The sun is practically the only source of all energy on Earth. However, not all of the energy from solar radiation can be absorbed and used by organisms. Only about half of the usual luminous flux falling on green plants (i.e., on producers) is absorbed by photosynthetic elements, and only a small fraction of the absorbed energy (from 1 to 5%) is stored in the form of biochemical energy (or the energy of chemical bonds) – energy enclosed in plant tissues.
Most of the solar energy is lost as heat.
When energy moves along the food chain from one level to another, the rate of its flow (that is, the amount of energy that has passed from one trophic level to another per unit of time) sharply decreases.
The reasons for the decrease in the amount of energy during the transition from one trophic level to another:
part of the energy contained in food is lost in the process of biochemical transformation of food.
Part of the energy is not absorbed at all and is excreted from the body with excrement, and then decomposed by destructors.
Predators eat only some of the organisms of the previous trophic level, which means that not all of their energy is transferred to the next level.
Some of the energy is lost as heat during breathing.
A large amount of energy is expended in moving animals. This also generates heat.
Energy losses during the transition from one level of the food chain to another (higher) determine the number of these levels and the ratio of the number of predators and prey.
It is estimated that any trophic level receives only about 10% (or slightly more) of the energy of the previous level. This pattern is known as a rule of 10%.
The 10% rule (R. Lindemann’s rule): for each next, higher trophic level, on average, about 10% of the energy of the previous one passes, 90% is lost.
This can be graphically depicted as a pyramid of energy.
The energy pyramid is the ratio between the amount of energy contained in each of the trophic levels.
Due to the high energy loss, the number of trophic levels in a community rarely exceeds three or four.