Page 4 - Lesson note-Ecosytem

Each tropic level has a certain mass of living material at particular time called as standing

crop. It is measured as biomass of living organism or number in unit area.

The number of trophic levels in the grazing food chain is limited as the transfer of energy

follows 10 percent law that is only 10 percent of the energy is transferred to each trophic
level from the lower trophic level. In GFC, following trophic levels are possible- producer,

herbivore, primary carnivore, secondary carnivore.

Ecological Pyramids

Ecological pyramid is the graphical representation of an ecological parameter (number,

biomass, energy) sequence wise in various trophic levels of a food chain with producers at
the base and herbivores in the middle and carnivores at the top tiers. It can be upright,

inverted, or spindle shaped.

Three common ecological pyramids are

a) Pyramids of number- employs the number of individuals per unit area at various trophic

levels with producer at base and various consumers at successively higher levels. It is

generally upright.

A pyramid of number in case of a big tree is generally inverted because number of

insects feeding on that tree generally exceeds in number.

b) Pyramids of biomass- represent the biomass in various trophic levels. A pyramid of mass

is upright except in aquatic food chain involving short lived plankton.

A pyramid of biomass in sea is generally inverted because biomass of fishes generally

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