Primary Production

Everything that happens in an ecosystem depends on the initial importing of energy and nutrients by primary producers. Most systems are supported by photoautotrophs, which convert the radiant energy of the sun into chemical-bond energy. The ability to photo-synthesize stable carbohydrate compounds is found today primarily in three important groups of organisms: blue-green bacteria (also called cyanobacteria) in aquatic environments; algal protists (many different groups), also in aquatic settings; and multicellular plants, chiefly in terrestrial environments but with some representatives in aquatic systems. At thermal vents and chemical seeps in the deep ocean, chemoautotrophic bacteria are the primary producers. Ecosystems that depend on these inputs are said to be autotrophic. Other systems, however, depend on input of organic material from adjacent autotrophic systems. These include rivers that import detritus from upstream locations, lakes that depend on the organic material delivered by runoff and inflow, and especially vast areas of the deep-sea floor that need detritus falling from the upper water column to support life well below the photic zone. These systems are referred to as het-erotrophic.

All ecosystems are open, in the sense that energy in one form or another has to be imported from the outside; and all systems maintain organization and support their own development through time with inputs of energy and chemicals. Most of this activity can be summarized in two equations. Energy transfer is represented by: Pg = Pn + R, where Pg is gross productivity, Pn is net productivity, and R is respiration (an expression of the first law of thermodynamics as it applies in an ecosystem, either in terms of initially importing and transforming energy or in terms of passing the energy to higher levels in the system). The available energy present at any position in a food web at any given time is: AB = Pg - R - H - D, where B is biomass, Pg is gross production, R is respiration, H is the rate of harvest, and D is the mortality rate. Because of losses inherent in transforming radiant energy into chemical compounds and in transferring this material through processors at different organizational levels, energy flow is not very efficient, and only a limited number of tiers in a food pyramid or steps in a food chain are allowed to develop (usually < 5), although an enormous amount of variation in trophic structure has been observed.

Worm Farming

Worm Farming

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