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The following points highlight the three main types of ecological pyramids. The types are: 1. Pyramid of Numbers 2. Pyramid of Energy 3. Pyramid of Biomass.
Type # 1. Pyramid of Numbers:
In a food chain the members at the successive higher levels are smaller in number. For example in a pond the lowest trophic level is represented by algae and diatoms, which are largest in number.
The second trophic level is represented by herbivorous zooplankton, such as copepods, Ranatra etc., which are less abundant in number. While the third and fourth trophic levels are occupied by smaller and larger fish, respectively. There is a considerable reduction in the number of individuals from the base to the top of the pyramid. Another example may be quoted of a forest.
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In a forest the small herbivorous insects are more abundant than the insectivorous birds, similarly the preying birds, such as hawks are fewer than insectivorous birds.
Type # 2. Pyramid of Energy:
The amount of energy and matter transferred through food to successive higher levels become less and less. Greater amount of energy is available at the producer level than at the primary consumer level (herbivores). The energy production of the primary consumer is greater than that of the secondary consumers (i.e., primary carnivores) which form next link in the energy chain.
The energy at the tertiary consumer level (secondary carnivores) is produced in minimum amount. The actual fractions or percentages of energy from food at one level converted to energy from food at the next level may be more than 10 per cent or less than 10 per cent. This general pattern forms an energy pyramid, because each successive trophic level has less energy available to it.
Type # 3. Pyramid of Biomass:
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The biomass is defined as the total weight of dry matter (dry weight) present in the ecosystem at any one time. The biomass can be measured graphically. This graph represents the shape of a pyramid which is known as pyramid of biomass. This pyramid shows the total mass of organisms and gives a rough picture of the overall effect of food chain relationships for the ecological group as a whole.
In studies of energy flow, the number of organisms at any trophic level depends upon the availability of organisms which serve as food at the lower level. For example the number of particular herbivorous insect would increase if more plant food was available to them.
In this way, a large amount of food would be available not only to its prey, such as the frog but also to other animals such as a bird which feeds on that insect as a second choice which leads to an increase in their number.
With the result of the increased predation the number of herbivorous insects is decreased and this in turn leads to a reduction in the number of their predators. Thus the balance of nature is maintained by the availability of food.
