How Many Species Are Required for a Functional Ecosystem

One of the key elements in defining an ecosystem is the spatial extent. The view of an ecosystem taken here is a group of species, both visible above ground and invisible below, which interact vertically and horizontally so that the ecosystem develops endogenous properties. The spatial extent of the ecosystem is that which allows the majority of the ecosystem to experience its endogenous properties. In addition, it is considered to follow that only one ecosystem can exist over one area of land. A consequence of this view is that small scale notions of ecosystems may not conform with this definition. For example, it is often quoted that a small decaying tree trunk is an ecosystem, but the presence of the tree trunk on the ground (following disturbance), the diversity of decomposers on the trunk and the microclimate in which the trunk is found may all accrue from the higher level -top-down — property of the larger scale and entire ecosystem. Therefore, the tree trunk in this example is not a complete ecosystem.

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