Ecologic pyramids are diagrams of data representing the standing crops at each trophic level. The first attempt to provide a quantitative law concerning the trophic level in a community was given by an English ecologist Elton (1927). lie coined the term pyramid of numbers in the different stages of a food chain commonly observed in the field.
He visualized that the food chain accompained by concommitant energy losses at each step was not only an elegant flowing model but also as a static pyramid. Pyramid of numbers helped protray the relative numbers of organisms at each of the 4 trophic levels – producers, herbivores and two levels of predators in a forest or a lake ecosystem. However, the existence of parasites frequently leads to inverted pyaramids of numbers. Again, inverted pyramids of numbers result when, for instance, a single tree support much smaller organisms
Pyramids of biomass were thought to be more representative than mere numbers in successive trophic stages in a community. As the name suggests, pyramids of biomass arc calculated, by determining for a given unit area, the biomass of producers, the biomass
Pyramids of Numbers: A. Grass land; B. Pond; C. Forests of herbivores, the biomass of first level carnivore and so on.
It is a fact that very few pyramids of biomass have ever been determined, for this is quite a difficult and time-consuming job, although it is likely to remain pyramidal in shape and not inverted. However, in the oceans where the rate of reproduction of the phytoplankton is much greater due to their much smaller size, may support a larger mass of zooplankton at certain time in a year. Here again, the pyramid may appear inverted.
There is a third sort of ecologic pyramid to indicate the trophic relationships within a community. This is the pyramid of energy. It shows the flow of energy from one trophic level of a community to the next. The units of pyramids of energy are energy / area / time i.e. kJ / ha / yr. It shows the rate at which energy flows up a food web, measured over a stated period of time.
Theoretically, the pyramid of energy can never by invert. This flows directly as per the first law of thermodynamics or the law of conservation of energy which states that energy can neither be created nor destroyed but is always conserved.
It is worth emphasizing that the pyramid of energy gives complete information only on the flow of energy in an ecosystem. It should not be seen as “better” than pyramids of numbers or biomass, since an ecologist seeks different kinds of information in different ecosystms and therefore, applies different kinds of pyramidal studies depending on data of interest.