Ecology

Less than 1% of the solar energy reaching Earth's surface is absorbed by green plants or algae and used in photosynthesis. However, this fixed solar energy is the energetic basis of the structure and function of ecosystems. The total fixation of energy by plants is known as gross primary production (GPP). Some of that fixed energy is used by plants to support their own metabolic demands, or respiration (R). The quantity of energy that is left over (that is, GPP MINUS R) is known as net primary production (NPP). If NPP has a positive value, then plant biomass accumulates over time, and is available to support the energy requirements of herbivorous animals, which are themselves available as food to support to carnivores. Any plant or animal biomass that is not directly consumed eventually dies, and is consumed by decomposers (or detritivores), the most important of which are microorganisms such as bacteria and fungi. The complex of ecological relationships among all of the plants, animals, and decomposers is known as a food web.