74.73.232.36: /* External links */ 404 from j2me-otp link, replaced with link to same content on GitHub

2015-01-04T18:44:19Z

External links: 404 from j2me-otp link, replaced with link to same content on GitHub

46.226.190.244 at 01:23, 24 July 2013

2013-07-24T01:23:13Z

← Older revision		Revision as of 03:23, 24 July 2013
Line 1:		Line 1:
	~~Anybody who wrote~~ the ~~blog~~ is ~~called Eusebio~~. ~~South Carolina~~ is its ~~birth place~~. The ~~most beloved hobby~~ for ~~him~~ and as ~~well his kids~~ is to ~~fish~~ and he'~~s previously~~ been ~~doing it~~ for a long ~~time~~. ~~Filing~~ has been ~~his profession~~ as ~~news got around~~. ~~Go to his website locate out more~~: ~~http~~://~~circuspartypanama~~.~~com~~<br><br>~~Also visit my web blog~~ - ~~[http:~~//~~circuspartypanama~~.~~com clash~~ of ~~clans hack~~]		The '''metabolic theory of ecology''' (MTE) is an extension of [[Kleiber's law]] and posits that the [[Basal metabolic rate\|metabolic rate]] of organisms is the fundamental biological rate that governs most observed patterns in ecology.<ref name="Brown04">{{cite journal \|author=Brown, J. H., Gillooly, J. F., Allen, A. P., Savage, V. M., & G. B. West \|title=Toward a metabolic theory of ecology \|journal=Ecology \|volume=85 \|issue=7 \|pages=1771–89 \|year=2004 \|doi=10.1890/03-9000
			}}</ref>

			MTE is based on an interpretation of the relationships between body size, body temperature, and [[Metabolism\|metabolic rate]] across all organisms. Small-bodied organisms tend to have higher mass-specific metabolic rates than larger-bodied organisms. Furthermore, organisms that operate at warm temperatures through [[Warm-blooded\|endothermy]] or by living in warm environments tend towards higher metabolic rates than organisms that operate at colder temperatures. This pattern is consistent from the unicellular level up to the level of the largest animals on the planet.

			In MTE, this relationship is considered to be the single constraint that defines biological processes at all levels of organization (from individual up to ecosystem level), and is a [[Macroecology\|macroecological]] theory that aims to be universal in scope and application.<ref name="Brown04"/>

			== Theoretical background ==

			Metabolic rate scales with the mass of an organism of a given species according to [[Kleiber's law]] where ''B'' is whole organism metabolic rate (in watts or other unit of power), ''M'' is organism mass (in kg), and ''B''<sub>o</sub> is a mass-independent normalization constant (given in a unit of power divided by a unit of mass. In this case, watts per kilogram):

			:<math>B = B_oM ^ {3/4}\,</math>

			At increased temperatures, chemical reactions proceed faster. This relationship is described by the [[Boltzmann factor]], where ''E'' is [[activation energy]] in [[electronvolt]]s or [[joule]]s, ''t'' is absolute temperature in kelvins, and ''k'' is the [[Boltzmann constant]] in eV/K or J/K:

			:<math>e^{-\frac{E}{k\,t}}</math>

			While ''B''<sub>o</sub> in the previous equation is mass-independent, it is not explicitly independent of temperature. To explain the relationship between body mass and temperature, these two equations are combined to produce the primary equation of the MTE, where ''b''<sub>o</sub> is a normalization constant that is independent of body size or temperature:

			:<math>B = b_oM^{3/4}e^{-\frac{E}{k\,t}}</math>

			According to this relationship, metabolic rate is a function of an organism’s body mass and body temperature. By this equation, large organisms have proportionally higher metabolic rates (in Watts) than small organisms, and organisms at high body temperatures have higher metabolic rates than those that exist at low body temperatures.However specific metabolic rate (SMR, in Watts/kg) is given by

			<math>SMR = (B/M) = b_oM^{-1/4}e^{-\frac{E}{k\,t}}</math>

			Hence SMR for large organisms are lower than small organisms.

