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Ecosystems:
What Are They
and How Do They
Work?
Chapter 3
Learning Objectives

        What is ecology?
        What basic processes keep us and other
         organisms alive?
        What are the major components of an
         ecosystem?
        What happens to energy in an ecosystem?
        What are soils and how are they formed?
        What happens to matter in an ecosystem?
        How do scientists study ecosystems?
What is Ecology?

       Ecology is …
           the study of how organisms interact
            with each other and with their
            nonliving environment.
           The study of connections in nature
Categories of Life
Organisms and Species

    Organisms – Any form of life
    Species – Groups of organisms that resemble one
     another in appearance, behavior, chemistry, and
     genetic makeup
    There are 4 million to 100 million species on Earth.
        Most known species are microorganisms that are
         too small to be seen with the naked eye.
        10 million to 15 million other species
        1.4 million species have been named (most are
         insects)
Other animals
Known species                    281,000
1,412,000




Insects
751,000                                    Fungi
                                           69,000

                                     Prokaryotes
                                     4,800



                           Plants
                           248,400

                Protists
                57,700                Fig. 3-3, p. 52
Populations, Communities, &
Ecosystems

       Members of a species interact in groups
        called populations.
       Populations of different species living
        and interacting in an area form a
        community.
       A community interacting with its
        physical environment of matter and
        energy is an ecosystem.
Universe
      Galaxies
    Solar systems          Biosphere
       Planets

        Earth

      Biosphere

     Ecosystems            Ecosystems
    Communities

     Populations
     Organisms                              Realm of ecology
                           Communities
   Organ systems

       Organs

       Tissues

        Cells

     Protoplasm
                                  Populations

      Molecules

       Atoms          Organisms
Subatomic Particles
                                                         Fig. 3-2, p. 51
The Four Spheres
The Four Spheres

       Earth is our life support system.
       Earth is made up of interconnected
        spherical layers that contain air, water,
        soil, minerals, and life.
           Atmosphere (air)
           Hydrosphere (water)
           Geosphere (rock)
           Biosphere (living things)
The Atmosphere

       A thin envelope of air around the planet.
       The atmosphere is divided into four
        layers based on temperature changes
        that occur at different distances above
        the Earth’s surface.
           Troposphere
           Stratosphere
           Mesosphere
           Thermosphere
The Hydrosphere

       Consists of earth’s water
       Water can be found as liquid water, ice,
        and water vapor.
           Liquid water: surface and
            underground
           Ice: polar ice, icebergs, permafrost
           Water Vapor: gas in the atmosphere
The Geosphere
   The Earth can also be divided into layers based on physical
    properties or chemical properties.
   3 Layers (Chemical Properties):
       Crust
       Mantle
       Core
   5 Layers (Physical Properties):
       Lithosphere
       Asthenosphere
       Mesosphere
       Outer Core
       Inner Core
The Biosphere

       All of Earth’s living things.
       All of Earth’s ecosystems together.
Everything is linked to
everything else.
What Sustains
Life on Earth?
3 Interconnected Forces

        Solar Energy
        The Cycling of Matter
        Gravity
Biosphere




Carbon   Phosphorus   Nitrogen      Water   Oxygen
 cycle      cycle      cycle        cycle    cycle


               Heat in the environment



 Heat                  Heat                 Heat
                                                     Fig. 3-7, p. 55
Solar Energy

       The flow of high-quality energy from the
        sun through materials and living things
        in their feeding interactions, into the
        environment as low-quality energy, and
        eventually back into space as heat.
       Solar energy flows through the
        biosphere, warms the atmosphere,
        evaporates and recycles water,
        generates winds, and supports plant
        growth.
Solar Energy

       About one-billionth of the sun’s output
        of energy reaches the earth.
       Much of the energy is reflected away or
        absorbed by the chemicals, dust, and
        clouds in the atmosphere.
Solar
    radiation
                                     Energy in = Energy out


                              Reflected by
                              atmosphere (34% )       Radiated by
UV radiation                                          atmosphere
                                                      as heat (66%)
                           Lower Stratosphere
    Absorbed                 (ozone layer)
    by ozone    Visible     Troposphere Greenhouse
                Light                        effect
                                        Heat
                Absorbed
                by the                            Heat radiated
                earth                             by the earth




                                                                  Fig. 3-8, p. 55
Ecosystem Components
Biomes and Aquatic Life Zones

       Life exists on land systems called
        biomes and in freshwater and ocean
        aquatic life zones.
           Biome = The terrestrial portion of the
            biosphere.
           Aquatic Life Zones = Water parts of
            the biosphere
Biotic and Abiotic Factors

        Ecosystems consist of nonliving and
         living components.
        Biotic = living components
            Producers
            Consumers
            Decomposers
        Abiotic = nonliving components
Oxygen     Sun
                                                 (O2)

                        Producer
                                                  Carbon dioxide (CO2)
                                                     Secondary consumer
                                            Primary
                                                            (fox)
                                           consumer
                                            (rabbit)
Precipitation                  Producers
             Falling leaves
               and twigs
                                                   Soil decomposers


             Water



                                                                  Fig. 3-10, p. 57
Factors that Limit Population Growth
   Different species and their populations thrive under different physical
    and chemical conditions.
   Availability of matter and energy can limit the number of organisms in a
    population.
   Limiting Factor Principle = Too much or too little of any abiotic factor can
    limit or prevent growth of a population, even if all other factors are at or
    near the optimum range of tolerance.
       Precipitation/Amount of Water
       Soil nutrients
       Temperature
       Sunlight
       Salinity

       Dissolved Oxygen Content
Producers (Autotrophs)

        Some organisms in ecosystems can
         produce the food they need from
         chemicals in their environment.
        Photosynthesis
        Chemosynthesis
Consumers (Heterotrophs)

       Consumers get their food by eating or
        breaking down all or parts of other
        organisms or their remains.
           Herbivores/Primary Consumers – eat
            producers
           Carnivores/Secondary Consumers – eat
            herbivores
           Tertiary Consumers – eat other
            carnivores
           Omnivores – eat both plants and
            animals
Decomposers and Detritrivores

