Any food chain does not use all the food for the growth of individuals, i.e., the formation of biomass. Part of it is spent on meeting organism energy consumption: respiration, movement, reproduction, body temperature, etc. Therefore, in each subsequent link of the food chain there is a reduction of biomass. Usually the larger the mass of the initial link of the food chain, the more it is in subsequent links.
Food chain is the main channel of energy transfer in the community. The further from the primary producer, the lesser the volume. There are several reasons.
Energy transfer from one level to another is never complete. Some of the energy is lost during food processing, and some is not absorbed by the body and is derived from his excrement, and then is decomposed by destructors.
Some of the energy is lost as heat during respiration. Any animal, traveling, hunting, building a nest or other actions, doing work that requires energy, causing the heat release again.
Decrease in the amount of energy in the transition from one trophic level to another (higher) determines the number of levels and the ratio of predators and prey. It is estimated that any given trophic level receives about 10% (or slightly more) of the energy of the previous level. Therefore the total number of trophic levels is rarely more than four or six.
This phenomenon is illustrated graphically, has been called ecological pyramid. Distinguish population pyramid, biomass pyramid, and energy pyramid.
Plants are producers and they form the base of the pyramid. Above them are located consumers of the first level (herbivores).
Consumers of the second level are predators. And so on until the top of the pyramid, which is occupied by the large predators? The height of the pyramid normally corresponds to the length of the food chain.
The biomass pyramid of organisms shows the biomass ratio of various trophic levels graphically depicted in such a manner that the length or area of the rectangle corresponding to the specific trophic level proportional to biomass.
The population pyramid reflects the population density of organisms at each trophic level.
Importantly, the biomass pyramid and population pyramids do not take into account the rate of self-reproduction of the organisms! If the reproduction rate of the population of the prey is high, even at low biomass such a population may be sufficient food source for predators, having a higher biomass, but the low rate of reproduction. For this reason, the biomass pyramid and population pyramids can be inverted, i.e., the lowest trophic levels may have less density and biomass, than the highest, for example, on one tree can live and feed on many insects (inverted pyramid of numbers). The inverted biomass pyramid is peculiar for sea ecosystem, where primary producers (phytoplankton algae) have very rapid rate of reproduction, and their consumers (zooplankton crustaceans) is much larger, but they multiply much more slowly. Marine vertebrates have even more weight and a longer cycle of reproduction.