			== Controversy over exponent ==

			There is disagreement amongst researchers about the most accurate value for use in the power function, and whether the factor is indeed universal.<ref name="Agutter04">{{cite journal \|author=Agutter, P.S., Wheatley, D.N. \|title=Metabolic scaling: consensus or controversy? \|journal=Theoretical biology and medical modelling \|volume=1 \|issue= \|pages=13 \|year=2004 \|doi=10.1186/1742-4682-1-13 \|pmid=15546492 \|pmc=539293}}</ref> The main disagreement is whether metabolic rate scales to the power of 3/4 or 2/3. The majority view is currently that 3/4 is the correct exponent, but a large minority believe that 2/3 is the more accurate value.<ref name="Agutter04"/> Although a rigorous exploration of the controversy over choice of scaling factor is beyond the scope of this article, it is informative to understand the biological justification for the use of either value.

			The argument that 2/3 should be the correct scaling factor is based on the assumption that energy dissipation across the surface area of three dimensional organisms is the key factor driving the relationship between metabolic rate and body size.<ref name="Agutter04"/> Smaller organisms tend to have higher surface area to volume ratios, causing them to lose heat energy at a faster rate than large organisms. As a consequence, small organisms must have higher specific metabolic rates to combat this loss of energy over their large surface area to volume ratio.

			In contrast, the argument for a 3/4 scaling factor is based on a hydraulic model of energy distribution in organisms, where the primary source of energy dissipation is across the membranes of internal distribution networks. This model is based on the idea that metabolism is essentially the rate at which an organism’s distribution networks (such as circulatory systems in animals or xylem and phloem in plants) deliver nutrients and energy to body tissues.<ref name="West99">{{cite journal \|author=West, G.B., Brown, J.H., & Enquist, B.J. \|title=The fourth dimension of life: Fractal geometry and allometric scaling of organisms \|journal=Science \|volume=284 \|issue=5420 \|pages=1677–9 \|year=1999 \|pmid=10356399 \|doi=10.1126/science.284.5420.167 }}</ref> It therefore takes longer for large organisms to distribute nutrients throughout the body and thus they have a slower metabolic rate. The 3/4 factor is then derived from the observation that selection favors a [[fractal]] or near-fractal distribution network for space-filling circulatory systems.<ref name="West99"/> All fractal networks terminate in identical units (such as capillary beds), and the number of such units in organisms is proportional to a 3/4 power relationship with body size.<ref name="West99"/>

			Kolokotrones et al. 2010<ref name="Kolokotrones10">{{cite journal \|author=Kolokotrones, T., Van Savage, Deeds, E. J.\|title=Curvature in metabolic scaling \|journal=Nature \|volume=464 \|issue=7289 \|pages=753–756 \|year=2010 \|doi=10.1038/nature08920
			}}</ref> showed that relationship between mass and metabolic rate has a convex curvature on logarithmic scale. The curvature explains the variations in the power law exponent.

			Despite the controversy over the value of the exponent, the implications of this theory might remain true regardless of its precise numerical value.

			== Implications of the theory ==
			The metabolic theory of ecology’s main implication is that metabolic rate, and the influence of body size and temperature on metabolic rate, provide the fundamental constraints by which ecological processes are governed. If this holds true from the level of the individual up to ecosystem level processes, then life history attributes, population dynamics, and ecosystem processes could be explained by the relationship between metabolic rate, body size, and body temperature.

