Ecosystems

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					Ecosystems

  Chapter 48
                 Ecosystems
   Open systems through which energy flows and
    materials are recycled
   Require energy and nutrient input and generate
    energy and nutrient output
              Modes of Nutrition
   Autotrophs
       Capture sunlight or chemical energy
       Producers
   Heterotrophs
       Extract energy from other organisms or organic
        wastes
       Consumers, decomposers, detritivores
 Simple
Ecosystem   energy
            input from
            sun
  Model
                     PHOTOAUTOTROPHS
                   (plants, other producers)



                           nutrient
                           cycling




                       HETEROTROPHS
                   (consumers, decomposers)



            energy output (mainly heat)
                     Consumers
   Herbivores
   Carnivores                                     fruits             SPRING
                                                            insects
                                    rodents,
   Parasites                       rabbits
                                                             birds

   Omnivores
                                               fruits                 SUMMER
   Decomposers                  rodents,
                                 rabbits                    insects

       Fungi, bacteria                        birds


   Detritivores              Seasonal variation in the diet of an
                              omnivore (red fox)
       Small invertebrates
                Trophic Levels
               Who Eats Whom?
   All the organisms at a trophic level are the
    same number of steps away from the energy
    input into the system

   Producers are closest to the energy input and
    are the first trophic level
Trophic Levels in Prairie
        Fourth-level consumers (heterotrophs):
   5th Top carnivores, parasites,
       detritivores, decomposers

        Third-level consumers (heterotrophs):
  4th   Carnivores, parasites, detritivores,
        decomposers
        Second-level consumers (heterotrophs):
  3rd Carnivores, parasites, detritivores,
      decomposers
        First-level consumers (heterotrophs):
  2nd
        Herbivores, parasites, detritivores,
        decomposers
        Primary producers (autotrophs):
   1st Photoautotrophs, chemoautotrophs
     Food Chain                  marsh hawk



   A straight-line sequence
                               upland sandpiper

    of who eats whom

   Simple food chains are       garter snake

    rare in nature
                                  cutworm



                                    plants
Tall-Grass Prairie Food Web
           marsh hawk




     sandpiper          crow




   snake


   frog
                                          weasel   badger   coyote
             spider

                               sparrow

                                         vole      pocket     ground
  earthworms, insects                              gopher     squirrel



                               grasses, composites
               Energy Losses

   Energy transfers are never 100 percent efficient

   Some energy is lost at each step
       How?

       Heat

   Limits the number of trophic levels in an ecosystem
                                Grazing      Detrital
                                Food Web     Food Web

                                   Webs
                 Two Types of Food Energy Input:
                 Energy Input:

    Transfers:                                Transfers:
              Producers                                     Producers
          (photosynthesizers)                           (photosynthesizers)



                                                                                  energy
energy                           energy       energy                              losses
in             herbivores        losses       in            decomposers
                                                            decomposers           as
organic                          as           organic                             metabolic
                                 metabolic                                        heat
wastes,                                       wastes,
                                 heat                                             & as net
remains        carnivores        & as net
                                              remains        detritivores
                                                              detritivores        export
                                 export                                           from
                                 from                                             ecosystem
                                 ecosystem
              decomposers




     Energy                                       Energy                 Figure 48.7
     Output                                       Output
                                                                             Page 871
Biological Magnification
A nondegradable or slowly degradable
substance becomes more and more
concentrated in the tissues of organisms at
higher trophic levels of a food web
           DDT in Food Webs
   Effective chemical for killing mosquitoes
   Accumulates in fatty tissues
   Synthetic pesticide banned in United States
    since the 1970s
   Still persist in sediments



   Birds that are carnivores accumulate DDT in
    their tissues, produce brittle egg shells
DDT in an Estuary (1967)
 DDT Residues (ppm wet weight of whole live organism)

 Ring-billed gull fledgling (Larus delawarensis)   75.5
 Herring gull (Larus argentatus)                   18.5
 Osprey (Pandion haliaetus)                        13.8
 Green heron (Butorides virescens)                 3.57
 Atlantic needlefish (Strongylira marina)          2.07
 Summer flounder (Paralychthys dentatus)           1.28
 Sheepshead minnow (Cyprinodon variegatus)         0.94
 Hard clam (Mercenaria mercenaria)                 0.42
 Marsh grass shoots (Spartina patens)              0.33
 Flying insects (mostly flies)                     0.30
 Mud snail (Nassarius obsoletus)                   0.26
 Shrimps (composite of several samples)            0.16
 Green alga (Cladophora gracilis)                  0.083
 Plankton (mostly zooplankton)                     0.040
 Water                                             0.00005
                 Primary Productivity
   Gross primary productivity is ecosystem’s total rate of
    photosynthesis for the ecosystem during an interval

   Net primary productivity is rate at which producers store energy
    in tissues in excess of their aerobic respiration
       NPP accounts for the organic mass of plants (growth) and represents storage of
        chemical energy available to consumers.

