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Ecological Pyramid
Jul 27, 2015

An ecological pyramid (also trophic pyramid, energy pyramid, or sometimes food pyramid) is a graphical representation designed to show the biomass or bio productivity at each trophic level in a given ecosystem. Biomass is the amount of living or organic matter present in an organism. Biomass pyramids show how much biomass is present in the organisms at each trophic level, while productivity pyramids show the production or turnover in biomass. Ecological pyramids begin with producers on the bottom (such as plants) and proceed through the various trophic levels (such as herbivores that eat plants, then carnivores that eat herbivores, then carnivores that eat those carnivores, and so on). The highest level is the top of the chain. An ecological pyramid of biomass shows the relationship between biomass and trophic level by quantifying the biomass present at each trophic level of an ecological community at a particular time. It is a graphical representation of biomass (total amount of living or organic matter in an ecosystem) present in unit area in different tropic levels. Typical units are grams per meter2, or calories per meter2.

General concepts

Energy flows through the food chain in a predictable way, entering at the base of the food chain, by photosynthesis in primary producers, and then moving up the food chain to higher trophic levels.  Because the transfer of energy from one trophic level to the next is inefficient, there is less energy entering higher trophic levels.   

It may also be useful and productive to examine how the number and biomass of organisms vary across trophic levels.  Both the number and biomass of organisms at each trophic level should be influenced by the amount of energy entering that trophic level. When there is a direct correlation between energy, numbers, and biomass then biomass pyramids and numbers pyramids will result.  However, the relationship between energy, biomass, and number can be complicated by the growth form and size of organisms and ecological relationships occurring among trophic levels.  Thus, it is possible, and common that biomass pyramids and numbers pyramids do not look like pyramids at all

Types

There are 3 types of ecological pyramids as described as follows: 

  • Pyramid of  energy 

  • Pyramid of numbers and

  • Pyramid of biomass.

Pyramid of Energy

The pyramid of energy or the energy pyramid describes the overall nature of the ecosystem. During the flow of energy from organism to other, there is considerable loss of energy in the form of heat. The primary producers like the autotrophs there is more amount of energy available. The least energy is available in the tertiary consumers. Thus, shorter food chain has more amount of energy available even at the highest trophic level. 

  • The energy pyramid always upright and vertical. 

  • This pyramid shows the flow of energy at different trophic levels. 

  • It depicts the energy is minimum as the highest trophic level and is maximum at the lowest trophic level. 

  • At each trophic level, there is successive loss of energy in the form of heat and respiration, etc. 


Pyramid of Numbers

The pyramid of numbers depicts the relationship in terms of the number of producers, herbivores and the carnivores at their successive trophic levels. There is a decrease in the number of individuals from the lower to the higher trophic levels. The number pyramid varies from ecosystem to ecosystem. There are three of pyramid of numbers:

  • Upright pyramid of number 

  • Partly upright pyramid of number and

  • Inverted pyramid of number.


Upright Pyramid of Number 

This type of pyramid number is found in the aquatic and grassland ecosystem, in these ecosystems there are numerous small autotrophs which support lesser herbivores which in turn support smaller number of carnivores and hence this pyramid is upright. 



Partly Upright pyramid of Number 

It is seen in the forest ecosystem where the number of producers are lesser in number and support a greater number of herbivores and which in turn support a fewer number of carnivores. 



Inverted Pyramid of Number 

This type of ecological pyramid is seen in parasitic food chain where one primary producer supports numerous parasites which support more hyperparasites. 



 

Pyramid of Biomass

The pyramid of biomass is more fundamental, they represent the quantitative relationships of the standing crops. In this pyramid there is a gradual decrease in the biomass from the producers to the higher trophic levels. The biomass here the net organisms collected from each feeding level and are then dried and weighed. This dry weight is the biomass and it represents the amount of energy available in the form of organic matter of the organisms. In this pyramid the net dry weight is plotted to that of the producers, herbivores, carnivores, etc. 

There are two types of pyramid of biomass, they are:

  • Upright pyramid of biomass and 

  • Inverted pyramid of biomass. 

Upright Pyramid of Biomass

This occurs when the larger net biomass of producers support a smaller weight of consumers. 

Example: Forest ecosystem. 


Inverted Pyramid of Biomass 

This happens when the smaller weight of producers support consumers of larger weight. 

Example: Aquatic ecosystem. 



 


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