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Definition of an Ecosystem
There are two ways of defining an ecosystem: a physical area populated by groups of organisms that experience similar conditions; and the interaction between organisms and their biotic, meaning other organisms, and abiotic, meaning non-living, components. Various types of relationships can occur within ecosystems: commensalism, in which one species gains and the rest experience no net gain or loss; parasitism, in which one species gains and the other species lose; and amensalism, in which one species loses out, and the others neither gain nor lose.
Simple Ecosystem Models
A simple ecosystem model is often used to visualize the different processes that form an ecosystem. In such a model, an ecosystem is visualized as a series of compartments that represent its various component parts, such as animals, plants, decomposers and soils. These compartments are linked by energy flows and material cycling processes, which often travel in both directions. For instance, plants absorb carbon dioxide from the atmosphere, but carbon dioxide is liberated from plants when they are broken down by decomposers. There are also transfers in and out of the ecosystem. Simple ecosystem models can be drawn for energy transfers, nutrient cycling and for various chemicals as well.
Spatial Scale of an Ecosystem
There is no set scale to which an ecosystem must conform in terrestrial ecosystem ecology. On one hand, the Earth itself may be defined as an ecosystem, with geosphere, atmosphere, and biosphere being its component parts. On the other end of the scale, there are microecosystems, which are tiny ecosystems formed with small spaces and defined by their critical environmental factors, such as high pH or temperature, such that only highly specialized species of microorganisms can exist within them.
Temporal Scale
In terrestrial ecosystems ecology, the temporal scale is also an important factor to consider. Instantaneous effects in an ecosystem include the affect of rain on soil moisture and varying light on photosynthesis. Seasonal factors include seasonal changes in an ecosystem's carbon balance. Succession factors include the importance of the establishment and relative growth rates of plants in explaining ecosystem composition. Species migration factors include the controls on ecosystem nitrogen inputs and productivity. Evolutionary history factors include whether a clone of a particular species is adapted to a current environment. Geological history factors include the controls that regulate the carbon distribution between the land and the ocean.