   NPP = GPP - Respiration
Primary Productivity Varies

   Seasonal variation

   Variation by habitat

   The harsher the environment, the
    slower plant growth, the lower the
    primary productivity
              Ecological Pyramids
   Biomass Pyramid
   has tiers symbolizing the total dry weight of all
    organisms in an ecosystem's levels at any given
    time.
    Biomass represents chemical energy stored in the
    organic matter of a trophic level.
   Most narrow sharply from producers at the base to
    top-level carnivores at the top.
          Silver Springs Study
   Aquatic ecosystem in Florida
   Site of a long-term study of a grazing food web

                        g/m2
                                      third-level carnivores
                        1.5           (gar, large-mouth bass)


                        1.1           second-level consumers
decomposers,
                                      (fishes, invertebrates)
detritivores
(bacteria,                            first-level consumers
crayfish)               37            (herbivorous fishes,
                                      turtles, invertebrates)

                               809    primary producers (algae,
    5                                 eelgrass, rooted plants)
                 Energy Pyramid
   Reflects trophic structure most accurately because it
    is based on energy looses at each level
          Pyramid of Energy Flow
     Primary producers trapped about 1.2 percent of
      the solar energy that entered the ecosystem
     6-16% passed on to next level (10%)



top carnivores            21       decomposers + detritivores = 5,080
carnivores
                    383
herbivores
                    3,368
producers          20,810 kilocalories/square meter/year

                                                           Figure 48.11
                                                            Page 874
      ENERGY INPUT:
                          Energy Flow In
                1,700,000 kilocalories
                                       Incoming solar
                                       energy not
                            Silver Springs
                                       harnessed:
                                       1,679,190 (98.8%)
                      20,810               Energy losses as
                      (1.2%)               metabolic heat &
Energy in
                         Producers         as net export
organic
                                           from
wastes and          To next trophic level:
                                           ecosystem:
remains:
                                 3,368
          4,245                              13,197
                          Herbivores
                                383
            720                               2,265
                          Carnivores
                                 21             272
          90            Top carnivores

            5           Decomposers,      16
                         detritivores 5,060
Figure 48.12               ENERGY OUTPUT: 20,810              1,679,190
 Page 874            Total annual energy flow:    1,700,000 (100%)
            All Heat in the End
   At each trophic level, the bulk of the energy
    received from the previous level is used in
    metabolism
   This energy is released as heat energy and lost
    to the ecosystem
   Eventually all energy is released as heat
      Biogeochemical Cycle
   Influence the availability of essential elements
    in ecosystems

   The amount of nutrients cycling is greater
    than those entering or leaving

   Main reservoir for the nutrient is in the
    environment
 Environmental Inputs Environmental Outputs
       of Nutrients         of Nutrients
 Precipitation        Runoff

 Metabolism           Evaporation

 Weathering
    Three Categories
   Hydrologic cycle
       Water

   Atmospheric cycles
       Nitrogen and carbon

   Sedimentary cycles
       Phosphorus and sulfur
                   Hydrologic Cycle
                            Atmosphere

                        wind-driven water vapor             precipitation
                                 40,000                      onto land
                                                              111,000
evaporation precipitation        evaporation from land
from ocean into ocean         plants (evapotranspiration)
  425,000     385,000                   71,000
                                                                     surface and
                                                                     groundwater
                                                                     flow 40,000



        Ocean                                                           Land

                                                                      Figure 48.14
                                                                      Page 876
     Hubbard Brook Experiment
   A watershed was experimentally stripped of
    vegetation
   All surface water draining from watershed was
    measured
   Removal of vegetation caused a six-fold
    increase in the calcium content of the runoff
    water
Hubbard Brook Experiment

                  losses from
                  disturbed watershed




     time of
  deforestation
                            losses from
                            undisturbed watershed




                                              Figure 48.15
                                                Page 877
            Carbon Cycle

   Carbon moves through the atmosphere
    and food webs on its way to and from
    the ocean, sediments, and rocks

