Wednesday, April 6, 2011

Food chain


The food chain may be defined as the transfer of energy from its source in green plants through a series of ‘higher’ organisms, the animals inhabiting a given system. The energy gets transferred through the food chain by the process of grazing or predation. We know that the plants have been the original source of the food energy. Therefore, they have been termed as the producers, or autotrophs. Animals feeding directly upon the plants are known as herbivores, or primary consumers, while predators are termed secondary, tertiary, etc. consumers, depending upon the actual source of their food. A well-managed fish pond will serve to illustrate a typical food chain. In this system the plants, generally phytoplankton, have been fed upon by the primary consumers, the zooplankton, in turn; serve as a food source for bloodworms, or chironomids, which could occupy the position of secondary consumers. The bloodworms have been the food source of small fish like bluegills and are, in turn, preyed upon by bass.
Biological method of zonation: As sunlight has been such an important factor in the productivity of these systems, it has been customary to divide both marine and freshwater systems into definite zones on the basis of the depth of sunlight penetration. This has been primarily a biological method of zonation. The upper zone of sunlight penetration is known as the euphotic zone. Beneath this is a zone of perpetual darkness, the dysphotic zone, which is extending from the bottom of the euphotic zone to the bottom. The bottom sediment underlying the dysphotic zone is known as the benthic zone or the regeneration zone. According to this type of classification, shallow lakes, streams and rivers would not behaving a dysphotic zone, as they would be shallow enough to allow for sunlight penetration down to the benthic zone. In addition, the position of both euphotic and dysphotic zones in deep systems generally shifts with the environmental conditions.
Lotic environment: The lotic environment is consisting of all inland waters in which the entire water body continually moves in a definite direction. Thus rivers, streams, and brooks are regarded to be lotic environments.
Lentic environment: The lentic environment has been including all inland waters in which the water has been not continually flowing in a definite direction. The water in these systems has been essentially standing, although some water motion may take place because of wind driven waves and/or in the vicinity of inlets and outlets.





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