energetic barriers of ecological systems ken locey
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Energetic barriers of Ecological Systems
Ken Locey
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Metabolic Theory of Ecology MTE
• Ecological phenomena are fundamentally influenced by metabolic rate– rates of development, population increase, times
to extinction, variations in lifespan and elevational diversity, nutrient cycling…
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Metabolic Theory of Ecology MTE
• Ecological phenomena are fundamentally influenced by metabolic rate
• Metabolic rate is fundamentally influenced by mass and temperature– Scaling relationships based on mass• I = ioM3/4
– Exponential effect of temperature on metabolic rate • Boltzmann factor: e-E/kt
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I = ioM3/4e-E/kt
M3/4 : based in delivery resources through fractal-like networks
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I = ioM3/4e-E/kt
• Boltzmann factor, e-E/kt based in the chemical kinetics of biochemical reactions
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Boltzmann factor, e-E/kT
• Increased temp. increases the fraction of molecules with sufficient energy
• Effect on reaction rate is exponential
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Activation Energy, EA
• In MTE, EA is: – activation energy of metabolism• Energy required to undergo cellular respiration, to drive
the tricarboxylic acid cycle, reduce S,N, CH3, etc.
– Suggested to be constant and narrowly constrained ( 0.6 to 0.8, Brown et al. 2004) • Considerable variation
– (0.2-1.2 eV, Munch and Salinas 2009)
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Clarke, Functional Ecology, 2006 Wang et al (2009) PNAs
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McCain and Sanders (2010) Ecology Algar et al. (2007) Global Ecol. Biogeogr.
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Activation Energy
• Determines the rate of biochemical processes
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Activation Energy
• Determines the rate of biochemical processes• Biological systems have evolved to decrease EA
– General evolution of enzymes– Evolution of enzymes specific to cold climates
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Question
• Do changes in activation energy at the biochemical level resemble changes at the ecological level?
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Prediction
• Higher activation energies (larger barriers) occur at lower rates
Zang et al (2005) J Biol Chem
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Carbon Monoxide from Composting due to Thermal Oxidation of Biomass
Hellebrand and Schade (2006) J Env. Qual.
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Estivation in the land snail Otala lacteaRamnanan and Storey (2006) J Exp. Biol.
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Knorr et al (2005) Nature
Soil Organic Carbon (SOC) Turnover
A strong trend for the more slowly cycling pools to have a higher activation energy
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• Prediction appears to have some support among studies where phenomena are the direct product of metabolism
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Question
• Do the dynamics of activation energy explain the variation in species diversity that appears to contradict MTE?
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Prediction
• Lower richness accompanies higher activation energy (larger barrier)
Zang et al (2005) J Biol Chem
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Allen et al. (2007) Scaling Biodiversity
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Allen et al. (2007) Scaling Biodiversity
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Algar et al. (2007) Global Ecol. Biogeogr.
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Want et al. (2009) PNAS
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McCain and Sanders (2010) Ecology
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Boltzmann factor Arrhenius equation f = e-E/kT k = Aoe-E/RT
Gibbs free energy of activation, ∆G‡ k = kBT/h*e-∆G‡/RT
∆G‡ = ∆H‡ - T∆S‡
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Mikan et al (2002) Soil Biology and Biochemistry
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Mikan et al (2002) Soil Biology and Biochemistry
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Algar et al. (2007) Global Ecol. Biogeogr.
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• Prediction is supported among studies where the phenomenon under study is the direct product of metabolism
• Prediction appears to be supported when the phenomenon is fundamentally influenced by metabolic rate.
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Activation energy as an energetic barrier to ecological change
1/kT
ln (R
ate)
EAEA
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EA
EA
Pote
ntial
Ene
rgy COLD
HOT
EA EA
ATP Synthesis ATP Synthesis
Thermal Adaptation
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EA
EA
Pote
ntial
Ene
rgy
EA’
EA’
COLD
HOT
Thermal Adaptation
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Activation energy of metabolism as a structuring force of diversity
1/kT
ln (R
ichn
ess)
EAEA
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Irlich et al (2009) Am Nat.
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Activation energy of metabolism as a structuring force of diversity
1/kT
ln (R
ichn
ess)
EAEA
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Activation energy of metabolism as a structuring force of diversity
1/kT
ln (R
ichn
ess)
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