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Biomass, in ecology, is the mass of living biological organisms in a given area or ecosystem at a given time. Biomass can refer to species biomass, which is the mass of one or more species, or to community biomass, which is the mass of all species in the community. It can include microorganisms, plants or animals.[1] The mass can be expressed as the average mass per unit area, or as the total mass in the community. It might be measured in grams per square metre or tonnes per square kilometre, or it might be measured as the total mass present in a system such as a lake.

How biomass is measured depends on why it is being measured. Sometimes the biomass is regarded as the natural mass of organisms in situ, just as they are. For example, in a salmon fishery, the salmon biomass might be regarded as the total wet weight the salmon would have if they were taken out of the water. In other contexts, biomass can be measured in terms of the dried organic mass, so perhaps only 30% of the actual weight might count, the rest being water. For other purposes, only biological tissues count, and teeth, bones and shells are excluded. In stricter scientific applications, biomass is measured as the mass of organically bound carbon (C) that is present.

Contents

Ecological pyramids

An ecological pyramid.

An ecological pyramid is a graphical representation which shows, for a given ecosystem, the relationship between biomass or biological productivity and trophic levels.

  • A biomass pyramid shows the amount of biomass at each trophic level.
  • A productivity pyramid shows the production or turn-over in biomass at each trophic level.

An ecological pyramid provides a snapshot in time of an ecological community.

The bottom of the pyramid represents the primary producers (autotrophs). The primary producers take energy from the environment in the form of sunlight or inorganic chemicals and use it to create energy-rich molecules such as carbohydrates. This mechanism is called primary production. The pyramid then proceeds through the various trophic levels to the apex predators at the top.

When energy is transferred from one trophic level to the next, typically only ten percent is used to build new biomass. The remaining ninety percent goes to metabolic processes or is dissipated as heat. This energy loss means that productivity pyramids are never inverted, and generally limits food chains to about six levels. However, in oceans, biomass pyramids can be wholly or partially inverted, with more biomass at higher levels.

Terrestrial biomass

Terrestrial biomass generally decreases markedly at each higher trophic level. Examples of terrestrial producers are grasses, trees and scrubs. These have a much higher biomass than the animals that consume them, such as deer, zebras and insects. The level with the least biomass are the highest predators in the food chain, such as foxes and eagles.

In a temperate grassland, grasses and other plants are the primary producers at the bottom of the pyramid. Then come the primary consumers, grasshoppers, voles and bison, followed by the secondary consumers, shrews, hawks and small cats, and finally the tertiary consumers, large cats and wolves. The biomass pyramid is not inverted, and decreases markedly at each higher level.

Ocean biomass

An ocean food web showing a network of food chains

Ocean biomass, in a reversal of terrestrial biomass, can increase at higher trophic levels. In the ocean, the food chain typically starts with phytoplankton, and follows the course:

Phytoplankton → zooplankton → predatory zooplankton → filter feeders → predatory fish

Phytoplankton are the main primary producers at the bottom of the marine food chain. Phytoplankton use photosynthesis to convert inorganic carbon into protoplasm. They are then consumed by microscopic animals called zooplankton.

Zooplankton comprise the second level in the food chain, and include the larva of fish, squid, lobsters and crabs, small crustaceans such as copepods and krill, and many other types.

In turn, smaller zooplankton are consumed both by larger predatory zooplankters, such as krill, and by forage fish, which are small schooling filter feeding fish. This makes up the third level in the food chain.

The fourth trophic level consists of predatory fish, marine mammals, and seabirds which consume forage fish. Examples are swordfish, seals and gannets.

Apex predators, such as orcas which can consume seals and shortfin mako sharks which can consume swordfish, make up the fifth trophic level. Baleen whales can consume zooplankton and krill directly, leading to a food chain with only three or four trophic levels.

Marine environments can have inverted biomass pyramids. In particular, the biomass of consumers (copepods, krill, shrimp, forage fish) is larger than the biomass of primary producers. This happens because the ocean primary producers are tiny phytoplankton which grow and reproduce rapidly, so a small mass can have have a fast rate of primary production. In contrast, terrestrial primary producers are plants which grow and reproduce slowly.

Global biomass

Antarctic krill comprise about 0.7% of the Earth's biomass, the highest of any single animal species.[2]
As a group, copepods form the largest animal biomass on earth.

The most successful animal species, in terms of biomass, is probably the Antarctic krill, Euphausia superba, with a biomass of about 500 million tonnes.[2][3] However, as a group, the small aquatic crustaceans called copepods form the largest animal biomass on earth.[4]

Species individual count average living weight of individual in kg percent biomass (dried) total number of carbon atoms overall biomass in million tonnes
crops 2,000
Antarctic krill (wet) 500
Humans 6.7 billion 50 kg 30% 6.7 x 109 x 5x1026 [5] 100
Copepod (Plankton) 10-6 - 10−9 kg
Cattle 1.3 billion 400 kg 30% 156
Sheep and Goats 1.75 billion [6] 60 kg 30% 31.5
Chickens 24 billion 2 kg 30% 14.4
Ants 107 - 108 billion [7] 3 x 10−4kg
(0.3 grams)
30% 900-9,000
Marine fish 800-2,000[8]

Humans comprise about 100 million tonnes of the Earth's biomass[9], domesticated animals about 700 million tonnes, and crops about 2 billion tonnes.[citation needed] The total biomass of bacteria is estimated to equal that of plants.[10] A 2009 paper in Science estimates, for the first time, the total world fish biomass as somewhere between 0.8 and 2.0 billion tonnes.[11][12] The total global biomass has been estimated to be 2000 billion tonnes with 1600 billion of those tonnes in forests.[13][14]

Net primary production is the rate at which biomass is generated in a given area, mainly due to photosynthesis. Some global producers of biomass in order of productivity rates are

Global primary production can be estimated from satellite observations. Satellites scan the normalised difference vegetation index (NDVI) over terrestrial habitats, and scan sea-surface chlorophyll levels over oceans. This results in 56.4 billion tonnes C/yr (53.8%), for terrestrial primary production, and 48.5 billion tonnes C/yr for oceanic primary production.[18]. Thus, the total photoautotrophic primary production for the Earth is about 104.9 billion tonnes C/yr. This translates to about 426 gC/m²/yr for land production (excluding areas with permanent ice cover), and 140 gC/m²/yr for the oceans.

