Ecological Pyramids

Ecological pyramids are graphical representations of the number of individuals in different nutritional levels. For example, the plant-insect-bird-hawk food chain can be represented as an ecological pyramid (see Figure 1). Plants absorb energy from the sun, the insects eat the plants, the birds eat the insects, and the hawks eat the birds. Hence, the energy of the sun has been transferred from the sun to the tissues of the hawk. Since the number of individuals in each level usually decreases, the resulting diagram looks like a pyramid.

The number of individuals does not always decrease. Therefore, the diagram for some ecological "pyramids" is not always in the shape of a true pyramid. If the first level of Figure 1 was "trees" instead of plants, the "pyramid" would not be a pyramid because the number of trees is less than the number of insects. Ecological pyramids represent the basic laws of energy. The first law of thermodynamics states that the amount of energy remains constant. The second law states that "useful energy decreases at each conversion." Therefore, ecological pyramids represent the transfer of energy from one level to another. The laws of thermodynamics ensure the pyramid of energy to be a true pyramid.(Eblen, 1994, p. 161)


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