ten percent law
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Ecological efficiency describes the efficiency with which
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 ...
is transferred from one
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 ...
to the next. It is determined by a combination of efficiencies relating to organismic resource acquisition and assimilation in an ecosystem.


Energy transfer

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 ...
occurs in
autotroph An autotroph or primary producer is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) using carbon from simple substances such as carbon dioxide,Morris, J. et al. (2019). "Biology: How Life Wo ...
ic organisms of an
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 ...
.
Photoautotroph Photoautotrophs are organisms that use light energy and inorganic carbon to produce organic materials. Eukaryotic photoautotrophs absorb energy through the chlorophyll molecules in their chloroplasts while prokaryotic photoautotrophs use chlorophyl ...
s such as
vascular plant Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They ...
s and algae convert energy from the sun into energy stored as carbon compounds.
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 ...
is carried out in the chlorophyll of green plants. The energy converted through photosynthesis is carried through the trophic levels of an ecosystem as organisms consume members of lower trophic levels. Primary production can be broken down into gross and net primary production. Gross primary production is a measure of the energy that a photoautotroph harvests from the sun. Take, for example, a blade of grass that takes in ''x''
joule The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applie ...
s of energy from the sun. The fraction of that energy that is converted into
glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...
reflects the gross productivity of the blade of grass. The energy remaining after respiration is considered the net primary production. In general, gross production refers to the energy contained within an organism before respiration and net production the energy after respiration. The terms can be used to describe energy transfer in both autotrophs and
heterotroph 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 ...
s. Energy transfer between trophic levels is generally inefficient, such that net production at one trophic level is generally only 10% of the net production at the preceding trophic level (the Ten percent law). Due to non-predatory death,
egestion Defecation (or defaecation) follows digestion, and is a necessary process by which organisms eliminate a solid, semisolid, or liquid waste material known as feces from the digestive tract via the anus. The act has a variety of names ranging fro ...
, and
cellular respiration Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive the bulk production of ATP. Cellular respiration may be des ...
, a significant amount of energy is lost to the environment instead of being absorbed for production by consumers. The figure approximates the fraction of energy available after each stage of energy loss in a typical ecosystem, although these fractions vary greatly from ecosystem to ecosystem and from trophic level to trophic level. The loss of energy by a factor of one half from each of the steps of non-predatory death, defecation, and respiration is typical of many living systems. Thus, the net production at one trophic level is 1/2*1/2*1/2 = 1/8 or approximately ten percent that of the trophic level before it. For example, assume 500 units of energy are produced by trophic level 1. One half of that is lost to non-predatory death, while the other half (250 units) is ingested by trophic level 2. One half of the amount ingested is expelled through defecation, leaving the other half (125 units) to be assimilated by the organism. Finally one half of the remaining energy is lost through respiration while the rest (63 units) is used for growth and reproduction. This energy expended for growth and reproduction constitutes to the net production of trophic level 1, which is equal to 500 * 1/2 *1/2 * 1/2 = 63 units.


Quantifying ecological efficiency

Ecological efficiency is a combination of several related efficiencies that describe resource utilization and the extent to which resources are converted into biomass. * Exploitation efficiency is the amount of food ingested divided by the amount of
prey Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill ...
production (I_n/P_) * Assimilation efficiency is the amount of assimilation divided by the amount of food
ingestion Ingestion is the consumption of a substance by an organism. In animals, it normally is accomplished by taking in a substance through the mouth into the gastrointestinal tract, such as through eating or drinking. In single-celled organisms in ...
(A_n/I_n) * Net Production efficiency is the amount of consumer production divided by the amount of assimilation (P_n/A_n) * Gross Production efficiency is the assimilation efficiency multiplied by the net production efficiency, which is equivalent to the amount of consumer production divided by amount of ingestion (P_n/I_n) * Ecological efficiency is the exploitation efficiency multiplied by the assimilation efficiency multiplied by the net production efficiency, which is equivalent to the amount of consumer production divided by the amount of prey production (P_n/P_) Theoretically, it is easy to calculate ecological efficiency using the mathematical relationships above. It is often difficult, however, to obtain accurate measurements of the values involved in the calculation. Assessing ingestion, for example, requires knowledge of the gross amount of food consumed in an
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 ...
as well as its caloric content. Such a measurement is rarely better than an educated estimate, particularly with relation to ecosystems that are largely inaccessible to ecologists and tools of measurement. The ecological efficiency of an ecosystem is as a result often no better than an approximation. On the other hand, an approximation may be enough for most ecosystems, where it is important not to get an exact measure of efficiency, but rather a general idea of how energy is moving through its
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 ...
s.


