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- 1. An ecosystem consists of a set of living organisms and their physical and chemical environment.
- 2. By the structure of an ecosystem we mean the arrangement of its physical components, e.g. plants, animals, soils, climate.
- 3. By the function of an ecosystem we mean how it works, how its various components are linked together into a single integrated unit.
- 4. Ecosystems can be identified by using vegetation, e.g. tropical rain forest, Alpine pasture, salt marsh.
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 Ecosystem Structure
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- 1. Biomass is the total amount of living material in an ecosystem at any given moment.
- 2. It can be measured as a (dry) weight of tissue per unit area.
- 3. Biomass is distributed unevenly: (i) within individual ecosystems, as indicated by the above-ground to below-ground biomass ratio, (ii) between different ecosystems. 4. In many ecosystems the dead organic matter (DOM) greatly exceeds the luring biomass in volume or weight.
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 Ecosystem Processes (function)
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- 1. Energy flow involves: (i) the absorption of light energy by green plants; (ii) the passage of this energy through the ecosystem as food by means of animal consumption; (iii) its final loss from the ecosystem as heat.
- 2. Energy fixation or light fixation by plants is called photosynthesis or primary production.
- 3. The rate of energy fixation or production is referred to as productivity.
- 4. The simple linear flow of energy in the ecosystem from plants to animals to decomposers is called a food chain.
- 5. Each stage in the chain where energy or food is exchanged is known as a trophic or feeding level.
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- 6. More realistically, energy flows through an ecosystem in the form of a more complicated food web.
- 7. There are seldom more than five or six trophic levels in a food chain or web because respiratory heat is lost at each trophic exchange.
- 8. Humans modify energy flow within ecosystems by making the production or the yield of desirable products as high as possible.
- 9. Biological or nutrient cycling refers to the circulation of chemical elements from the environment to organisms and back again to the environment.
- 10. The reserve of nutrients in ecosystems can be easily increased or decreased by human activity.
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Introduction