       Decomposers
           Specialized organisms that recycle
            nutrients in ecosystems.
           Digest or degrade living or dead organisms
            into simpler inorganic compounds that
            producers can take up form soil and water
            to use as nutrients.
       Detritrivores
           Insects and other scavengers that feed on
            the wastes or dead bodies of other
            organisms.
Scavengers                       Decomposers




                                Termite
         Bark beetle Carpenter    and
         engraving      ant    carpenter
Long-
horned               galleries ant work Dry rot
                                         fungus
beetle
holes                                                Wood
                                                     reduced
                                                     to      Mushroom
                                                     powder


Time                                 Powder broken down by decomposers
progression                               into plant nutrients in soil

                                                             Fig. 3-13, p. 61
Energy Flow
     in
Ecosystems
Food Chains and Food Webs

       Food chains and webs show how eaters, the
        eaten, and the decomposed are connected to
        one another in an ecosystem.
       All organisms, whether dead or alive, are
        potential sources of food for other organisms.

       There is little matter wasted in natural
        ecosystems.
       Trophic Levels = Feeding Levels
First Trophic      Second Trophic          Third Trophic          Fourth Trophic
                    Level              Level                   Level                  Level
                Producers            Primary                Secondary              Tertiary
                 (plants)           consumers               consumers            consumers
                                   (herbivores)            (carnivores)       (top carnivores)

                                Heat                Heat                   Heat



 Solar
energy


                                                    Heat Heat

         Heat                                                                                      Heat




                                    Detritivores           Heat
                          (decomposers and detritus feeders)



                                                                                           Fig. 3-17, p. 64
Blue whale                 Humans             Sperm whale



    Crabeater                                        Elephant
    seal                                             seal
                              Killer whale

             Leopard
             seal
Adelie
penguins                            Emperor
                                    penguin




                                                       Squid
                Petrel                 Fish

                 Carnivorous plankton




     Krill                                      Herbivorous
                                                plankton
                       Phytoplankton
                                                                Fig. 3-18, p. 65
Losing Energy in Food Chains and
Webs

       There is a decrease in the amount of
        energy available to each succeeding
        organisms in a food chain or web. (2nd
        Law of Thermodynamics)
       Each trophic level contains a certain
        amount of biomass.
       Only a small portion of what is eaten and
        digested is actually converted into an
        organism’s biomass.
       The amount available to each
        successive trophic level declines.
Ecological Efficiency

        The percentage of usable energy transferred as
         biomass from one trophic level to the next.
        It ranges from 2% to 40% or a loss of 60% to
         98%.
        10% ecological efficiency is typical
Heat



                       Tertiary   Heat
                     consumers        Decomposers
                      (human)

                                    Heat
     10
                    Secondary
                    consumers
                      (perch)
                                       Heat
     100

               Primary
    1,000     consumers
            (zooplankton)                     Heat

     10,000       Producers
 Usable energy (phytoplankton)
  Available at
Each tropic level
(in kilocalories)
                                                       Fig. 3-19, p. 66
Ecological Efficiency

        Energy flow pyramids explain why the Earth can
         support more people if they eat at lower trophic
         levels by consuming grains, vegetables, and
         fruits.
        Food chains and webs rarely have more than
         four or five trophic levels.
Biodiversity
Biodiversity

        A vital renewable resource is the biodiversity
         found in the earth’s variety of genes, species,
         ecosystems, and ecosystem processes.
        4 Components
            Functional Diversity

            Ecological Diversity

            Species Diversity

            Genetic Diversity
Functional Diversity

  The biological and chemical
   processes such as energy
    flow and matter recycling
   needed for the survival of
   species, communities and
          ecosystems.
Ecological Diversity


      The variety of terrestrial
            and aquatic
       ecosystems found in an
        area or on the earth.
Species Diversity


      The number of species
        present in different
             habitats.
Genetic Diversity


       The variety of genetic
          material within a
       species or population.
Biodiversity Loss and Species
Extinction

        Human activities are destroying and degrading
         the habitats for many wild species and driving
         some of them to premature extinction.
        Sooner or later all species become extinct
         because they cannot respond successfully to
         changing environmental conditions.

        Current extinction rates are 100 to 10,000 times
         higher than natural extinction rates because of
         human activities.
Biodiversity Loss and Species
Extinction

     H = Habitat destruction and degradation
     I = Invasive species
     P = Pollution
     P = human Population growth
     O = Overexploitation (overhunting, over consumption)
Why Should We Care About
Biodiversity?

       Biodiversity provides us with:
           Natural Resources (food water, wood, energy, and
            medicines)

           Natural Services (air and water purification, soil
            fertility, waste disposal, pest control)

           Aesthetic pleasure
In-Class Assignment

    1.   Read the Core Case Study on page 50.
    2.   Summarize the importance of insects in the
         earth’s biodiversity.
    3.   Share with the class.
Solutions

    Goals, strategies and tactics for
     protecting biodiversity.




                             Figure 3-16
Soil: A Renewable Resource
What is Soil? Why is it Important?

        Soil is a slowly renewed resource that provides
         most of the nutrients needed for plant growth
         and also helps purify water.
        Soil is a thin covering over most land that is a
         complex mixture of eroded rock, mineral
         nutrients, decaying organic matter, water, air,
         and living organisms.

        Soil forms when rock is broken down into
         fragments and particles by physical, chemical,
         and biological weathering.
What is Soil? Why is it Important?

        Over hundreds to thousands of years various
         types of life build up layers of inorganic and
         organic matter on soil’s original bedrock.
        Formation of 1 cm of soil can take from 15
         years to hundreds of years.
        Soil is the base of life on land.
        Producers get the nutrients they need from soil
         and water.
        You are mostly composed of soil nutrients
         imported into your body by the food you eat.
What is Soil? Why is it Important?