			===Organism level===
			Small animals tend to grow fast, breed early, and die young.<ref name="Savage04">{{cite journal \|author=Savage V.M., Gillooly J.F., Brown J.H., West G.B. & Charnov E.L. \|title=Effects of body size and temperature on population growth \|journal=American Naturalist \|volume=163 \|issue=3 \|pages=429–441 \|year=2004 \|pmid=15026978 \|doi=10.1086/381872 }}</ref> According to MTE, these patterns in [[Life history theory\|life history]] traits are constrained by metabolism. An organism's metabolic rate determines its rate of food consumption, which in turn determines its rate of growth. This increased growth rate produces trade-offs that accelerate [[senescence]]. For example, metabolic processes produce [[Radical (chemistry)\|free radicals]] as a by-product of energy production.<ref>{{cite book \|editor=Enrique Cadenas, Lester Packer \|title=Understanding the process of ages : the roles of mitochondria, free radicals, and antioxidants \|publisher=Marcel Dekker \|location=New York \|year=1999 \|isbn=0-8247-1723-6 }}</ref> These in turn cause damage at the cellular level, which promotes senescence and ultimately death. Selection favors organisms which best propagate given these constraints. As a result, smaller, shorter lived organisms tend to reproduce earlier in their life histories.

			===Population and community level===
			MTE has profound implications for the interpretation of population growth and community diversity.<ref name="Savage04"/> Classically, species are thought of as being either ''r'' selected (where population size is limited by the exponential rate of population growth) or ''K'' selected (where population size is limited by carrying capacity). MTE explains this diversity of reproductive strategies as a consequence of the metabolic constraints of organisms. Small organisms and organisms that exist at high body temperatures tend to be ''r'' selected, which fits with the prediction that ''r'' selection is a consequence of metabolic rate.<ref name="Brown04"/> Conversely, larger and cooler bodied animals tend to be ''K'' selected. The relationship between body size and rate of population growth has been demonstrated empirically,<ref>{{cite journal \|author=Denney N.H., Jennings S. & Reynolds J.D. \|title=Life history correlates of maximum population growth rates in marine fishes \|journal=Proceedings of the Royal Society of London B \|volume=269 \|issue= 1506\|pages=2229–37 \|year=2002 \|doi=10.1098/rspb.2002.2138}}</ref> and in fact has been shown to scale to ''M''<sup>-1/4</sup> across taxonomic groups.<ref name="Savage04"/> The optimal population growth rate for a species is therefore thought to be determined by the allometric constraints outlined by the MTE, rather than strictly as a life history trait that is selected for based on environmental conditions.

			Observed patterns of diversity can be similarly explained by MTE. It has long been observed that there are more small species than large species.<ref>{{cite journal \|author=Hutchinson, G., MacArthur, R. \|title=A theoretical ecological model of size distributions among species of animals \|journal=Am. Nat. \|volume=93 \|issue= 869\|pages=117–125 \|year=1959 \|doi=10.1086/282063}}</ref> In addition, there are more species in the tropics than at higher latitudes.<ref name="Brown04"/> Classically, the latitudinal gradient in species diversity has been explained by factors such as higher productivity or reduced seasonality.<ref>{{cite journal \|author=Rohde, K. \|title=Latitudinal gradients in species-diversity: the search for the primary cause \|jstor=3545569 \|journal=Oikos \|volume=65 \|issue=3 \|pages=514–527 \|year=1992 \|doi=10.2307/3545569}}</ref> In contrast, MTE explains this pattern as being driven by the kinetic constraints imposed by temperature on metabolism.<ref>{{cite journal \|author=Allen A.P., Brown J.H. & Gillooly J.F. \|title=Global biodiversity, biochemical kinetics, and the energetic-equivalence rule \|journal=Science \|volume=297 \|issue=5586 \|pages=1545–8 \|year=2002 \|pmid=12202828 \|doi=10.1126/science.1072380}}</ref> The rate of molecular evolution scales with metabolic rate,<ref>{{cite journal \|author=Gillooly, J.F., Allen, A.P., West, G.B., & Brown, J.H. \|title=The rate of DNA evolution: Effects of body size and temperature on the molecular clock \|journal=Proc Natl Acad Sci U S A. \|volume=102 \|issue=1 \|pages=140–5 \|year=2005 \|pmid=15618408 \|pmc=544068 \|doi=10.1073/pnas.0407735101}}</ref> such that organisms with higher metabolic rates show a higher rate of change at the molecular level.<ref name="Brown04"/> If a higher rate of molecular evolution causes increased speciation rates, then adaptation and ultimately speciation may occur more quickly in warm environments and in small bodied species, ultimately explaining observed [[Body size-species richness\|patterns of diversity across body size]] and latitude.

