The 10% rule states that 10% of the energy stored as biomass at one trophic level, ends up as biomass at the next trophic level. So, in a 4 levels food web, we need 1000 kg of the first level -phytoplankton- to produce 1 kg of the last level -large fishes-.
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From the energy that reaches the earth's surface, only 0.1 or 1% is absorbed by autotroph organisms or producers. This small percentage of this energy flows through all organisms in the ecosystem -from autotrophs to heterotrophs- until it dissipates in the environment.
Only 10% of energy is tranferred from one level to the next one. This assessment is called The 10% rule. It states that only about 10% of the energy stored as biomass at one trophic level, ends up as biomass at the next trophic level.
The progressive reduction of energy determines the number of trophic levels (4 or 5).
Let us analyze the given example.
Phytoplankton ⇒ Zooplankton ⇒ Small Fishes ⇒ Large Fishes
According to the 10% rule, to support 1 kg of large fish, 10 kg of the anterior level -small fish- is needed.
To get the biomass of each level needed to support 1 kg of large fish, we need to multiply each level biomass by 10. This is:
So, in this example, to produce 1 Kg of large fishes, we need 10 kg of small fishes, 100 kg of zooplankton, and 1000Kg of phytoplankton.
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