Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings “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

(reactants)

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Energy and nutrients pass from primary producers (autotrophs) to primary consumers (herbivores) to secondary consumers (carnivores) to tertiary consumers (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

Fig. 55-3

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 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

Fig Cellular respiration 100 J Growth (new biomass) Feces 200 J 33 J 67 J Plant material eaten by caterpillar *one-sixth of the leaf’s energy is used for secondary production *Energy transfer between trophic levels is typically only 10% efficient

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 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

Fig Primary producers 1000 J 1,000,000 J of sunlight 100 J 10,000 J 100,000J Primary consumers Secondary consumers Tertiary consumers

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 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

Fig a Precipitation over land Transport over land Solar energy Net movement of water vapor by wind Evaporation from ocean Percolation through soil Evapotranspiration from land Runoff and groundwater Precipitation over ocean

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 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 CO 2 is taken up and released through photosynthesis and respiration; additionally, volcanoes and the burning of fossil fuels contribute CO 2 to the atmosphere

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig c Decomposers N 2 in atmosphere Nitrification Nitrifying bacteria Nitrifying bacteria Denitrifying bacteria Assimilation NH 3 NH 4 NO 2 NO 3 + – – Ammonification Nitrogen-fixing soil bacteria Nitrogen-fixing bacteria

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 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 (N 2 ) is the atmosphere, 78%. N 2 gas must be converted to other forms. The Terrestrial Nitrogen Cycle

4 processes of the Nitrogen Cycle Nitrogen Fixation - process converts N 2 into NH 4 + (ammonium ions). Done by nitrogen fixing bacteria found in soil or nodules on roots of legumes Examples of legumes: peas, beans, alfalfa, peanuts, clover

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings NH 4 + by ammonification, and NH 4 + is decomposed to NO 2 - and often to NO 3 – by nitrification Nitrifying bacteria convert NH 4 + 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 NH 4 +, NO 2 -, NO 3 - back to N 2 gas (bacteria do this).

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Energy Flow and Geochemical Cycling in an Ecosystem

Fig

Fig WinterSummer

Fig (c) Nitrogen in runoff from watersheds Nitrate concentration in runoff (mg/L) (a) Concrete dam and weir (b) Clear-cut watershed Control Completion of tree cutting Deforested

Fig b Higher-level consumers Primary consumers Detritus Burning of fossil fuels and wood Phyto- plankton Cellular respiration Photo- synthesis Photosynthesis Carbon compounds in water Decomposition CO 2 in atmosphere

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 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

Fig Lake trout 4.83 ppm Concentration of PCBs Herring gull eggs 124 ppm Smelt 1.04 ppm Phytoplankton ppm Zooplankton ppm

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 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

Ozone layer thickness (Dobsons) Fig Year ’ ’95’90’85 ’80 ’75’70 ’65 ’

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Destruction of atmospheric ozone probably results from chlorine-releasing pollutants such as CFCs produced by human activity

Fig O2O2 Sunlight Cl 2 O 2 Chlorine Chlorine atom O3O3 O2O2 ClO

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Scientists first described an “ozone hole” over Antarctica in 1985; it has increased in size as ozone depletion has increased

Fig (a) September 1979(b) September 2006