Pyramid of numbers
- shows the number of organisms at each trophic level
- each consecutive level contains fewer organisms than the level below it
- thus the number of herbivores like zebras is greater than the carnivores like lions
The shape of the pyramid of numbers vary from ecosystem to ecosystem.
eg,
In aquatic ecosystems and herbaceous communities, autotrophs are present in large numbers per unit area. They support a lesser number of herbivores, which inturn support fewer carnivores.
So, the producers are smallest sized but maximum in number while carnivores are larger in size but lesser in number, so these cannot be used as prey by another.
Hence the pyramid of numbers is upright.
Pyramid of biomass
- shows the total biomass at each successive trophic level
- biomass is the total amount of living matter at a trophic level
- the pyramids of mass show a progressive reduction of biomass in the successive trophic level
- an enormous mass of grass is required to support a smaller mass of buck, which in turn would support a smaller mass of lions.
In a terrestrial ecosystem, the maximum biomass occurs in producers, and there is progressive decrease in biomass from lower to higher trophic levels. Thus, the pyramid of biomass in a terrestrial ecosystem is upright.
Pyramid of energy
- indicates the total amount of energy present in each trophic level
- shows the loss of energy from one trophic level to the next as food is transferred from one trophic level to the next
Energy is lost:
1) as heat during respiration at every trophic level
2) in uneaten parts
3) through undigested matter egested by consumers
4) through waste products excreted consumers, eg, urea
Pyramid of energy is always upright.
It is so because at each transfer about 80 - 90% of the energy available at lower trophic level is used up to overcome its entropy and to perform metabolic activities. Only 10% of the energy is available to next trophic level (as per Lindemann's ten percent rule), so there are usually no more than 4 or 5 links in a food chain.
Going up each level of the pyramid, less and less energy is available. The number of organisms the pyramid can support is small. This explains why there are typically more prey than predators in a community. Thus, the pyramid of numbers, the pyramid of biomass and the pyramid of energy all describe relationships among organisms in a single ecosystem.
Variations
- In a parasitic food chain, for e.g., an oak tree, the large tree provides food to several herbivorous birds. The birds support larger population of ectoparasites leading to the formation of an inverted pyramid.
When a large tree support larger number of herbivorous birds which inturn are eaten by carnivorous birds like falcon and eagle, which are smaller in number, it forms a spindle shaped pyramid.
- In an aquatic habitat the pyramid of biomass is inverted or spindle shaped where the biomass of trophic level depends upon the reproductive potential and longivity of the member.