			MTE’s ability to explain patterns of diversity remains controversial. For example, researchers analyzed patterns of diversity of New World coral snakes to see whether the geographical distribution of species fit within the predictions of MTE (i.e. more species in warmer areas).<ref>{{cite journal \|author=Terribile, L.C., & Diniz-Filho, J.A.F. \|title=Spatial patterns of species richness in New World coral snakes and the metabolic theory of ecology \|journal=Acta oecologica \|volume=35 \|issue= 2\|pages=163–173 \|year=2009 \|doi=10.1016/j.actao.2008.09.006}}</ref> They found that the observed pattern of diversity could not be explained by temperature alone, and that other spatial factors such as primary productivity, topographic heterogeneity, and habitat factors better predicted the observed pattern.

			===Ecosystem processes===
			At the ecosystem level, MTE explains the relationship between temperature and production of biomass. The average production to biomass ratio of organisms is higher in small organisms than large ones.<ref>{{cite journal \|author=Banse K. & Mosher S. \|title=Adult body mass and annual production/biomass relationships of field populations \|jstor=2937256 \|journal=Ecol. Monog. \|volume=50 \|issue=3 \|pages=355–379 \|year=1980 \|doi=10.2307/2937256}}</ref> This relationship is further regulated by temperature, and the rate of production increases with temperature.<ref>{{cite journal \|author=Ernest S.K.M., Enquist B.J., Brown J.H., Charnov E.L., Gillooly J.F., Savage V.M., White E.P., Smith F.A., Hadly E.A., Haskell J.P., Lyons S.K., Maurer B.A., Niklas K.J. & Tiffney B. \|title=Thermodynamic and metabolic effects on the scaling of production and population energy use \|journal=Ecology Letters \|volume=6 \|issue= 11\|pages=990–5 \|year=2003 \|doi=10.1046/j.1461-0248.2003.00526.x}}</ref> As production consistently scales with body mass, MTE predicts that the primary factor that causes differing rates of production between ecosystems is temperature and not the mass of organisms within the ecosystem.<ref name="Brown04"/> This suggests that regions with similar climatic factors would sustain the same primary production, even if standing biomass is different.<ref name="Brown04"/>

			== See also ==
			* [[Allometry]]
			* [[Constructal theory]]
			* [[Dynamic energy budget]]
			* [[Ecology]]
			* [[Evolutionary physiology]]
			* [[Occupancy-abundance relationship]]

			== References ==
			{{reflist\|2}}

			{{modelling ecosystems}}

			{{DEFAULTSORT:Metabolic Theory Of Ecology}}
			[[Category:Ecological theories]]

174.25.100.86: /* Authentication */ not necessarily printed out on paper

2012-08-15T05:11:21Z

Authentication: not necessarily printed out on paper

New page

Anybody who wrote the blog is called Eusebio. South Carolina is its birth place. The most beloved hobby for him and as well his kids is to fish and he's previously been doing it for a long time. Filing has been his profession as news got around. Go to his website locate out more: http://circuspartypanama.com<br><br>Also visit my web blog - [http://circuspartypanama.com clash of clans hack]

S/KEY - Revision history

74.73.232.36: /* External links */ 404 from j2me-otp link, replaced with link to same content on GitHub

46.226.190.244 at 01:23, 24 July 2013

174.25.100.86: /* Authentication */ not necessarily printed out on paper