        Soil helps cleanse water that flows through it.
        Soil helps decompose and recycle
         biodegradable wastes.
        Soil helps remove carbon dioxide from the
         atmosphere and stores it as carbon
         compounds.
Mature Soils

        Soils that have developed over a long time.
        Arranged in soil horizons, each has a distinct
         texture and composition.
        Soil Profile – a cross-sectional view of the
         horizons in a soil.
        Most mature soils have at least three of the
         possible horizons.
Wood
              Oak tree   sorrel
                            Lords and   Dog violet                 Organic debris
                            ladies                Grasses and      builds up        Rock
                                                  small shrubs                   fragments
                            Earthworm
                Fern                    Millipede                      Moss and
                                 Honey
                                 fungus                                lichen
O horizon                                         Mole
Leaf litter
A horizon
Topsoil

B horizon                                                                         Bedrock
Subsoil                                                                       Immature soil
                                                                       Regolith
C horizon                                                         Young soil
                                                        Pseudoscorpion
Parent                                                      Mite
material                                                      Nematode

          Root system
                                                              Actinomycetes
                                        Red Earth
                                        Mite                Fungus
                         Mature soil                  Bacteria
                                         Springtail                            Fig. 3-23, p. 68
Soil Layers

        O Horizon – Surface Litter Layer
            Freshly fallen or partially decomposed leaves

            Twigs

            Crop wastes

            Animal Wastes

            Normally brown or black
Soil Layers

        A Horizon – Topsoil
            Porous mixture of partially decomposed bodies of
             dead plants and animals (Humus)

            Inorganic materials such as clay, silt, sand

            Fertile soil that produces high crop yields has a
             thick topsoil layer with lots of humus.

                Helps topsoil hold water and nutrients taken up
                 by plant roots.
Soil Layers

   2 Upper Layers
       Most plant roots and organic matter are located here

       As long as vegetation anchors these layers, the soil will hold
        water and release it as needed

       Full of bacteria, fungi, earthworms, and small insects

       The color of topsoil is a clue to its ability to grow crops.

           Dark brown or black = rich in nitrogen and organic matter

           Gray, yellow, red = low in nitrogen and organic matter.
Soil Layers

    B Horizon – Subsoil and C Horizon – Parent material
        Contain most inorganic matter

            Broken down rock

            Transported by water from the A horizon
Wood
              Oak tree   sorrel
                            Lords and   Dog violet                 Organic debris
                            ladies                Grasses and      builds up        Rock
                                                  small shrubs                   fragments
                            Earthworm
                Fern                    Millipede                      Moss and
                                 Honey
                                 fungus                                lichen
O horizon                                         Mole
Leaf litter
A horizon
Topsoil

B horizon                                                                         Bedrock
Subsoil                                                                       Immature soil
                                                                       Regolith
C horizon                                                         Young soil
                                                        Pseudoscorpion
Parent                                                      Mite
material                                                      Nematode

          Root system
                                                              Actinomycetes
                                        Red Earth
                                        Mite                Fungus
                         Mature soil                  Bacteria
                                         Springtail                            Fig. 3-23, p. 68
Soil

          The spaces (pores) between the solid organic
           and inorganic particles contain air and water.
          Plants need the oxygen for cellular respiration.
          Precipitation that reaches the soil percolates
           through the soil layers and occupies many of
           the soil’s open spaces or pores. (Infiltration)
          As the water seeps down it dissolves various
           minerals and organic matter in the upper layers
           and carries them to lower layers. (leaching)
Soil Properties

        Soils vary in the size of the particles they
         contain, the amount of space between these
         particles, and how rapidly water flows through
         them.
        Clay – Very small particles
        Silt – Medium particles
        Sand – Largest particles
        Soil Texture – The relative amounts of the
         different sizes and types of these mineral
         particles.
Sand                   Silt                 Clay
0.05–2 mm           0.002–0.05 mm      less than 0.002 mm
 diameter              diameter              Diameter




            Water                          Water




   High permeability                Low permeability
                                                       Fig. 3-25, p. 70
Mosaic of
                     closely
                     packed
                     pebbles,
                     boulders
                     Weak humus-
                     mineral mixture                    Alkaline,
                                                        dark,
                     Dry, brown to
                                                        and rich
                     reddish-brown
                                                        in humus
                     with variable
                     accumulations                      Clay,
                     of clay, calcium                   calcium
                     and carbonate,                     compounds
                     and soluble
   Desert Soil                           Grassland Soil
                     salts
(hot, dry climate)                      semiarid climate)
                                                            Fig. 3-24a, p. 69
Acidic
                            light-colored
                            humus

                            Iron and
                            aluminum
                            compounds
                            mixed with
                            clay
Tropical Rain Forest Soil
(humid, tropical climate)
                                            Fig. 3-24b, p. 69
Forest litter leaf
                        mold
                        Humus-mineral
                        mixture
                        Light, grayish-
                        brown, silt loam
                        Dark brown
                        firm clay



Deciduous Forest Soil
(humid, mild climate)
                                             Fig. 3-24b, p. 69
Acid litter
                         and humus
                         Light-colored
                         and acidic

                         Humus and
                         iron and
                         aluminum
                         compounds

Coniferous Forest Soil
 (humid, cold climate)
                                         Fig. 3-24b, p. 69
Matter Cycling in
Ecosystems
Nutrient Cycles: Global Recycling
   Global cycles recycle nutrients through the earth’s air, land,
    water, and living organisms and, in the process, connect past,
    present, and future forms of life.
   Nutrients –the elements and compounds that organisms need to
    live, grow, and reproduce
   Biogeochemical Cycles
       Water

       Carbon

       Nitrogen

       Phosphorus

       Sulfur
The Water Cycle
     A vast global cycle collects, purifies,
      distributes, and recycles the Earth’s fixed
      supply of water.
     Also called the hydrologic cycle.
     Powered by energy from the sun and by
      gravity.
     84% of water vapor in the atmosphere
      comes from oceans.
     Most precipitation becomes surface runoff
Water’s Unique Properties
    There are strong forces of attraction between
     molecules of water.
    Water exists as a liquid over a wide
     temperature range.
    Liquid water changes temperature slowly.
    It takes a large amount of energy for water to
     evaporate.
    Liquid water can dissolve a variety of
     compounds.
    Water expands when it freezes.
Rain clouds
                                                  Condensation


