Smith (1966) emphasized the following general characteristics of most ecosystems:
(1) The ecosystem is a major structural and functional unit of ecology.
(2) The structure of an ecosystem is related to its species diversity; the more complex ecosystems have high species diversity.
(3) The function of the ecosystem is related to energy flow and material cycling through and within the system.
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(4) The relative amount of energy needed to maintain an ecosystem depends on its structure. The more complex the structure, the lesser the energy it needs to maintain itself.
(5) Ecosystems mature by passing from less complex to more complex states. Early stages of such succession have an excess of potential energy and a relatively high energy flow per unit biomass. Later (mature) stages have less energy accumulation and its flow through more diverse components.
(6) Both the environment and the energy fixation in any given ecosystem are limited and cannot be exceeded without causing serious undesirable effects.
(7) Alterations in the environments represent selective pressures upon the population to which it must adjust Organisms which are unable to adjust to the changed environment must needs vanish.
The ecosystem is an integrated unit or zone of variable size, comprising vegetation, fauna, microbes and the environment. Most ecosystems characteristically possess a well-defined soil, climate, flora and fauna (or communities) and have their own potential for adaptation, change and tolerance.
The functioning of any ecosystem involves a series of cycles, e.g., the water cycle and the cycles of various nutrients. These cycles are driven by energy flow, the energy being the solar energy Continuation of life demands a constant exchange and return of nutrients to and from (amongst) the different components of the ecosystem.