Energetic barriers of Ecological Systems

Ken Locey

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…

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

I = ioM3/4e-E/kt

M3/4 : based in delivery resources through fractal-like networks

I = ioM3/4e-E/kt

• Boltzmann factor, e-E/kt based in the chemical kinetics of biochemical reactions

Boltzmann factor, e-E/kT

• Increased temp. increases the fraction of molecules with sufficient energy

• Effect on reaction rate is exponential

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)

Clarke, Functional Ecology, 2006 Wang et al (2009) PNAs

McCain and Sanders (2010) Ecology Algar et al. (2007) Global Ecol. Biogeogr.

Activation Energy

• Determines the rate of biochemical processes

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

Question

• Do changes in activation energy at the biochemical level resemble changes at the ecological level?

Prediction

• Higher activation energies (larger barriers) occur at lower rates

Zang et al (2005) J Biol Chem

Carbon Monoxide from Composting due to Thermal Oxidation of Biomass

Hellebrand and Schade (2006) J Env. Qual.

Estivation in the land snail Otala lacteaRamnanan and Storey (2006) J Exp. Biol.

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

• Prediction appears to have some support among studies where phenomena are the direct product of metabolism

Question

• Do the dynamics of activation energy explain the variation in species diversity that appears to contradict MTE?

Prediction

• Lower richness accompanies higher activation energy (larger barrier)

Zang et al (2005) J Biol Chem

Allen et al. (2007) Scaling Biodiversity

Allen et al. (2007) Scaling Biodiversity

Algar et al. (2007) Global Ecol. Biogeogr.

Want et al. (2009) PNAS

McCain and Sanders (2010) Ecology

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‡

Mikan et al (2002) Soil Biology and Biochemistry

Mikan et al (2002) Soil Biology and Biochemistry

Algar et al. (2007) Global Ecol. Biogeogr.

• 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.

Activation energy as an energetic barrier to ecological change

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Activation energy of metabolism as a structuring force of diversity

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Irlich et al (2009) Am Nat.

Activation energy of metabolism as a structuring force of diversity

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Activation energy of metabolism as a structuring force of diversity

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