                                                Transpiration Evaporation
            Precipitation               Transpiration
               to land                  from plants
Precipitation                                                              Precipitation
                                                          Evaporation
                                         Surface runoff    from land Evaporation
                               Runoff                                 from ocean   Precipitation
                                             (rapid)
                                                                                     to ocean


Infiltration and                                                 Surface
Percolation                                                       runoff
                                                                 (rapid)
                            Groundwater movement (slow)
                                                                      Ocean storage




                                                                                       Fig. 3-26, p. 72
Surface Run Off

       Replenishes streams and lakes
       Causes soil erosion
       Sculpts the landscape
       Transports nutrients
Effects of Human Activities on the
Water Cycle

        We alter the water cycle by…
            Withdrawing large amounts of fresh water
            Clearing vegetation and eroding soils
            Polluting surface and underground water
            Contributing to climate change
The Carbon Cycle
   Carbon cycles through the earth’s air, water,
    soil, and living organisms and depends on
    photosynthesis and respiration.
   Carbon is the basic building block of the
    carbohydrates, fats, proteins, DNA, and other
    organic compounds necessary for life.
   The carbon cycle is based on carbon dioxide
    (CO2)
Fig. 3-27, pp. 72-73
The Carbon Cycle:
Earth’s Thermostat
    If the carbon cycle removes too much CO2
     from the atmosphere, the atmosphere will
     cool.
    If the carbon cycle generates too much CO2
     the atmosphere will get warmer.
    Even slight changes in the cycle can affect
     climate and help determine the types of life
     that can exist on various parts of the Earth.
The Carbon Cycle:
How it Works
   Terrestrial producers remove CO2 from the
    atmosphere.
   Aquatic producers remove CO2 from the water.
   All producers use photosynthesis to convert CO2
    into complex carbohydrates (like glucose)
   The cells in consumers carry out aerobic respiration.
    They break down glucose and convert the glucose
    back to CO2 for reuse by consumers.
   The link between photosynthesis and aerobic
    respiration circulates carbon in the biosphere.
The Carbon Cycle:
How it Works
   Some carbon atoms take a long time to recycle.
   Over millions of years, buried deposits of dead
    plant matter and bacteria are compressed
    between layers of sediment, where they form
    carbon-containing fossil fuels.
   This carbon is not released to the atmosphere
    as CO2 for recycling until these fuels are
    extracted and burned.
   In the past 50 years, we have extracted and
    burned fossil fuels that took millions of years to
    form.
The Carbon Cycle:
The Role of Oceans
    Some of the atmosphere’s carbon dioxide
     dissolves in ocean water and the ocean’s
     photosynthesizing producers remove some.
    As the ocean water warms, some of the
     dissolved CO2 returns to the atmosphere
    Some ocean organisms build their shells and
     skeletons by using dissolved CO2 molecules.
Effects of Human Activities on the
Carbon Cycle
   We alter the carbon cycle by…
       Clear trees and plants that absorb CO2
        through photosynthesis faster than they can
        grow back
       Add large amounts of CO2 by burning fossil
        fuels and wood.
   Increased concentrations of can enhance the
    planet’s natural greenhouse effect.
   Global warming disrupts global food production
    and wildlife habitats, alter temperature and
    precipitation patterns, and raise the average
    sea level in various parts of the world.
CO2 emissions from fossil fuels
                   (billion metric tons of carbon equivalent)




         Year
                                                    Low
                                                           projection
                                                                High




                                              projection




Fig. 3-28, p. 74
The Nitrogen Cycle
   Different types of bacteria help recycle nitrogen through
    the Earth’s air, water, soil and living organisms.
   Nitrogen is…
       The most abundant gas in the atmosphere
       Crucial component of proteins, vitamins, nucleic acids
   N2 cannot be absorbed and used directly as a nutrient by
    multicellular plants or animals.
The Nitrogen Cycle
   Two natural processes fix N2 into useful compounds
       Lightning

       Nitrogen Cycle

           Nitrogen-fixing bacteria in soil and aquatic environments
            convert (fix) gaseous nitrogen (N2 ) into ammonia (NH3)
            which is later converted into ammonium ions (NH4+) that can
            be used by plants.

           Ammonia not taken up by plants undergoes nitrification.
            Specialized soil bacteria convert the NH3 and NH4+ into
            nitrite ions (NO2-) which are toxic to plants, and then to
            nitrate (NO3-) ions which are taken up by the roots of plants.

           Animals get their nitrogen by eating plants or plant-eating
            animals.
The Nitrogen Cycle
   Plants and animals return nitrogen-rich organic compounds
    to the environment as wastes, cast-off particles, and
    through their bodies when they die.
   In ammonificiation, large numbers of specialized
    decomposer bacteria convert organic material into simple
    nitrogen-containing inorganic compounds such as ammonia
    (NH3) and water-soluble salts containing ammonium ions
    (NH4+).
   In denitrification, nitrogen leaves the soil as specialized
    bacteria in waterlogged soil and in the bottom sediments of
    lakes, oceans, swamps, and bogs to convert NH3 and NH4+
    back into nitrite and nitrate ions, then into nitrogen gas (N2)
    and nitrous oxide gas (N2O). These gases are released to
    the atmosphere to begin the nitrogen cycle again.
Gaseous nitrogen (N2)
                                            in atmosphere




                                           Food webs on land
Nitrogen fixation




       Fertilizers




                                                                    Uptake by        Loss by
                     Uptake by autotrophs Excretion, death,         autotrophs denitrification
                                           decomposition

  Ammonia, ammonium in soil             Nitrogen-rich wastes,    Nitrate in soil
                                            remains in soil