Applications

In agricultural environments, maximizing
energy transfer 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 heat ...
from producer (food) to
consumer A consumer is a person or a group who intends to order, or uses purchased goods, products, or services primarily for personal, social, family, household and similar needs, who is not directly related to entrepreneurial or business activities. ...
(
livestock Livestock are the domesticated animals raised in an agricultural setting to provide labor and produce diversified products for consumption such as meat, eggs, milk, fur, leather, and wool. The term is sometimes used to refer solely to animal ...
) can yield economic benefits. A sub-field of agricultural science has emerged that explores methods of monitoring and improving ecological and related efficiencies. In comparing the net efficiency of energy utilization by cattle, breeds historically kept for
beef production The meat industry are the people and companies engaged in modern industrialized livestock agriculture for the production, packing, preservation and marketing of meat (in contrast to dairy products, wool, etc.). In economics, the meat industry ...
, such as the Hereford, outperformed those kept for dairy production, such as the Holstein, in converting energy from feed into stored energy as tissue. This is a result of the beef cattle storing more body fat than the dairy cattle, as energy storage as protein was at the same level for both breeds. This implies that cultivation of cattle for slaughter is a more efficient use of feed than is cultivation for milk production. While it is possible to improve the efficiency of energy use by livestock, it is vital to the world food question to also consider the differences between animal husbandry and plant agriculture. Caloric concentration in
fat tissue Adipose tissue, body fat, or simply fat is a loose connective tissue composed mostly of adipocytes. In addition to adipocytes, adipose tissue contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, vascular en ...
s are higher than in plant tissues, causing high-fat organisms to be most energetically-concentrated; however, the energy required to cultivate feed for livestock is only partially converted into fat cells. The rest of the energy input into cultivating feed is respired or egested by the livestock and unable to be used by humans. Out of a total of of energy used in the US in 1999, 10.5% was used in food production, with the percentage accounting for food from both producer and primary consumer
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 ...
s. In comparing the cultivation of animals versus plants, there is a clear difference in magnitude of energy efficiency. Edible kilocalories produced from kilocalories of energy required for cultivation are: 18.1% for chicken, 6.7% for grass-fed beef, 5.7% for farmed salmon, and 0.9% for shrimp. In contrast, potatoes yield 123%, corn produce 250%, and soy results in 415% of input calories converted to calories able to be utilized by humans. This disparity in efficiency reflects the reduction in production from moving up trophic levels. Thus, it is more energetically efficient to form a diet from lower trophic levels.


Ten percent law

The ten percent law of transfer of energy from one
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 ...
to the next can be attributed to
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), although Lindeman did not call it a "law" and cited ecological efficiencies ranging from 0.1% to 37.5%. According to this law, during the transfer of organic food energy from one trophic level to the next higher level, only about ten percent of the transferred energy is stored as flesh. The remaining is lost during transfer, broken down in respiration, or lost to incomplete
digestion Digestion is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma. In certain organisms, these smaller substances are absorbed through the small intest ...
by higher trophic level.


10% law

When organisms are consumed, approximately 10% of the energy in the food is fixed into their flesh and is available for next trophic level (
carnivores A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other so ...
or
omnivores An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nut ...
). When a carnivore or an omnivore in turn consumes that animal, only about 10% of energy is fixed in its flesh for the higher level. For example, the Sun releases 10,000 J of energy, then plants take only 100 J of energy from sunlight (exception- Only 1% of energy is taken up by plants from sun); thereafter, a deer would take 10 J (10% of energy) from the plant. A wolf eating the deer would only take 1 J (10% of energy from deer). A human eating the wolf would take 0.1J (10% of energy from wolf), etc. The ten percent law provides a basic understanding on the cycling of food chains. Furthermore, the ten percent law shows the inefficiency of energy capture at each successive trophic level. The rational conclusion is that energy efficiency is best preserved by sourcing food as close to the initial energy source as possible.


Formula

Energy at n(th) level = (energy given by sun)/(10)^(n+1), and, Energy at n(th) level = (energy given by plant)/(10)^(n-1)


See also

*
Eco-efficiency As countries and regions around the world began to develop, it slowly became evident that industrialization and economic growth come hand in hand with environmental degradation. Eco-efficiency has been proposed as one of the main tools to promote a ...
- the economic efficiency with which human society uses ecological resources


References

{{DEFAULTSORT:Ecological Efficiency Trophic ecology