Trophic efficiency the percentage of production

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Trophic efficiency – the percentage of production transferred from one trophic level to the next. Trophic efficiencies are always lower than production efficiencies and only range about 5 – 20 %. Trophic efficiency is expressed in three ways: o Pyramids of production – shows the loss of energy on each trophic level where primary producers always form the base of the pyramid o Pyramids of biomass each tier represents the total dry weight of all organisms in one trophic level – Most biomass pyramids narrow sharply as we move up to the top-level carnivores, however, some aquatic ecosystems have inverted biomass pyramids because of the short turnover time of phytoplankton. o
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o Pyramid of numbers – shows the number of organisms on each trophic level: The dynamics of energy flow has serious implications on the human population as well. More people can be fed efficiently with grains and vegetables than with meat. IV. BIOGEOCHEMICAL CYCLES Chemical elements only available in limited amounts in ecosystems so these essential elements must be recycled between the biotic and abiotic environment – biogeochemical cycles The general model of these cycles is shown below:
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The following four cycles are the most studied and most important for living organisms: Water Cycle o Water is essential to all organisms and its availability influences the rate of ecosystem processes, especially the primary production and decomposition o Forms available: Mostly liquid water o Reservoirs: The oceans (97%), glaciers and polar ice caps (2%), lakes, rivers, groundwater (1%), atmosphere (negligible) o Key processes: evaporation of liquid water by solar energy, condensation of water vapor into clouds and precipitation, transpiration by terrestrial plants Carbon Cycle o Carbon is the main element in every organic compound o Forms available to life: Primary consumers convert CO 2 into organic molecules o Reservoirs: fossil fuels, soil, sediments, dissolved carbon compounds in the oceans, organisms’ biomass, atmosphere, sedimentary rocks (slow turn over) o Key processes: photosynthesis, cellular respiration, volcanoes, burning fossil fuels
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Nitrogen Cycle o Component of amino acids (proteins) and nucleic acids o Forms available for life: Plants and algae can utilize ammonium (NH 4 + ) and
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