However, there is a much more significant difference in standing stocks—while accounting for almost half of total annual production, oceanic autotrophs account for only about 0.2% of the total biomass. Autotrophs may have the highest global proportion of biomass, but they are closely rivaled or surpassed by microbes.[19][20]

See also

Notes

  1. ^ International Union of Pure and Applied Chemistry. "biomass". Compendium of Chemical Terminology Internet edition.
  2. ^ a b Nicol, S., Endo, Y. (1997). Fisheries Technical Paper 367: Krill Fisheries of the World. FAO. http://www.fao.org/documents/show_cdr.asp?url_file=//DOCREP/003/W5911E/w5911e00.htm. 
  3. ^ Ross, R. M. and Quetin, L. B. (1988). Euphausia superba: a critical review of annual production. Comp. Biochem. Physiol. 90B, 499-505.
  4. ^ Biology of Copepods at Carl von Ossietzky University of Oldenburg
  5. ^ Freitas, Robert A. Jr.Nanomedicine 3.1 Human Body Chemical Composition Foresight Institute, 1998
  6. ^ World's Rangelands Deteriorating Under Mounting Pressure Earth Policy Institute 2002
  7. ^ Embery, Joan; Lucaire, Ed Collection of Amazing Animal Facts. 1983.
  8. ^ Wilson RW, Millero FJ, Taylor JR, Walsh PJ, Christensen V, Jennings S and Grosell M (2009) "Contribution of Fish to the Marine Inorganic Carbon Cycle" Science, 323 (5912) 359-362. (This article provides a first estimate of global fish biomass)
  9. ^ The world human population was 6.6 billion in January 2008. At an average weight of 100 pounds (30 lbs of biomass), that equals 100 million tonnes.
  10. ^ Whitman, Coleman, and Wiebe, Prokaryotes: The unseen majority, Proc. Natl. Acad. Sci. USA, Vol. 95, pp. 6578–6583, June 1998
  11. ^ Wilson RW, Millero FJ, Taylor JR, Walsh PJ, Christensen V, Jennings S, Grosell M (2009) "Contribution of Fish to the Marine Inorganic Carbon Cycle" Science, 323 (5912) 359-362.
  12. ^ Researcher gives first-ever estimate of worldwide fish biomass and impact on climate change PhysOrg.com, 15 January 2009.
  13. ^ "Biomass Basic Information". http://energy.saving.nu/biomass/basics.shtml. 
  14. ^ "Biomass". http://www.seps.sk/zp/fond/dieret/biomass.htm. 
  15. ^ a b c d e f g Ricklefs, Robert E.; Miller, Gary Leon (2,000). Ecology (4th ed.). Macmillan. p. 192. ISBN 9780716728290. http://books.google.com/books?id=6TMvdZQiySoC&pg=PA192&dq=temperate+forest+ecology+%22net+primary+production%22&lr=&cd=13#v=onepage&q=&f=false. 
  16. ^ Ricklefs, Robert E.; Miller, Gary Leon (2000). Ecology (4th ed.). Macmillan. p. 197. ISBN 9780716728290. http://books.google.com/books?id=6TMvdZQiySoC&pg=PA197&dq=primary+production+biomass+g+m+yr&cd=6#v=onepage&q=primary%20production%20biomass%20g%20m%20yr&f=false. 
  17. ^ a b c d Park, Chris C. (2001). The environment: principles and applications (2nd ed.). Routledge. p. 564. ISBN 9780415217705. http://books.google.com/books?id=Ew3MBjbw4OAC&pg=PA564&dq=primary+productivity+desert&lr=&cd=19#v=onepage&q=primary%20productivity%20desert&f=false. 
  18. ^ Field, C.B.; Behrenfeld, M.J., Randerson, J.T. and Falkowski, P. (1998). "Primary production of the Biosphere: Integrating Terrestrial and Oceanic Components". Science 281: 237–240. 
  19. ^ Whitman, W. B.; Coleman, D. C.; Wieb, W. J. (1998). "Prokaryotes: The unseen majority". Proc. Natl. Acad. Sci. USA 95: 6578–6583. http://www.pnas.org/content/95/12/6578.full.pdf. 
  20. ^ Groombridge, B.; Jenkins, M. (2002), World atlas of biodiversity: earth's living resources in the 21st century, World Conservation Monitoring Centre, United Nations Environment Programme, ISBN 0-520-23688-8, http://books.google.ca/books?id=_kHeAXV5-XwC&printsec=frontcover&source=gbs_navlinks_s#v=onepage&q=biomass&f=false 

References

External links


Simple English

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In ecology, biomass means the cumulation of living matter. That is, it is the total living biological material in a given area or of a biological community or group. Biomass is measured by weight, or by dry weight, per given area (usually measured per square metre or square kilometre).

The most successful animal, in terms of biomass, is the Antarctic krill, Euphausia superba, with a biomass of probably over 500 million tons, roughly twice the total biomass of humans. Biomass may also be a measure of the dried organic mass of an ecosystem.

References


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