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In general, only 10% of the energy at one trophic level
is passed on to the next level.
Ninety percent of energy is lost to the environment.
For instance, 1000 kilograms of producers in level T1
can support 100 kilograms of primary consumers,
10 kilograms of secondary consumers,
and only 1 kilogram of tertiary consumers.
That means for every 1 kilogram of hawk in an ecosystem
there must be 1000 kilograms of producers!
This is known as the 10% rule.
The 10% rule also helps you calculate how much energy
is available at a given level of the energy pyramid.
If you know how much energy is available at one level,
as measured by kilocalories, or kcal, you can predict how much energy
is available at every other level in the energy pyramid
by using the same technique we just applied.
For instance,
if 100,000 kilocalories are available at trophic level 1,
then 10,000 kilocalories are available at level 2.
You can calculate how many kilocalories will be available
at trophic level 3 by dividing the energy at level 2 by 10.
Divide the energy available at level 2
by 10 to determine the energy available at level 3.
Then, to calculate the energy available at T4,
divide 1000 by 10.
One hundred kilocalories are available at level T4.