                                                                     Nitrification
                                            Ammonification                             Loss by
 Loss by                                                                               leaching
 leaching                                                        Nitrite in soil
                                      Nitrification                                Fig. 3-29, p. 75
Effects of Human Activities on the
Nitrogen Cycle
   We add large amounts of nitric oxide (NO) into the
    atmosphere when N2 and O2 combine as we burn
    any fuel at high temperatures.
       This gas can be converted to nitrogen dioxide gas
        (NO2) and nitric acid (HNO3) which can return to
        the Earth’s surface as acid rain.
   We add nitrous oxide (N2O) to the atmosphere
    through the action of anaerobic bacteria on livestock
    wastes and commercial inorganic fertilizers applied
    to soil.
       This gas can warm the atmosphere and deplete
        ozone in the stratosphere.
Effects of Human Activities on the
    Nitrogen Cycle
   Nitrate ions in inorganic fertilizers can leach through
    the soil and contaminate groundwater.
       This is harmful to drink, especially for infants and small
        children.

   We release large quantities of nitrogen stored in
    soils and plants as gaseous compounds into the
    troposphere through destruction of forests,
    grasslands, and wetlands.
   We upset aquatic ecosystems by adding excess
    nitrates to bodies of water through agricultural runoff
    and discharges from municipal waste systems.
Effects of Human Activities on the
Nitrogen Cycle
   We remove nitrogen from topsoil when we harvest
    nitrogen-rich crops, irrigate crops, and burn or clear
    grasslands and forests before planting crops.
   Since 1950 human activities have more than
    doubled the annual release of nitrogen from the
    terrestrial portion of the earth into the rest of the
    environment.
   This is a serious local, regional, and global
    environmental problem that has attracted little
    attention when compared to global warming and
    depletion of the ozone layer.
The Phosphorus Cycle
   Phosphorus is a key component of DNA and energy storage
    molecules such as ATP in cells.
   Phosphorus circulates SLOWLY through water, the earth’s
    crust, and living organisms through the phosphorous cycle.
   On a human time scale, much phosphorus flows one-way
    from the land to the oceans.
   Phosphate is found as phosphate salts containing phosphate
    ions (PO43-) in terrestrial rock formations and ocean bottom
    sediments.
   As water runs over the phosphorus-containing rocks, it
    erodes away inorganic compounds that contain phosphate
    ions.
The Phosphorus Cycle
   Phosphate can be lost from the cycle for long
    periods of time when it washes from the land into
    streams and rivers and is carried to the ocean.
   Plants obtain phosphorus as phosphate ions
    directly from soil or water and incorporate it in
    various organic compounds.
   Animals get their phosphorous from plants and
    eliminate excess phosphorus in their urine.
   Most soils contain little phosphate so it is the
    limiting factor for plant growth on land unless
    phosphorus is applied to the soil as fertilizer.
mining       Fertilizer
excretion          Guano
                                                               agriculture
         uptake by weathering                           uptake by
        autotrophs                                     autotrophs
  Marine       Dissolved     leaching, runoff    Dissolved        Land
   Food         in Ocean                       in Soil Water,     Food
   Webs           Water                        Lakes, Rivers      Webs
           death,                                        death,
       decomposition                                decomposition
sedimentation       settling out              weathering
                               uplifting over
                               geologic time
     Marine Sediments                                     Rocks




                                                                  Fig. 3-31, p. 77
Effects of Human Activities on the
Phosphorous Cycle

   We mine large quantities of phosphate rock to
    make commercial inorganic fertilizers and
    detergents.
   We reduce the available phosphate in tropical
    soils when we cut down areas of tropical forests.
   We disrupt aquatic systems with phosphates
    from runoff of animal wastes and fertilizers and
    discharges from sewage treatment systems.
   Human activities have increased the natural rate
    of phosphorous about 3.7 times since 1900.
The Sulfur Cycle
   Sulfur circulates through the biosphere in the sulfur
    cycle.
   Much of the earth’s sulfur is stored underground in
    rocks and minerals, including sulfate (SO42-) salts
    buried deep under ocean sediments.
   Sulfur enters the atmosphere…
       As H2S and SO2 from volcanoes
       As particles of sulfate salts from sea spray, dust
        storms, and forest fires.
       When produced by marine algae as dimethyl sulfide
        (DMS).
Sulfur     Water                                                   Acidic fog and
                                     Sulfuric acid                                   precipitation
                 trioxide
                                             Ammonia       Ammonium
                   Oxygen                                  sulfate
Sulfur dioxide              Hydrogen sulfide

                                                                      Plants

  Dimethyl            Volcano
  sulfide                       Industries
                                                     Animals



Ocean


                                                                   Sulfate salts

                        Metallic               Decaying matter                          Sulfur
                        sulfide
                        deposits
                                                                 Hydrogen sulfide




                                                                                         Fig. 3-32, p. 78
Effects of Human Activities on the
Sulfur Cycle

   We burn sulfur-containing coal and oil to produce
    electric power.
   We refine sulfur containing petroleum to make
    gasoline, heating oil and other useful products.
   We convert sulfur-containing metallic mineral
    ores into free metals such as copper, lead, and
    zinc. This releases large amounts of sulfur
    dioxide into the environment.
The Gaia Hypothesis
Is the Earth alive?
The Gaia Hypothesis

    Some people have proposed that the Earth’s
     various forms of life control or at least
     influence its chemical cycles and other earth-
     sustaining processes.
    Named for the Greek goddess of the Earth.
    First proposed in 1979 by English inventor
     and atmospheric chemist James Lovelock
The Gaia Hypothesis

   Life controls the Earth’s life-sustaining
    processes. (Strong)


   Life influences the Earth’s life-sustaining
    processes. (Weak)


