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“All flesh is grass” -Isaiah 40:6 Three hundred trout are needed to support one man for a year. The trout, in turn, must consume 90,000 frogs, that must consume 27 million grasshoppers that live off of 1,000 tons of grass. ++++++++++++++++++++++++++ -- G. Tyler Miller, Jr., American Chemist (1971) +++++++++++++++++ Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Energy Flow and Geochemical Cycling in an Ecosystem Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Regardless of an ecosystem’s size, its dynamics involve two main processes: energy flow and chemical cycling • Energy flows through ecosystems while matter cycles within them Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Conservation of Energy – The first law of thermodynamics • States that energy cannot be created or destroyed, only transformed • Energy enters an ecosystem as solar radiation, is conserved, and is lost from organisms as heat Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • The second law of thermodynamics states that every exchange of energy increases the entropy of the universe • Entropy is commonly understood as a measure of molecular disorder within a macroscopic system. • In an ecosystem, energy conversions are not completely efficient, and some energy is always lost as heat Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Conservation of Mass • The law of conservation of mass states that matter cannot be created or destroyed • Chemical elements are continually recycled within ecosystems Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings •In a forest ecosystem, most nutrients enter as dust or solutes in rain and are carried away in water •Ecosystems are open systems, absorbing energy and mass and releasing heat and waste products Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Energy, Mass, and Trophic Levels • Autotrophs build molecules themselves using photosynthesis or chemosynthesis as an energy source. • Heterotrophs depend on the biosynthetic output of other organisms • Trophic level – hierarchy describing how organisms obtain their energy Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings (reactants) Energy and nutrients Energy and nutrients pass from pass from primary producers primary producers (autotrophs) (autotrophs) to to primary consumers primary consumers (herbivores) to (herbivores) to secondary secondary consumers (carnivores) to consumers (carnivores) to tertiary tertiary consumers (carnivores consumers that feed on other carnivores) (carnivores that feed on other carnivores) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Detritivores, or decomposers, are consumers that derive their energy from detritus, nonliving organic matter • Prokaryotes and fungi are important detritivores • Decomposition connects all trophic levels Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 55-3 Concept 55.2: Energy and other limiting factors control primary production in ecosystems • Primary production in an ecosystem is the amount of light energy converted to chemical energy by autotrophs during a given time period Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Global Energy Budget • The amount of solar radiation reaching the Earth’s surface limits photosynthetic output of ecosystems • Only a small fraction of solar energy actually strikes photosynthetic organisms, and even less is of a usable wavelength Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 55.3: Energy transfer between trophic levels is typically only 10% efficient • Secondary production of an ecosystem is the amount of chemical energy in food converted to new biomass during a given period of time Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Production Efficiency • When a caterpillar feeds on a leaf, only about one-sixth of the leaf’s energy is used for secondary production • An organism’s production efficiency is the fraction of energy stored in food that is not used for respiration Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 55-9 *one-sixth of the leaf’s energy is used for secondary production *Energy transfer between trophic levels is typically only 10% efficient 100 J Feces Plant material eaten by caterpillar 200 J 67 J 33 J Growth (new biomass) Cellular respiration Trophic Efficiency and Ecological Pyramids • Trophic efficiency is the percentage of production transferred from one trophic level to the next • It usually ranges from 5% to 20% • Trophic efficiency is multiplied over the length of a food chain Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Approximately 0.1% of chemical energy fixed by photosynthesis reaches a tertiary consumer • A pyramid of net production represents the loss of energy with each transfer in a food chain Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 55-10 Tertiary consumers Secondary consumers 100 J 1000 J Primary consumers 10,000 J Primary producers 100,000J 1,000,000 J of sunlight • Each tier represents the dry weight of all organisms in one trophic level • Shows sharp decrease at successively higher trophic levels Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 55.4: Biological and geochemical processes cycle nutrients between organic and inorganic parts of an ecosystem • Life depends on recycling chemical elements • Nutrient circuits in ecosystems involve biotic and abiotic components and are often called biogeochemical cycles Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Biogeochemical Cycles • Gaseous carbon, oxygen, sulfur, and nitrogen occur in the atmosphere and cycle globally • Less mobile elements such as phosphorus, potassium, and calcium cycle on a more local level Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 55-14a Transport over land Solar energy Net movement of water vapor by wind Precipitation Evaporation over ocean from ocean Precipitation over land Evapotranspiration from land Percolation through soil Runoff and groundwater The Carbon Cycle • Carbon-based organic molecules are essential to all organisms • Carbon reservoirs include fossil fuels, soils and sediments, solutes in oceans, plant and animal biomass, and the atmosphere • CO2 is taken up and released through photosynthesis and respiration; additionally, volcanoes and the burning of fossil fuels contribute CO2 to the atmosphere Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 55-14c N2 in atmosphere Assimilation NO3– Nitrogen-fixing bacteria Decomposers Ammonification NH3 Nitrogen-fixing soil bacteria Nitrification NH4+ NO2– Nitrifying bacteria Denitrifying bacteria Nitrifying bacteria The Terrestrial Nitrogen Cycle • The pathway in which nitrogen moves through the ecosystem • Nitrogen is a component of amino acids, proteins, nucleic acids (DNA), ATP • The main reservoir of nitrogen (N2) is the atmosphere, 78% . N2 gas must be converted to other forms. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 4 processes of the Nitrogen Cycle Nitrogen Fixation - process converts N2 into NH4+ (ammonium ions). Done by nitrogen fixing bacteria found in soil or nodules on roots of legumes Examples of legumes: peas, beans, alfalfa, peanuts, clover • NH4+ by ammonification, and NH4+ is decomposed to NO2- and often to NO3– by nitrification • Nitrifying bacteria convert NH4+ in soils • Plants absorb nitrates through roots Bashan, Y. and Levanony, H. (1987) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Ammonification • Breakdown of nitrogen compounds back into ammonia products Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Denitrification • Conversion of NH4+, NO2-, NO3- back to N2 gas (bacteria do this). Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Energy Flow and Geochemical Cycling in an Ecosystem Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 55-17 Fig. 55-18 Winter Summer Fig. 55-16 (a) Concrete dam and weir Nitrate concentration in runoff (mg/L) (b) Clear-cut watershed 80 60 40 20 4 3 2 1 0 Deforested Completion of tree cutting 1965 Control 1966 (c) Nitrogen in runoff from watersheds 1967 1968 Fig. 55-14b CO2 in atmosphere Photosynthesis Photosynthesis Cellular respiration Burning of fossil fuels Phytoand wood plankton Higher-level consumers Primary consumers Carbon compounds in water Detritus Decomposition Toxins in the Environment • Humans release many toxic chemicals, including synthetics previously unknown to nature • In some cases, harmful substances persist for long periods in an ecosystem • One reason toxins are harmful is that they become more concentrated in successive trophic levels • Biological magnification concentrates toxins at higher trophic levels, where biomass is lower Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • PCBs and many pesticides such as DDT are subject to biological magnification in ecosystems • In the 1960s Rachel Carson brought attention to the biomagnification of DDT in birds in her book Silent Spring Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 55-20 Herring gull eggs 124 ppm Lake trout 4.83 ppm Smelt 1.04 ppm Zooplankton 0.123 ppm Phytoplankton 0.025 ppm Depletion of Atmospheric Ozone • Life on Earth is protected from damaging effects of UV radiation by a protective layer of ozone molecules in the atmosphere • Satellite studies suggest that the ozone layer has been gradually thinning since 1975 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 55-23 Ozone layer thickness (Dobsons) 350 300 250 200 100 0 1955 ’60 ’65 ’70 ’75 ’80 ’85 Year ’90 ’95 2000 ’05 • Destruction of atmospheric ozone probably results from chlorine-releasing pollutants such as CFCs produced by human activity Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 55-24 Chlorine atom O2 Chlorine O3 ClO O2 ClO Cl2O2 Sunlight • Scientists first described an “ozone hole” over Antarctica in 1985; it has increased in size as ozone depletion has increased Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 55-25 (a) September 1979 (b) September 2006