Ecological pyramids

 Ecological pyramids

Graphic representation of tropics structure and function of ecosystem, starting with producers at the base and successive tropic levels forming The apex is known as logical pyramid. 

Ecological pyramids are of three types:

1. Pyramid of numbers: it represent the number of individual organisms at each trophic level. We may have upright or inverted pyramid of numbers, depending upon the type of ecosystem and food chain. A grassland ecosystem and a pond ecosystem show at applied pyramid of numbers. The producers in the grasslands are grass and that in a pond are phytoplankton (algae etc.), Which are small in size and very large in number. So, the producers form a broad base. The herbivores in grasslands are insects while tertiary carnivores are hawks or other birds which are gradually less and less in number and hence the pyramid apex becomes gradually narrower forming and upright pyramid. Similar is the case with the herbivorous, carnivorous and top carnivorous in pond which decrease in number at higher tropic level.

In a forest ecosystem, big trees are the producers which are less than number and hence form a narrow base. A largest number of herbivorous including birds, insects and several species of animals feed upon the trees (on leaves, fruits, flowers, bark etc.) and form a much broader middle level. The secondary consumers like fox, snakes, lizards etc. are less in number than herbivorous while top carnivorous like lion, tiger etc. are still smaller in number.  So the pyramid is narrow on both sides and broader in the middle.

Parasitic food chain shows an inverted pyramid of number. The producers like a few big trees harbor fruit eating birds acting like herbivorous which are larger in number. A much higher number of lice, bugs etc. grow as parasites on these birds while a still greater number of hyper-parasites like bugs, fleas and microbes feed upon them, thus making an inverted pyramid.

2. Pyramid of biomass: It is based upon the total biomass (dry matter) at each tropic level in a food chain. The pyramid of biomass can also be upright or inverted. The pyramid of biomass in a forest is upright in contrast to its pyramid of numbers. This is because the producers (trees) accumulate a huge biomass while the consumers, total biomass feeding on them declines at higher tropic levels, resulting in in broad base and narrowing top.

The pond ecosystem shows an inverted pyramid of biomass. The total biomass of producers (phytoplankton) is much less as compared to herbivorous (zooplankton, insects), carnivores (small fish) and tertiary carnivores (big fish). Thus the pyramid takes an inverter shape with narrow base and broad apex.

3. Pyramid of energy: The amount of energy present at each tropic level is considered for this type of pyramid. Pyramid of energy give the the best representation of the tropic relationships and it is always upright.

At every successive trophic level, there is a huge loss of energy (about 90%) in the form of heat, respiration etc. Thus, at each next higher level only 10% of the energy passes on. Hence, there is a sharp decline in energy e level of each successive trophic level as we move from producers to top carnivores. Therefore, the pyramid of energy is always upright.