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An ecological pyramid (also trophic pyramid, Eltonian pyramid, energy pyramid, or sometimes food pyramid) is a graphical representation designed to show the biomass or bioproductivity at each
trophic level The trophic level of an organism is the position it occupies in a food web. A food chain is a succession of organisms that eat other organisms and may, in turn, be eaten themselves. The trophic level of an organism is the number of steps it ...
in a given
ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...
. A ''pyramid of energy'' shows how much energy is retained in the form of new biomass at each trophic level, while a ''pyramid of biomass'' shows how much biomass (the amount of living or organic matter present in an organism) is present in the organisms. There is also a ''pyramid of numbers'' representing the number of individual organisms at each trophic level. Pyramids of energy are normally upright, but other pyramids can be inverted or take other shapes. Ecological pyramids begin with
producers Producer or producers may refer to: Occupations *Producer (agriculture), a farm operator *A stakeholder of economic production *Film producer, supervises the making of films **Executive producer, contributes to a film's budget and usually does not ...
on the bottom (such as plants) and proceed through the various trophic levels (such as herbivores that eat plants, then carnivores that eat flesh, then omnivores that eat both plants and flesh, and so on). The highest level is the top of the
food chain A food chain is a linear network of links in a food web starting from producer organisms (such as grass or algae which produce their own food via photosynthesis) and ending at an apex predator species (like grizzly bears or killer whales), de ...
. Biomass can be measured by a bomb calorimeter.


Pyramid of energy

A ''pyramid of energy'' or ''pyramid of productivity'' shows the production or turnover (the rate at which energy or mass is transferred from one trophic level to the next) of biomass at each trophic level. Instead of showing a single snapshot in time,
productivity Productivity is the efficiency of production of goods or services expressed by some measure. Measurements of productivity are often expressed as a ratio of an aggregate output to a single input or an aggregate input used in a production proces ...
pyramids show the flow of
energy In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of hea ...
through the
food chain A food chain is a linear network of links in a food web starting from producer organisms (such as grass or algae which produce their own food via photosynthesis) and ending at an apex predator species (like grizzly bears or killer whales), de ...
. Typical units are grams per square meter per year or calories per square meter per year. As with the others, this graph shows producers at the bottom and higher trophic levels on top. When an ecosystem is healthy, this graph produces a standard ''ecological pyramid''. This is because, in order for the ecosystem to sustain itself, there must be more energy at lower trophic levels than there is at higher trophic levels. This allows organisms on the lower levels to not only maintain a stable population, but also to transfer energy up the pyramid. The exception to this generalization is when portions of a
food web A food web is the natural interconnection of food chains and a graphical representation of what-eats-what in an ecological community. Another name for food web is consumer-resource system. Ecologists can broadly lump all life forms into one o ...
are supported by inputs of resources from outside the local
community A community is a social unit (a group of living things) with commonality such as place, norms, religion, values, customs, or identity. Communities may share a sense of place situated in a given geographical area (e.g. a country, village, ...
. In small, forested streams, for example, the volume of higher levels is greater than could be supported by the local
primary production In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through ...
. Energy usually enters ecosystems from the Sun. The primary producers at the base of the pyramid use solar radiation to power
photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...
which produces food. However most wavelengths in solar radiation cannot be used for photosynthesis, so they are reflected back into space or absorbed elsewhere and converted to heat. Only 1 to 2 percent of the energy from the sun is absorbed by photosynthetic processes and converted into food. When energy is transferred to higher trophic levels, on average only about 10% is used at each level to build biomass, becoming stored energy. The rest goes to metabolic processes such as growth, respiration, and reproduction. Advantages of the ''pyramid of energy'' as a representation: * It takes account of the rate of production over a period of time. * Two species of comparable biomass may have very different life spans. Thus, a direct comparison of their total biomasses is misleading, but their productivity is directly comparable. * The relative energy chain within an ecosystem can be compared using pyramids of energy; also different
ecosystems An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...
can be compared. * There are no inverted pyramids. * The input of solar energy can be added. Disadvantages of the ''pyramid of energy'' as a representation: * The rate of biomass production of an organism is required, which involves measuring growth and reproduction through time. * There is still the difficulty of assigning the organisms to a specific trophic level. As well as the organisms in the food chains there is the problem of assigning the
decomposers Decomposers are Organism, organisms that break down dead or decaying organisms; they carry out decomposition, a process possible by only certain kingdoms, such as fungi. Like herbivores and predators, decomposers are heterotrophic, meaning that t ...
and detritivores to a particular level.


Pyramid of biomass

A ''pyramid of biomass'' shows the relationship between biomass and trophic level by quantifying the biomass present at each trophic level of an ecological community at a particular time. It is a graphical representation of biomass (total amount of living or organic matter in an ecosystem) present in unit area in different trophic levels. Typical units are grams per square meter, or calories per square meter. The pyramid of biomass may be "inverted". For example, in a pond ecosystem, the
standing crop A standing crop is the total biomass of the living organisms present in a given environment. This includes both natural ecosystems and agriculture Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the ...
of phytoplankton, the major
producers Producer or producers may refer to: Occupations *Producer (agriculture), a farm operator *A stakeholder of economic production *Film producer, supervises the making of films **Executive producer, contributes to a film's budget and usually does not ...
, at any given point will be lower than the mass of the
heterotrophs A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...
, such as fish and insects. This is explained as the phytoplankton
reproduce Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. Reproduction is a fundamental feature of all known life; each individual org ...
very quickly, but have much shorter individual lives.


Pyramid of numbers

A ''pyramid of numbers'' shows graphically the population, or abundance, in terms of the number of individual organisms involved at each level in a food chain. This shows the number of organisms in each trophic level without any consideration for their individual sizes or biomass. The pyramid is not necessarily upright. For example, it will be inverted if beetles are feeding from the output of forest trees, or parasites are feeding on large host animals.


History

The concept of pyramid of numbers ("Eltonian pyramid") was developed by Charles Elton (1927). Later, it would also be expressed in terms of biomass by Bodenheimer (1938). The idea of pyramid of productivity or energy relies on works of G. Evelyn Hutchinson and
Raymond Lindeman Raymond Laurel Lindeman (1915 – June 29, 1942) was an ecologist whose graduate research is credited with being a seminal study in the field of ecosystem ecology, specifically on the topic of trophic dynamics. Graduate research work Lindeman ...
(1942).Lindeman, R. L. (1942). The trophic-dynamic aspect of ecology. ''Ecology'' 23: 399–418
link


See also

*
Trophic cascade Trophic cascades are powerful indirect interactions that can control entire ecosystems, occurring when a trophic level in a food web is suppressed. For example, a top-down cascade will occur if predators are effective enough in predation to reduce t ...


References


Bibliography

*Odum, E.P. 1971. Fundamentals of Ecology. Third Edition.
W.B. Saunders Company Saunders is an American academic publisher based in the United States. It is currently an imprint of Elsevier. Formerly independent, the W. B. Saunders company was acquired by CBS in 1968, who added it to their publishing division Holt, Rinehart ...
, Philadelphia,


External links


Food Chains
{{DEFAULTSORT:Ecological Pyramid Ecology