ECOLOGICAL PYRAMIDS

An ecological pyramid is a graphical representation of the relationship between different organisms in an ecosystem. Each of the bars that make up the pyramid represents a different trophic level, and their order, which is based on who eats whom, represents the flow of energy. Energy moves up the pyramid, starting with the primary producers, or autotrophs, such as plants and algae at the very bottom, followed by  the primary consumers, which fed on these plants, then secondary consumers, which fed on the  primary consumers, and so on.  Ecological pyramids are prepared on the basis of number of organisms, their biomass and energy in each trophic level.

Ecological pyramids are mainly of three types: .

1. Pyramid of number

2. Pyramid of biomass

3. Pyramid of energy

1.  PYRAMID OF NUMBER

a)  It is the graphic representation of the number of organisms present in unit area of various trophic levels of a food chain with producers at the base and top consumers at the apex.

b) The pyramid of number may be inverted or upright.

c) Grassland, Pond and Forest Ecosystem are upright.

d) Parasites and tree Ecosystem are inverted in shape.

2. PYRAMID OF BIOMASS

a)It is the graphic representation of biomass of organisms present in unit area of various trophic levels of a food chain with the biomass of producers at the base and that of top carnivores at the apex. 

b)The pyramid of biomass of terrestrial ecosystem is upright or erect as there is gradual decrease in the biomass of organisms from the second trophic level to the final trophic level.

c) However, the pyramid of biomass of aquatic ecosystems (pond, lake, river etc). is inverted i.e. broad apex and tapering base which is because of the progressive increase in the biomass of the organisms from the second trophic level to the final trophic level.

d) In an aquatic ecosystem, most number of producers (algae) is microscopic and unicellular. They are more in number but their biomass is less than that of primary consumers.

e) The biomass of secondary consumers is more than that of primary consumers and the biomass of the final trophic level is the largest of all the trophic levels. Therefore, the pyramid of biomass of an aquatic ecosystem is always inverted.

f) Grassland and Forest Ecosystem are upright.

g) Pond  and water bodies are inverted .

3. PYRAMID OF ENERGY

a) A pyramid of energy is a graphical representation of the amount of energy at each trophic level of a food chain. They are expressed in units of energy per area per time.

b) Pyramids of energy will never appear inverted as some of the energy stored in one source is always lost upon transfer.

c) The amount of energy and matter transferred through food to successive higher levels become less and less. Greater amount of energy is available at the producer (autotrophs) level than at the primary consumer level (herbivores).

d) The energy production of primary consumer is greater than that of secondary consumers (primary carnivores) and the energy at the tertiary consumer level (top carnivores) is produced in minimum amount.