   The Earth is an incredibly complex system that
    sustains itself and adapts to changing
    environmental conditions to reach an optimal
    physical and chemical environment for life on
    this planet.
How Do Ecologists Learn About
Ecosystems?
   Ecologist go into ecosystems and learn what
    organisms live there and how they interact, use
    sensors on aircraft and satellites to collect data,
    and store and analyze geographic data in large
    databases.
       Field Research
       Geographic Information Systems
       Remote Sensing
   Ecologists use aquarium tanks, greenhouses,
    and controlled indoor and outdoor chambers to
    study ecosystems.
Geographic Information Systems
(GIS)

       A GIS organizes, stores, and analyzes
        complex data collected over broad
        geographic areas.
       Allows the simultaneous overlay of
        many layers of data.
Critical nesting site
                        locations



                       USDA Forest Service
             USDA
 Private Forest Service
 owner 1   Private owner 2

                             Topography




                             Habitat type
              Forest
Wetland Lake
           Grassland


                              Real world




                                                Fig. 3-33, p. 79
Systems Analysis
    Ecologists develop mathematical and other
     models to simulate the behavior of ecosystems.
    Can help us understand large and very complex
     systems (rivers, oceans, forests, grasslands,
     cities, and climate)
    Researchers can change values of the variables
     in their computer models to project possible
     changes in environmental conditions, help
     anticipate environmental surprises, and analyze
     the effectiveness of various alternative solutions
     to environmental problems.
Define objectives
  Systems
               Identify and inventory variables
Measurement
               Obtain baseline data on variables


               Make statistical analysis of
   Data        relationships among variables
  Analysis     Determine significant interactions



  System       Objectives Construct mathematical model
 Modeling      describing interactions among
               variables



  System       Run the model on a computer,
 Simulation    with values entered for different
               Variables



  System       Evaluate best ways to achieve
Optimization   objectives
                                               Fig. 3-34, p. 80
Importance of Baseline
Ecological Data
   We need baseline data on the world’s ecosystems so we
    can see how they are changing and develop effective
    strategies for preventing or slowing their degradation.
       Scientists have less than half of the basic ecological data
        needed to evaluate the status of ecosystems in the United
        Sates (Heinz Foundation 2002; Millennium Assessment
        2005).
All things come from
earth, and to earth
they all return.
Menander, 342 -290 BC

