Change in Communities Over Time

Change in Communities Over Time - communities lack...

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Change in Communities Over Time Secondary succession occurs when an environment has been disturbed, such as by fire, geological activity, or human intervention (farming or deforestation in most cases). This form of succession often begins in an abandoned field with soil layers already in place. Compared to primary succession, which must take long periods of time to build or accumulate soil, secondary succession occurs rapidly. The herbaceous pioneering plants give way to pines, which in turn may give way to a hardwood deciduous forest (in the classical old field succession models developed in the eastern deciduous forest biome). Early researchers assumed climax communities were determined for each environment. Today we recognize the outcome of competition among whatever species are present as establishing the climax community. Climax communities tend to be more stable than successional communities. Early stages of succession show the most growth and are most productive. Pioneer
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Unformatted text preview: communities lack diversity, make poor use of inputs, and lose heat and nutrients. As succession proceeds, species variety increases and nutrients are recycled more. Climax communities make fuller use of inputs and maintain themselves, thus, they are more stable. Human activity (such as clearing a climax forest community to establish a farm field consisting of a cultivated pioneering species, say corn or wheat) replaces climax communities with simpler communities. Communities are composed of species that evolve, so the community must also evolve. Comparing marine communities of 500 million years ago with modern communities shows modern communities composed of quite different organisms.Modern communities also tend to be more complex, although this may be a reflection of the nature of the fossil record as well as differences between biological and fossil species....
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