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Thermodynamics, man and biosphere

This is the summer time 2017 main message of the Michel Serres Institute. Take it as a free exercise during vacation time, a kind of homework to keep your mind pro-active. Have a look at the sketch, is a problem-solving exercise. Explanations are given in support to help you find solutions.
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Solving the problem – support information

Photosynthesis and biomass production : land, water, yield

Biological resources are life generated materials and processes which are naturally and sustainably renewable and biodegradable. As such, biological resources fulfil man’s essential, fundamental needs : food, feed, bioactive molecules, fuel, shelter, fibre, bio-remediation etc. They play a key role in present and future socio-economic evolutions (also see Knowledge-based bio-economy concept, KBBE).
Only the Net Primary Production is available for consumption, and is the basis of all food chains that support species biodiversity.
Genetic yield potential (Y) : the yield that a crop can attain through photosynthesis under optimal management practices and in the absence of biotic and abiotic stresses.
Factors of Y :
St (GJ m−2) : the total incident solar radiation across the growing season.
partitioning efficiency (εp), also termed harvest index ; the amount of the total biomass energy partitioned into the harvested portion of the crop.
light interception efficiency (εi) of photosynthetically active radiation (400–700 nm) is determined by the speed of canopy development and closure, leaf absorbance, canopy longevity, size, and architecture.
conversion efficiency (εc) the ratio of biomass energy produced over a given period to the radiative energy intercepted by the canopy over the same period (i.e. the combined gross photosynthesis of all leaves within the canopy, less all plant respiratory losses).

Zhu XG, Long SP, Ort DR : Improving photosynthetic efficiency for greater yield. Annual Review of Plant Biology 2010, 61:235-261.

Ecological footprint : A measure of how much biologically productive land and water an individual, population or activity require to produce all the resources it consumes and to absorb the waste it generates using prevailing technology and resource management practices. Today humanity uses the equivalent of 1.5 planets to provide the resources we use and absorb our waste.
Ecological deficit  : the difference between the biocapacity and ecological footprint of a region or country. An ecological deficit occurs when the Footprint of a population exceeds the biocapacity of the area available to that population.
Ecological reserve  : an ecological reserve exists when the biocapacity of a region exceeds its population’s Footprint. Also consider terms as biodiversity buffer / ecosystem buffer : the amount of biocapacity set aside to maintain representative ecosystem types and viable populations of species (related to resilience of ecosystems).

Global Footprint Network - World Footprint, Do we fit on the planet ? []

Food chains, biological efficiency, and carrying capacity

A food chain or a food web defines who is eaten by whom in a given ecosystem.
Food chains / webs are important in understanding productivity issues because they operate through biomass production at various trophic levels and ultimately define ecological efficiency.
Ecological efficiency is the efficiency with which production at one trophic level is converted into production at the next level. This corresponds mainly to assimilation and growth efficiencies.
Assimilation efficiency corresponds to the fraction of food taken up by an organism, and depends on the composition and digestibility of ingested food. Typically being around 80% for zooplankton and fish, for example.
Growth efficiency is expressed as the fraction of ingested food required for growth and approximates 20% in the same organisms. This apparently low bio-efficiency reflects the price of speed and simultaneous regulation of biochemical processes operating at various organization levels, and thus far from thermodynamic equilibrium.
These factors contribute therefore to an overall low ecological efficiency, which has been empirically estimated at 10-20% (the part microbial food loops / webs play in the system is ignored here). It follows that on a scale of 100 units, from primary production down to various trophic levels, the production of herbivores is maximum 10-20, while that of first level carnivores is 1-2, and so on. A trophic chain of 7 in the Norwegian Sea (Flagellates > Ciliates > Oithona > Euchaeta > Themisto > Herring > Salmon) ends up with salmon production of 0.0002 – 0.02 units. Thus, production falls rapidly as we climb the food chain and with long food chains top trophic level production can be as low as 10-5 to 10-8 of the primary production.

Agriculture and human food systems are far out of such scales and thermodynamic rules.
Feed conversion  : In animal husbandry, feed conversion ratio (FCR), feed conversion rate, or feed conversion efficiency (FCE), is a measure of an animal’s efficiency in converting feed mass into increased body mass.
The ratio of the kg of feed needed to produce one kg of life weight (body mass). Examples are : Milk 0.7, Carp 1.5, Egg 3.8, Chicken 2.3, Pork 5.8, Beef 12.7. Only part of the life weight is edible.

The carrying capacity for the top level predators in an ecosystem is very sensitive to the number of steps in the food chains / webs that support it.
The carrying capacity of a biological species in a given environment is the maximum population size of this species that the environment can sustain indefinitely, given the food, habitat, water and other necessities available. If the population size of the species is over its carrying capacity, the environment will be degraded more or less quickly and consequently will not sustain the population, which in turn will decrease. Moreover, if the environment itself has its resources decreasing in reason of an abiotic cause, the carrying capacity will decrease.
Therefore, the condition of the entire ecosystem is at stake when defining harvesting stocks and demographic loads. Long food chains, complex and unstructured food webs are indicators of both resilient ecosystems and rich biodiversity.
Human carrying capacity under business as usual is a real issue ; that remains a political and cultural taboo so far.

Skjoldal HR, Dalpadado P, Dommasnes A : Food webs and trophic interactions. The Norwegain Sea ecosystem Tapir Academic Press, Trondheim 2004, 447:506.

Dorst J : La force du vivant. Flammarion ; 1979.

Blanchard JL, Law R, Castle MD, Jennings S : Coupled energy pathways and the resilience of size-structured food webs. Theoretical Ecology 2010:1-12.

USDA Agricultural Statistics Annual

Feed conversion ratio

Carrying capacity

Global Footprint Network - World Footprint, Do we fit on the planet

Viking laws to illustrate business as usual :
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Illustration : Snorre -

Ioan Negrutiu - Juillet 2017

Publié ou mis à jour le 12 juillet 2017