The fundamental energy source for most of the ecosystems is radiant energy taken from the sun. The ecosystem's self-sustaining organisms use the energy from sunlight to sustain themselves; an example would be green vegetation. Organisms are capable of photosynthesis, meaning they use sunlight energy to convert carbon dioxide into energy rich carbohydrates. Autotrophs (organisms that can change inorganic substances, like carbon dioxide, into nutritional organic substances) use the carbohydrates to produce organic compounds that help maintain life processes of the organisms.
Autotrophs generate organic matter and heterotrophs consume the organic matter because they cannot make their own food. Animals and fungi are examples of heterotrophs; organisms that use and ultimately decompose complex organic matter. The autotrophs and heterotrophs combine together to form the various feeding levels in the ecosystem. At the first level, the organisms make their own food; the next level comprises organisms that cannot make their own food -- the primary consumers, then come the secondary consumers who feed on the primary consumers. The food chain is built up through various consumer levels.
Nutrients in an ecosystem are the chemical elements necessary for living organisms. The energy flowing through the ecosystem drives movement of these essential nutrients. Biogeochemical cycles keep the nutrients continually cycling through the ecosystem. Examples of these cycles include the oxygen cycle, carbon cycle and water cycle. Decomposers play a major role in each cycle by returning the nutrients to soil, water or air. Once returned to the source, the nutrients are again used by the biotic organisms of the ecosystem.
Ecosystem development is defined as the orderly replacement of one ecosystem by another. However, human interference in ecosystem development is widespread. For example, farming may be considered the deliberate maintenance of an immature ecosystem; a productive yet relatively unstable ecosystem. Ideally, good management of existing ecosystems should be a compromise between young and mature ecosystems for optimal food production. Short term food production only hinders efficient energy use and will lead to an imbalance in nutrients, increased plant diseases and increased pollutants.