Trophic dynamics

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In ecology, trophic dynamics is the system of trophic levels (Greek τροφή, trophē, food or feeding), which describes the position that an organism occupies in a food chain: what an organism eats, and what eats the organism.

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Energy economy

Ecologists study the energy economies of natural systems. Foundation species (also known as primary producers) harvest an energy source such as sunlight and turn it into biomass by fixing carbon dioxide. Organic compounds such as carbohydrates, fats, and proteins are high-energy substances consumed by other organisms (primary consumers), which are in turn consumed by others. Each link in this chain of consumption is termed a trophic level. Because only a fraction of the energy used by a level is converted to biomass, less energy is available at higher levels. Plants, algae, and some bacteria can perform photosynthesis and combine water and carbon dioxide to make organic compounds using the Sun's energy.

Most ecosystems ultimately rely upon the Sun for energy and upon autotrophs to fix carbon and harness that energy. There are only a few exceptions to this, such as chemosynthetic archaea and bacteria, which derive energy from the breakdown of sulfur compounds such as hydrogen sulfide around deep sea hydrothermal vents and acid mine drainage. These organisms can utilize hydrogen sulfide in lieu of water to make organic compounds, and as the reaction between hydrogen sulfide and carbon dioxide is a spontaneous one, they do not need energy from sunlight. Lithotrophs can use inorganic compounds as electron donors to manufacture organic compounds or produce ATP. Sulfur-oxidizing bacteria, for example, can consume hydrogen sulfide, elemental sulfur, sulfite, and thiosulfate as energy sources instead of carbohydrates, fats, and proteins. Using sulfite oxidase, sulfur-oxidizing bacteria can obtain electrons from sulfur compounds and form ATP through an electron transport chain (ETC).

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