Feed conversion efficiency
Energy transfer between trophic levels is a difficult thing to calculate in a real food web, but the theory is very simple.
All trophic levels, besides the primary producers, consume some other living organisms. The consumed energy, in the form of biomass, is either used for metabolism, growth or ends up as feces.
Only the energy used for growth will have an impact on the energy transferred between levels of the food web.
Subtracting the energy contained in the feces and the energy used for the metabolism from the total ingested energy, will result in the percentage of the ingested energy made into new biomass.
The biomass can then be consumed by other organisms. If this is the case, then the same calculation can be performed.
Consequently, to calculate the biomass which will be transferred over several trophic levels of the food web, we can multiply the percentage of the transferred energy at each level.
An example of a food chain:
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The first level is 30% efficient.
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The second level is 50% efficient.
If 100 kg of biomass is going through the first and second level we will therefore get a final biomass of: