There are many different cycles within communities of organisms, but there are also cycles within the abiotic, or non-living components of ecosystems.
Energy flows through the ecosystem. First energy is captured by the producers, those plants and microorganisms that can produce their own food by photosynthesis; then the energy passes along the food chain to consumers, such as herbivores, carnivores, and decomposers.
All of these different feeding levels, or trophic levels as they are called, form a type of energy pyramid in ecosystems. As the energy passes from level to level, less and less usable energy is available to organisms at the higher levels.
Biologists estimate that on average only 10% of the plant’s accumulated energy is passed on to the body of the organism that eats it. Where does the rest go? Some is used for digestion, work, growth, and reproduction but only about 10% remains in the tissue of the animal that ate it. The rest of the energy is dissipated as heat.
When the energy is passed to the next trophic level, for example from the herbivore that eats the plant to the carnivore that eats it, the energy that is retained again is reduced to 10% and the rest is not available. At each trophic level there is a decrease of about 90% of the energy available.
Despite this reduction in energy the ecosystem is sustainable because the number of organisms or biomass at each trophic level is also reduced by at least 90%. The biomass at the bottom level is so great and replenishes itself so quickly it can sustain the organisms at the higher levels.