Monday, September 15, 2014

Ecological pyramids

Ecological Pyramid
Ecological pyramids are of three types:
i. Pyramid of numbers
ii. Pyramid of energy
iii. Pyramid of biomass
The concept of ecological pyramid was developed by Charles Elton; these pyramids are also known as Eltonian pyramids. The pyramids are a graphical representation which depicts the number of organisms, biomass and productivity at each trophic level. All ecological pyramids begin at the bottom with the produces and proceed through different trophic levels. 

Ecological pyramids begin with the producers at the bottom like plants and they proceed to various trophic levels like herbivores consume plants, carnivores prey on herbivores and so on. The highest level is at the top of the food chain.  

Ecological Pyramid

Consider a grassland ecosystem for example:
In a grassland ecosystem, the producer is grass which is small in size but large in number. Hence, it
occupies the lowest trophic level (I trophic level).
The primary consumers are rats (herbivores) and they are more in number than grass. Therefore they
occupy the second trophic level (II trophic level)
The secondary consumers are snakes (carnivores) and they are fewer in number than the rats. They
occupy the third trophic level(III trophic level)
Eagles are the tertiary consumers that feed on snakes and they are at the top of the pyramid with the
least in number. They form the apex in the pyramid of numbers. The diagram is shown above which is self-explanatory.
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 Energy
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.

Pyramid of Number
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.

Partly Upright Pyramid of Number
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.

Inverted Pyramid of Number
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.

Biomass Upright Pyramid in Terrestrial Ecosystem

Inverted Pyramid of Biomass
This happens when the smaller weight of producers support consumers of larger weight.
Example: Aquatic ecosystem.

Inverted Pyramid of Biomass in Aquatic Ecosystem


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