   Sediments and rocks are the main
    reservoir
 diffusion between
 atmosphere and ocean




       bicarbonate and               combustion of fossil fuels
         carbonate in
         ocean water


   photosynthesis     aerobic
                    respiration

         marine food
           webs

                  death,
incorporation sedimentation
into sediments                    uplifting
                                                    sedimentation
         marine sediments



       Carbon Cycle - Marine                                        Figure 48.16
                                                                    Page 878
                                 atmosphere


        volcanic action                              combustion of
                                                      fossil fuels

                      photosynthesis     aerobic combustion
        terrestrial                    respiration of wood
          rocks


                                           sedimentation
       weathering           land food
                              webs

        soil water
                                                      peat,
                            death, burial,            fossil
leaching,                   compaction over           fuels
  runoff                    geologic time




Carbon Cycle - Land                                        Figure 48.16
                                                           Page 878
          Carbon in the Oceans
   Most carbon in the ocean is dissolved
    carbonate and bicarbonate
   Ocean currents carry dissolved carbon
          Carbon in Atmosphere
   Atmospheric carbon is mainly carbon
    dioxide
   Carbon dioxide is added to atmosphere
       Aerobic respiration, volcanic action, burning
        fossil fuels
   Removed by photosynthesis
        Greenhouse Effect

   Greenhouse gases impede the escape
    of heat from Earth’s surface




                                   Figure 48.18, Page 880
       Global Warming

Long-term increase in the temperature of
        Earth’s lower atmosphere




                                Figure 48.19, Page 881
        Carbon Dioxide Increase

   Carbon dioxide levels fluctuate seasonally

   The average level is steadily increasing

   Burning of fossil fuels and deforestation are
    contributing to the increase
        Other Greenhouse Gases
   CFCs - synthetic gases used in plastics and in
    refrigeration
   Methane - produced by termites and bacteria
   Nitrous oxide - released by bacteria, fertilizers,
    and animal wastes
            Nitrogen Cycle

   Nitrogen is used in amino acids and nucleic
    acids

   Main reservoir is nitrogen gas in the
    atmosphere
                          Nitrogen Cycle
                               gaseous nitrogen (N2)
                                  in atmosphere
     nitrogen fixation
        by industry
                             food webs
                               on land
                 uptake by excretion, death, uptake by
    fertilizers autotrophs decomposition autotrophs

                           nitrogenous         NO3-
nitrogen                  wastes, remains     in soil      dentrification
fixation

  NH3-,NH4+              ammonification 2. Nitrification
   in soil

leaching                   1. Nitrification     NO2-           leaching
                                               in soil                      Figure 48.21
                                                                             Page 882
          Nitrogen Fixation
   Plants cannot use nitrogen gas
   Nitrogen-fixing bacteria convert
    nitrogen gas into ammonia (NH3)
   Ammonia and ammonium can be taken
    up by plants
Ammonification & Nitrification

   Bacteria and fungi carry out ammonification
       conversion of nitrogenous wastes to ammonia

   Nitrifying bacteria convert ammonium to
    nitrites and nitrates
                 Nitrogen Loss
   Nitrogen is often a limiting factor in
    ecosystems
   Nitrogen is lost from soils via leaching and
    runoff
   Denitrifying bacteria convert nitrates and
    nitrites to nitrogen gas
               Human Effects
   Humans increase rate of nitrogen loss by
    clearing forests and grasslands
   Humans increase nitrogen in water and air by
    using fertilizers and by burning fossil fuels
   Too much or too little nitrogen can
    compromise plant health
         Phosphorus Cycle

   Phosphorus is part of phospholipids and
    all nucleotides
   It is the most prevalent limiting factor in
    ecosystems
   Main reservoir is Earth’s crust; no
    gaseous phase
                   Phosphorus Cycle


                                                mining          FERTILIZER
  excretion                GUANO
                                                                                          agriculture
                uptake     weathering                                         uptake
                  by                                                            by
              autotrophs                                                    autotrophs
                                            weathering
  MARINE             DISSOLVED                                  DISSOLVED IN             LAND
   FOOD               IN OCEAN                                   SOILWATER,              FOOD
   WEBS                 WATER                                  LAKES, RIVERS             WEBS
              death,                                                      death,
          decomposition                                               decomposition
                            settling
sedimentation                 out                        leaching, runoff

                                            uplifting
        MARINE SEDIMENTS                                         TERRESTRIAL ROCKS
                                        over geologic time




                                                                                 Figure 48.23, Page 884
              Human Effects
   In tropical countries, clearing lands for
    agriculture may deplete phosphorus-poor
    soils
   In developed countries, phosphorus runoff is
    causing eutrophication of waterways

				
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