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Tuesday, December 30, 2008

6)What are ecological pyramids? Describe the different types of ecological pyramids.

An ecological pyramid is a graphical representation designed to show the biomass or productivity at each trophic level in a ecosystem.
*Each stage in a food chain is known as a trophic level.


The picture above shows an ecological pyramid

There are two types of ecological pyramid, the Pyramid of biomass and the Pyramid of energy(pyramid of productivity).

Pyramid of biomass
An ecological pyramid of biomass shows the relationship between biomass and trophic level. It is constructed based on the dry mass of organisms in each trophic level at any one time. Lets take this food chain as an example.
Grass-->Rabbit-->Snake-->Hawk
All the grass together have a larger biomass than the rabbits, all the rabbits together have a larger biomass than the snake, all the snakes together have a larger biomass than the hawks. Hence, the pyramid of biomass for this food chain will be broad at base and narrow towards the top.

Pyramid of energy
An ecological pyramid of energy shows the production or turnover of biomass at each trophic level. It is constructed base on the total energy level in each trophic level over a certain period of time,for e.g, 1 year.
More and more energy is lost as it goes down a food chain.Almost 90% of the energy is lost when it is transferred from one trophic level to another. The total energy level is the highest at the first trophic level and lowest at the last trophic level. Hence, the pyramid of energy is always broad at base and narrow towards the top.

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