Ecological Pyramids:- In any ECOSYSTEM, a relationship exists between the individuals of biotic component with reference to the food chain. This relationship between individuals like Producers Herbivores Carnivores, can be shown digrammatically by means of Ecological pyramids. These pyramids where first given by a British Ecologist Charles Elton in 1927, hence they are called ELTONIAN PYRAMIDS.
A simple ecological pyramid showing the different trophic levels.
An ecological pyramid is a graphical representation of an parameter like number of individuals or amount of biomass, energy present in the various trophic levels of a food chain with producer forming the base. The shape of the pyramid may be upright, inverted, spindle shaped etc. The ecological pyramids can be divided into three types 1. Pyramid of Numbers 2. Pyramid of Biomass 3. Pyramid of Energy.
1. Pyramid of Numbers:- The pyramid of numbers shows the relationship between producers, carnivores and the omnivores in terms of their numbers. Mostly the pyramid of numbers is straight or upright with the number of individuals in the successive trophic level decreases from base to the apex. Maximum number is assumed at producer level and minimum at the omnivore level, hence appears upright.
2. Pyramid of Biomass:- The amount of living or organic matter present in the environment is called Biomass. This pyramid shows the relationship between the living matter at different trophic levels. The pyramid of biomass is upright in terrestrial ecosystem and inverted in aquatic ecosystem.
3. Pyramid of Energy:- The pyramid of energy shows the flow of energy from one trophic level of a community to the next. The shape of pyramid is always UPRIGHT [since the total energy at each level is calculated]. The energy content is generally expressed as K. cal / m / yr. Maximum energy content is present in the producers and as the energy passes on in the food chain it decreases, because of its utilization in performing life activities.
Energy Flow In Ecosystem:- The functioning of the ecosystem depends upon the flow of energy through matter. Energy enters the system through solar radiation and gets converted to chemical energy passes through each of the trophic level. The one way flow of energy is observed in the ecosystem which is governed by two laws:
First Law:- Energy may be transformed from one state to another, but can neither be created nor destroyed. Second Law:- Every transformation of energy is accompanied by some dispersion or loss of energy in the form of heat.
Energy Flow Is Unidirectional:- In an Ecosystem, the producers prepare the food utilizing the solar energy. This energy is now in the form of food, moves through the trophic levels in a particular direction. The flow of energy is always unidirectional from producers to consumers. Energy cannot be transformed in reverse direction i.e consumers to producers.
Gradual Decrease In The Amount Of Energy:- The amount of energy transferred decreases with successive trophic levels. Producers capture only a small fraction of solar energy part of which is utilized in the bodily functions and the remaining is transferred to the next trophic level. Hence the energy from the producers to the consumers reduces gradually.
The ratio between energy flow at different points along the chain expressed as percentage is called ECOLOGICAL EFFICIENCY. Slobodkin (1959) suggested that the transfer of energy from one trophic level to the next is of the order of 10% and this is termed as. GROSS ECOLOGICAL EFFICIENCY Thus if there are 100 calories of NP at producer level, only 10 calories of secondary production would be expected at the herbivore level, only 1 calorie at first carnivore level and so on. This can be called as TEN PERCENT RULE.