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Chapter 3

  • 1. Ecosystems: What Are They and How Do They Work? Chapter 3
  • 2. Learning Objectives  What is ecology?  What basic processes keep us and other organisms alive?  What are the major components of an ecosystem?  What happens to energy in an ecosystem?  What are soils and how are they formed?  What happens to matter in an ecosystem?  How do scientists study ecosystems?
  • 3. What is Ecology?  Ecology is …  the study of how organisms interact with each other and with their nonliving environment.  The study of connections in nature
  • 5. Organisms and Species  Organisms – Any form of life  Species – Groups of organisms that resemble one another in appearance, behavior, chemistry, and genetic makeup  There are 4 million to 100 million species on Earth.  Most known species are microorganisms that are too small to be seen with the naked eye.  10 million to 15 million other species  1.4 million species have been named (most are insects)
  • 6. Other animals Known species 281,000 1,412,000 Insects 751,000 Fungi 69,000 Prokaryotes 4,800 Plants 248,400 Protists 57,700 Fig. 3-3, p. 52
  • 7. Populations, Communities, & Ecosystems  Members of a species interact in groups called populations.  Populations of different species living and interacting in an area form a community.  A community interacting with its physical environment of matter and energy is an ecosystem.
  • 8.
  • 9. Universe Galaxies Solar systems Biosphere Planets Earth Biosphere Ecosystems Ecosystems Communities Populations Organisms Realm of ecology Communities Organ systems Organs Tissues Cells Protoplasm Populations Molecules Atoms Organisms Subatomic Particles Fig. 3-2, p. 51
  • 11. The Four Spheres  Earth is our life support system.  Earth is made up of interconnected spherical layers that contain air, water, soil, minerals, and life.  Atmosphere (air)  Hydrosphere (water)  Geosphere (rock)  Biosphere (living things)
  • 12.
  • 13. The Atmosphere  A thin envelope of air around the planet.  The atmosphere is divided into four layers based on temperature changes that occur at different distances above the Earth’s surface.  Troposphere  Stratosphere  Mesosphere  Thermosphere
  • 14.
  • 15. The Hydrosphere  Consists of earth’s water  Water can be found as liquid water, ice, and water vapor.  Liquid water: surface and underground  Ice: polar ice, icebergs, permafrost  Water Vapor: gas in the atmosphere
  • 16. The Geosphere  The Earth can also be divided into layers based on physical properties or chemical properties.  3 Layers (Chemical Properties):  Crust  Mantle  Core  5 Layers (Physical Properties):  Lithosphere  Asthenosphere  Mesosphere  Outer Core  Inner Core
  • 17.
  • 18. The Biosphere  All of Earth’s living things.  All of Earth’s ecosystems together.
  • 19. Everything is linked to everything else.
  • 21. 3 Interconnected Forces  Solar Energy  The Cycling of Matter  Gravity
  • 22. Biosphere Carbon Phosphorus Nitrogen Water Oxygen cycle cycle cycle cycle cycle Heat in the environment Heat Heat Heat Fig. 3-7, p. 55
  • 23. Solar Energy  The flow of high-quality energy from the sun through materials and living things in their feeding interactions, into the environment as low-quality energy, and eventually back into space as heat.  Solar energy flows through the biosphere, warms the atmosphere, evaporates and recycles water, generates winds, and supports plant growth.
  • 24. Solar Energy  About one-billionth of the sun’s output of energy reaches the earth.  Much of the energy is reflected away or absorbed by the chemicals, dust, and clouds in the atmosphere.
  • 25. Solar radiation Energy in = Energy out Reflected by atmosphere (34% ) Radiated by UV radiation atmosphere as heat (66%) Lower Stratosphere Absorbed (ozone layer) by ozone Visible Troposphere Greenhouse Light effect Heat Absorbed by the Heat radiated earth by the earth Fig. 3-8, p. 55
  • 27. Biomes and Aquatic Life Zones  Life exists on land systems called biomes and in freshwater and ocean aquatic life zones.  Biome = The terrestrial portion of the biosphere.  Aquatic Life Zones = Water parts of the biosphere
  • 28. Biotic and Abiotic Factors  Ecosystems consist of nonliving and living components.  Biotic = living components  Producers  Consumers  Decomposers  Abiotic = nonliving components
  • 29. Oxygen Sun (O2) Producer Carbon dioxide (CO2) Secondary consumer Primary (fox) consumer (rabbit) Precipitation Producers Falling leaves and twigs Soil decomposers Water Fig. 3-10, p. 57
  • 30. Factors that Limit Population Growth  Different species and their populations thrive under different physical and chemical conditions.  Availability of matter and energy can limit the number of organisms in a population.  Limiting Factor Principle = Too much or too little of any abiotic factor can limit or prevent growth of a population, even if all other factors are at or near the optimum range of tolerance.  Precipitation/Amount of Water  Soil nutrients  Temperature  Sunlight  Salinity  Dissolved Oxygen Content
  • 31.
  • 32. Producers (Autotrophs)  Some organisms in ecosystems can produce the food they need from chemicals in their environment.  Photosynthesis  Chemosynthesis
  • 33. Consumers (Heterotrophs)  Consumers get their food by eating or breaking down all or parts of other organisms or their remains.  Herbivores/Primary Consumers – eat producers  Carnivores/Secondary Consumers – eat herbivores  Tertiary Consumers – eat other carnivores  Omnivores – eat both plants and animals
  • 34. Decomposers and Detritrivores  Decomposers  Specialized organisms that recycle nutrients in ecosystems.  Digest or degrade living or dead organisms into simpler inorganic compounds that producers can take up form soil and water to use as nutrients.  Detritrivores  Insects and other scavengers that feed on the wastes or dead bodies of other organisms.
  • 35. Scavengers Decomposers Termite Bark beetle Carpenter and engraving ant carpenter Long- horned galleries ant work Dry rot fungus beetle holes Wood reduced to Mushroom powder Time Powder broken down by decomposers progression into plant nutrients in soil Fig. 3-13, p. 61
  • 36. Energy Flow in Ecosystems
  • 37. Food Chains and Food Webs  Food chains and webs show how eaters, the eaten, and the decomposed are connected to one another in an ecosystem.  All organisms, whether dead or alive, are potential sources of food for other organisms.  There is little matter wasted in natural ecosystems.  Trophic Levels = Feeding Levels
  • 38. First Trophic Second Trophic Third Trophic Fourth Trophic Level Level Level Level Producers Primary Secondary Tertiary (plants) consumers consumers consumers (herbivores) (carnivores) (top carnivores) Heat Heat Heat Solar energy Heat Heat Heat Heat Detritivores Heat (decomposers and detritus feeders) Fig. 3-17, p. 64
  • 39. Blue whale Humans Sperm whale Crabeater Elephant seal seal Killer whale Leopard seal Adelie penguins Emperor penguin Squid Petrel Fish Carnivorous plankton Krill Herbivorous plankton Phytoplankton Fig. 3-18, p. 65
  • 40. Losing Energy in Food Chains and Webs  There is a decrease in the amount of energy available to each succeeding organisms in a food chain or web. (2nd Law of Thermodynamics)  Each trophic level contains a certain amount of biomass.  Only a small portion of what is eaten and digested is actually converted into an organism’s biomass.  The amount available to each successive trophic level declines.
  • 41. Ecological Efficiency  The percentage of usable energy transferred as biomass from one trophic level to the next.  It ranges from 2% to 40% or a loss of 60% to 98%.  10% ecological efficiency is typical
  • 42. Heat Tertiary Heat consumers Decomposers (human) Heat 10 Secondary consumers (perch) Heat 100 Primary 1,000 consumers (zooplankton) Heat 10,000 Producers Usable energy (phytoplankton) Available at Each tropic level (in kilocalories) Fig. 3-19, p. 66
  • 43. Ecological Efficiency  Energy flow pyramids explain why the Earth can support more people if they eat at lower trophic levels by consuming grains, vegetables, and fruits.  Food chains and webs rarely have more than four or five trophic levels.
