The ecological pyramid rule is a law describing the hierarchical structure of energy or biomass transfer between trophic levels in an ecosystem.The ecological pyramid rule, or the ten percent rule, was formulated by Raymond Lindeman in 1942. Studying a lake ecosystem, he found that when energy is transferred from one trophic level to another (from plants to herbivores, from herbivores to predators), its amount decreases approximately tenfold. The remaining 90 percent is dissipated as heat or used for the organisms' life activities. This limitation imposes strict constraints on the length of food chains: rarely can one find more than four or five links. The pyramid can be not only energetic but also numerical (the number of individuals decreases toward the top) or biomass-based (the total mass of organisms decreases). However, in aquatic ecosystems, an inverted biomass pyramid is sometimes observed: phytoplankton reproduces quickly and is consumed, so its mass at a given moment may be less than the mass of zooplankton, but the energy flow still follows the rule.
The concept of trophic levels and energy transfer in ecosystems was developed in the works of Charles Elton in the 1920s, but the rule received quantitative expression thanks to Raymond Lindeman. In 1942, he published the article 'The Trophic-Dynamic Aspect of Ecology', where, based on the study of Cedar Bog Lake (Minnesota), he showed that the efficiency of energy transfer between levels averages 10%. Lindeman tragically died shortly after publication, but his work became a cornerstone of ecosystem ecology. Later, the rule was refined: in different ecosystems, efficiency can vary from 5 to 20%, but the order of magnitude remains unchanged.
The rule is applied in agriculture to calculate feed rations and assess pasture productivity, in fisheries to determine catch quotas considering population recovery, and in ecological modeling to predict the consequences of changes in species numbers. Limits of applicability: the rule is averaged; in specific food chains, efficiency may differ; it does not account for detrital chains (decomposition of dead organic matter), where energy losses are different. In aquatic ecosystems, biomass may not follow a pyramidal shape due to the high turnover rate of phytoplankton.
The rule explains why predators are always fewer than herbivores and why large animals need vast territories. Calculations of allowable fish catch and livestock feeding rates are based on this.
To feed one person who eats only meat, ten times more pasture is required than for a vegetarian. This is a direct consequence of the ten percent rule.



