Editing Food web (section)

===Energy flow and biomass===
[[File:EnergyFlowFrog.jpg|thumb|upright=1.25|Energy flow diagram of a frog. The frog represents a node in an extended food web. The energy ingested is utilized for metabolic processes and transformed into biomass. The energy flow continues on its path if the frog is ingested by predators, parasites, or as a decaying [[Carrion|carcass]] in soil. This energy flow diagram illustrates how energy is lost as it fuels the metabolic process that transform the energy and nutrients into biomass.]]
{{main|Energy flow (ecology)}}
{{See also|Ecological efficiency}}
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| quote = The Law of Conservation of Mass dates from Antoine Lavoisier's 1789 discovery that mass is neither created nor destroyed in chemical reactions. In other words, the mass of any one element at the beginning of a reaction will equal the mass of that element at the end of the reaction.<ref name="Sterner11">{{cite journal | last1=Sterner | first1=R. W. | last2=Small | first2=G. E. | last3=Hood | first3=J. M. | title= The conservation of mass | journal=Nature Education Knowledge | volume=2 | issue=1 | page=11 | url=http://www.nature.com/scitable/knowledge/library/the-conservation-of-mass-17395478}}</ref>{{Rp|11}}
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[[File:EnergyFlowTransformity.jpg|thumb|upright=1.25|An expanded three link energy food chain (1. plants, 2. herbivores, 3. carnivores) illustrating the relationship between food flow diagrams and energy transformity. The transformity of energy becomes degraded, dispersed, and diminished from higher quality to lesser quantity as the energy within a food chain flows from one trophic species into another. Abbreviations: I=input, A=assimilation, R=respiration, NU=not utilized, P=production, B=biomass.<ref name="Odum88">{{cite journal | last1=Odum | first1=H. T. | s2cid=27517361 | year=1988 | title=Self-organization, transformity, and information |doi=10.1126/science.242.4882.1132 | journal=Science | volume=242 | issue=4882 | pages=1132–1139 | jstor=1702630 | pmid=17799729| bibcode=1988Sci...242.1132O | hdl=11323/5713 | hdl-access=free }}</ref>]]

Food webs depict energy flow via trophic linkages. Energy flow is directional, which contrasts against the cyclic flows of material through the food web systems.<ref name="Odum68">{{cite journal | last1=Odum | first1=E. P. | title=Energy flow in ecosystems: A historical review | journal=American Zoologist | year=1968 | volume=8 | issue=1 | pages=11–18 | doi=10.1093/icb/8.1.11 | doi-access=free }}</ref> Energy flow "typically includes production, consumption, assimilation, non-assimilation losses (feces), and respiration (maintenance costs)."<ref name="Benke10">{{cite journal | last1=Benke | first1=A. C. | title=Secondary production | journal=Nature Education Knowledge | volume=1 | issue=8 | page=5 | year=2010 | url=http://www.nature.com/scitable/knowledge/library/secondary-production-13234142}}</ref>{{rp|5}} In a very general sense, energy flow (E) can be defined as the sum of [[metabolism|metabolic]] production (P) and respiration (R), such that E=P+R.

Biomass represents stored energy. However, concentration and quality of nutrients and energy is variable. Many plant fibers, for example, are indigestible to many herbivores leaving grazer community food webs more nutrient limited than detrital food webs where bacteria are able to access and release the nutrient and energy stores.<ref name="Mann88">{{cite journal | last1=Mann | first1=K. H. | year=1988 | title=Production and use of detritus in various freshwater, estuarine, and coastal marine ecosystems | journal=Limnol. Oceanogr. | volume=33 | issue=2 | pages=910–930 | url=http://nospam.aslo.org/lo/toc/vol_33/issue_4_part_2/0910.pdf | doi=10.4319/lo.1988.33.4_part_2.0910 | url-status=dead | archive-url=https://web.archive.org/web/20120425235224/http://nospam.aslo.org/lo/toc/vol_33/issue_4_part_2/0910.pdf | archive-date=2012-04-25 | accessdate=2011-06-28 }}</ref><ref name="Kooijman04">{{cite journal | last1=Koijman | first1=S. A. L. M. | last2=Andersen | first2=T. | last3=Koo | first3=B. W. | title=Dynamic energy budget representations of stoichiometric constraints on population dynamics | journal=Ecology | volume=85 | issue=5 | pages=1230–1243 | year=2004 | url=http://www.bio.vu.nl/thb/research/bib/KooyAnde2004.pdf | doi=10.1890/02-0250| bibcode=2004Ecol...85.1230K }}</ref> "Organisms usually extract energy in the form of carbohydrates, lipids, and proteins. These polymers have a dual role as supplies of energy as well as building blocks; the part that functions as energy supply results in the production of nutrients (and carbon dioxide, water, and heat). Excretion of nutrients is, therefore, basic to metabolism."<ref name="Kooijman04" />{{rp|1230–1231}} The units in energy flow webs are typically a measure mass or energy per m<sup>2</sup> per unit time. Different consumers are going to have different metabolic assimilation efficiencies in their diets. Each trophic level transforms energy into biomass. Energy flow diagrams illustrate the rates and efficiency of transfer from one trophic level into another and up through the hierarchy.<ref name="Andersen09">{{cite journal | last1=Anderson | first1=K. H. | last2=Beyer | first2=J. E. | last3=Lundberg | first3=P. | title=Trophic and individual efficiencies of size-structured communities | journal=Proc Biol Sci | year=2009 | volume=276 | issue=1654 | pages=109–114 | doi=10.1098/rspb.2008.0951 | pmc=2614255 | pmid=18782750}}</ref><ref name="Benke11">{{cite journal | last1=Benke | first1=A. C. | year=2011 | title=Secondary production, quantitative food webs, and trophic position | journal=Nature Education Knowledge | volume=2 | issue=2 | page=2 | url=http://www.nature.com/scitable/knowledge/library/secondary-production-quantitative-food-webs-and-trophic-17653963}}</ref>

It is the case that the [[biomass]] of each [[trophic level]] decreases from the base of the chain to the top. This is because energy is lost to the environment with each transfer as [[entropy]] increases. About eighty to ninety percent of the energy is expended for the organism's life processes or is lost as heat or waste. Only about ten to twenty percent of the organism's energy is generally passed to the next organism.<ref name="entropy">{{cite book | last= Spellman| first= Frank R.| title= The Science of Water: Concepts and Applications| year= 2008| publisher= CRC Press| page= 165| url= https://books.google.com/books?id=Grivqd7tLuAC&q=%22is+lost+as+heat+and+wastes%22&pg=PA165| isbn= 978-1-4200-5544-3}}</ref> The amount can be less than one percent in [[animals]] consuming less digestible plants, and it can be as high as forty percent in [[zooplankton]] consuming [[phytoplankton]].<ref>{{cite book | last= Kent| first= Michael| title= Advanced Biology| year= 2000| publisher= Oxford University Press US| page= 511| url= https://books.google.com/books?id=8aw4ZWLABQkC&q=%22trophic+efficiency+of+less+than+1%25%22&pg=PA511| isbn= 978-0-19-914195-1}}</ref> Graphic representations of the biomass or productivity at each tropic level are called [[ecological pyramid]]s or trophic pyramids. The transfer of energy from primary producers to top consumers can also be characterized by energy flow diagrams.<ref>{{cite book | last= Kent| first= Michael| title= Advanced Biology| year= 2000| publisher= Oxford University Press US| page= 510| url= https://books.google.com/books?id=8aw4ZWLABQkC&q=%22by+an+energy+flow+diagram%22&pg=PA510| isbn= 978-0-19-914195-1}}</ref>