Flow of energy through a food chain. As energy passes to a higher tropic level, approximately 90% of the useful energy is lost. High tropic levels contain less energy and fewer organisms than lower levels.
At each tropic level in a food chain, energy is used by the
organisms at that level to maintain their own life process. Because
of the 2nd law of energy, some energy is lost to the surroundings
as heat. it is estimated that in going from one tropic level
to the next, about 90 % of the energy is lost.
In moving to the next tropic level, only 10 % of the original energy is available. By the third tropic level only 1% of the energy is available.
Food Supply - Eat grain rather than Meat
Energy is used much more efficiently if humans eat plants (first tropic level) instead of meat (second tropic level. A given area of farmland can support more people if the crops are fed directly to people rather than to livestock that people then eat.
For example if a man needs 3,000 Calories per day, then 30,000 Cal beef are needed, which in turn need 300,000 Cal of corn, which in turn means 30,000,000 Cal of sunshine. This works out to be 1.5 acres of corn per day per person. If the person ate corn directly then 10 people could be supported by the same 1.5 acres of corn.