Thursday, October 31, 2013

Ecological Pyramids

Ecological Pyramids
The graphical representation of structure and function of tropic levels of an ecosystem, starting with producers at the top and each successive tropic level forming the apex is known as an ecological pyramid.
In a food chain starting from the producers to the consumers, there is a regular decrease in the properties (i.e., energy, biomass and the number of organisms) Since some energy is lost in each tropic level, it becomes progressively smaller at the top.

Ecological pyramids are of three types:
  1. Pyramid of Numbers
  2. Pyramids of Energy and
  3. Pyramid of Biomass
 Pyramid of Numbers It represents the number of individual organisms present in each tropic level.
Ex: A grassland Ecosystem
Producers are grass (small in size and large in number. Hence they occupy the first tropic level
The primary consumers are rats occupying the second tropic level. It is worthwhile to note that rats are less in number than grass.
Secondary consumers are snakes which occupy the third tropic level and they are lesser in number than rats.
Tertiary consumers are Eagles that occupy the next tropic level. This is the last tropic level where the number and size of the tropic level is the least as shown in the diagram.

 Pyramid of Energy It represents the amount of energy present in each tropic level. The rate of energy flow and the productivity at each successive tropic level is shown in the figure below.
At every successive tropic level, there is a heavy loss of energy (almost 90%) in the form of heat. Thus, at each tropic level only 10% is transferred. Hence there is a sharp decrease in energy at each and every successive tropic level as we move from producers to top consumers (carnivores).
Pyramid of  energy is depicted in the figure below.


 Pyramid of Biomass: It represents the total amount of biomass (mass or weight of biological material) present in each tropic level. Considering the example of a forest ecosystem, there is a steady decrease in the biomass from the lower tropic level to the higher tropic level. The producers (trees) contribute a major amount of the biomass. The next tropic level are the herbivores (insects and birds) and carnivores (snakes, foxes, etc). The top of the tropic level consists of very few tertiary consumers (Ex: Lions and Tigers) whose biomass is very low. The pyramid of biomass is shown below

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