TROPHIC LEVEL PYRAMIDS AND THEIR TYPES

Trophic level is defined as the position of organism in the food chain. Food chain is a sequence of organisms that eat the other organism and in turn are eaten themselves. At base level are primary producers that are plants, they are eaten by second level herbivores, At third level are predators or 1st level carnivores that eat herbivores. At 4 and 5 level apex predators or carnivores are present. 

TROPHIC PYRAMIDS

Trophic pyramids are the graphical representation designed to show the number, biomass, bio productivity and energy at each trophic level. These pyramids are divided into 3 types: pyramids of biomass, pyramids of numbers and pyramids of energy.

Trophic Pyramids

PYRAMIDS OF NUMBERS

Food webs describes the relation of feeding among the organisms in a community. But these are not quantitative. The first time concept of quantitative study of trophic levels was given by Elton. By studying a wood oak we see increase number of small herbivorous insects such as aphids, good number of small warblers, large number of carnivores ground beetles and spiders and one or two hawks. In same way in a small pond protozoa number goes to million. Daphnia and Cyclops number is in thousands, and few fishes. The animals at the base are comparatively high  and at the end they are fewer. Small herbivores can increase their number They could enhance their number they have margin to increase their number above which they they maintain their population in absence of enemies. This margin supports carnivores that are larger in size but low in numbers. These carnivores further have low margin owing to their large size and make them increase slowly and low in numbers.

Elton in his observation pointed neither producers or decomposers. He pointed the term pyramid of numbers. He found that it is difficult to get actual number of individuals at different stage of food chain. Pyramids of numbers have the units of individuals/area.

PYRAMIDS OF BIOMASS

Ecologists find that some pyramids are inverted due to large size of producers or small size of parasites. So they need to determine pyramids of biomass. 

Pyramids of Biomass are calculated by calculating the biomass of producers, biomass of herbivores, biomass of 1 st level carnivores and so on.

Pyramid of Biomass can never be inverted. The reason behind this are not theoretical. One reason is in case of phytoplankton are source of food for zooplankton. The mass of phytoplankton best supports the large number of zooplankton. The rate of reproduction of phytoplankon is much higher because of its small size. The turnover of phytoplankton is much higher than the turnover of zooplankton. Pyramids of biomass have the units of mass/area.

PYRAMID OF ENERGY

The flow of energy from one trophic level to the other is described by the Pyramid of Energy. 

The units are energy/area/time, e.g. kJ/ha/yr. It shows the rate of flow of energy in food web. Pyramids of Energy can not be inverted because it follows the first law of thermodynamics that states  energy is neither created nor destroyed and it is always conserved.