterotrophs consume autotrophs, dead organic matter is decomposed to release minerals for reuse, and energy flows in one direction towards higher trophic levels while some is lost as heat to the environment.
Common mistakes
- Decomposers are part of the biotic component, not the abiotic component.
- Energy flows in one direction; it is nutrients, not energy, that cycle.