  • 45. Biodiversity  A vital renewable resource is the biodiversity found in the earth’s variety of genes, species, ecosystems, and ecosystem processes.  4 Components  Functional Diversity  Ecological Diversity  Species Diversity  Genetic Diversity
  • 46. Functional Diversity The biological and chemical processes such as energy flow and matter recycling needed for the survival of species, communities and ecosystems.
  • 47. Ecological Diversity The variety of terrestrial and aquatic ecosystems found in an area or on the earth.
  • 48. Species Diversity The number of species present in different habitats.
  • 49. Genetic Diversity The variety of genetic material within a species or population.
  • 50. Biodiversity Loss and Species Extinction  Human activities are destroying and degrading the habitats for many wild species and driving some of them to premature extinction.  Sooner or later all species become extinct because they cannot respond successfully to changing environmental conditions.  Current extinction rates are 100 to 10,000 times higher than natural extinction rates because of human activities.
  • 51. Biodiversity Loss and Species Extinction H = Habitat destruction and degradation I = Invasive species P = Pollution P = human Population growth O = Overexploitation (overhunting, over consumption)
  • 52. Why Should We Care About Biodiversity?  Biodiversity provides us with:  Natural Resources (food water, wood, energy, and medicines)  Natural Services (air and water purification, soil fertility, waste disposal, pest control)  Aesthetic pleasure
  • 53.
  • 54. In-Class Assignment 1. Read the Core Case Study on page 50. 2. Summarize the importance of insects in the earth’s biodiversity. 3. Share with the class.
  • 55. Solutions  Goals, strategies and tactics for protecting biodiversity. Figure 3-16
  • 56. Soil: A Renewable Resource
  • 57. What is Soil? Why is it Important?  Soil is a slowly renewed resource that provides most of the nutrients needed for plant growth and also helps purify water.  Soil is a thin covering over most land that is a complex mixture of eroded rock, mineral nutrients, decaying organic matter, water, air, and living organisms.  Soil forms when rock is broken down into fragments and particles by physical, chemical, and biological weathering.
  • 58. What is Soil? Why is it Important?  Over hundreds to thousands of years various types of life build up layers of inorganic and organic matter on soil’s original bedrock.  Formation of 1 cm of soil can take from 15 years to hundreds of years.  Soil is the base of life on land.  Producers get the nutrients they need from soil and water.  You are mostly composed of soil nutrients imported into your body by the food you eat.
  • 59. What is Soil? Why is it Important?  Soil helps cleanse water that flows through it.  Soil helps decompose and recycle biodegradable wastes.  Soil helps remove carbon dioxide from the atmosphere and stores it as carbon compounds.
  • 60. Mature Soils  Soils that have developed over a long time.  Arranged in soil horizons, each has a distinct texture and composition.  Soil Profile – a cross-sectional view of the horizons in a soil.  Most mature soils have at least three of the possible horizons.
  • 61. Wood Oak tree sorrel Lords and Dog violet Organic debris ladies Grasses and builds up Rock small shrubs fragments Earthworm Fern Millipede Moss and Honey fungus lichen O horizon Mole Leaf litter A horizon Topsoil B horizon Bedrock Subsoil Immature soil Regolith C horizon Young soil Pseudoscorpion Parent Mite material Nematode Root system Actinomycetes Red Earth Mite Fungus Mature soil Bacteria Springtail Fig. 3-23, p. 68
  • 62. Soil Layers  O Horizon – Surface Litter Layer  Freshly fallen or partially decomposed leaves  Twigs  Crop wastes  Animal Wastes  Normally brown or black
  • 63. Soil Layers  A Horizon – Topsoil  Porous mixture of partially decomposed bodies of dead plants and animals (Humus)  Inorganic materials such as clay, silt, sand  Fertile soil that produces high crop yields has a thick topsoil layer with lots of humus.  Helps topsoil hold water and nutrients taken up by plant roots.
  • 64. Soil Layers  2 Upper Layers  Most plant roots and organic matter are located here  As long as vegetation anchors these layers, the soil will hold water and release it as needed  Full of bacteria, fungi, earthworms, and small insects  The color of topsoil is a clue to its ability to grow crops.  Dark brown or black = rich in nitrogen and organic matter  Gray, yellow, red = low in nitrogen and organic matter.
  • 65. Soil Layers  B Horizon – Subsoil and C Horizon – Parent material  Contain most inorganic matter  Broken down rock  Transported by water from the A horizon
  • 66. Wood Oak tree sorrel Lords and Dog violet Organic debris ladies Grasses and builds up Rock small shrubs fragments Earthworm Fern Millipede Moss and Honey fungus lichen O horizon Mole Leaf litter A horizon Topsoil B horizon Bedrock Subsoil Immature soil Regolith C horizon Young soil Pseudoscorpion Parent Mite material Nematode Root system Actinomycetes Red Earth Mite Fungus Mature soil Bacteria Springtail Fig. 3-23, p. 68
  • 67. Soil  The spaces (pores) between the solid organic and inorganic particles contain air and water.  Plants need the oxygen for cellular respiration.  Precipitation that reaches the soil percolates through the soil layers and occupies many of the soil’s open spaces or pores. (Infiltration)  As the water seeps down it dissolves various minerals and organic matter in the upper layers and carries them to lower layers. (leaching)
  • 68. Soil Properties  Soils vary in the size of the particles they contain, the amount of space between these particles, and how rapidly water flows through them.  Clay – Very small particles  Silt – Medium particles  Sand – Largest particles  Soil Texture – The relative amounts of the different sizes and types of these mineral particles.
  • 69. Sand Silt Clay 0.05–2 mm 0.002–0.05 mm less than 0.002 mm diameter diameter Diameter Water Water High permeability Low permeability Fig. 3-25, p. 70
  • 70. Mosaic of closely packed pebbles, boulders Weak humus- mineral mixture Alkaline, dark, Dry, brown to and rich reddish-brown in humus with variable accumulations Clay, of clay, calcium calcium and carbonate, compounds and soluble Desert Soil Grassland Soil salts (hot, dry climate) semiarid climate) Fig. 3-24a, p. 69
  • 71. Acidic light-colored humus Iron and aluminum compounds mixed with clay Tropical Rain Forest Soil (humid, tropical climate) Fig. 3-24b, p. 69
  • 72. Forest litter leaf mold Humus-mineral mixture Light, grayish- brown, silt loam Dark brown firm clay Deciduous Forest Soil (humid, mild climate) Fig. 3-24b, p. 69
  • 73. Acid litter and humus Light-colored and acidic Humus and iron and aluminum compounds Coniferous Forest Soil (humid, cold climate) Fig. 3-24b, p. 69
  • 75. Nutrient Cycles: Global Recycling  Global cycles recycle nutrients through the earth’s air, land, water, and living organisms and, in the process, connect past, present, and future forms of life.  Nutrients –the elements and compounds that organisms need to live, grow, and reproduce  Biogeochemical Cycles  Water  Carbon  Nitrogen  Phosphorus  Sulfur
  • 76. The Water Cycle  A vast global cycle collects, purifies, distributes, and recycles the Earth’s fixed supply of water.  Also called the hydrologic cycle.  Powered by energy from the sun and by gravity.  84% of water vapor in the atmosphere comes from oceans.  Most precipitation becomes surface runoff
  • 77. Water’s Unique Properties  There are strong forces of attraction between molecules of water.  Water exists as a liquid over a wide temperature range.  Liquid water changes temperature slowly.  It takes a large amount of energy for water to evaporate.  Liquid water can dissolve a variety of compounds.  Water expands when it freezes.
  • 78. Rain clouds Condensation Transpiration Evaporation Precipitation Transpiration to land from plants Precipitation Precipitation Evaporation Surface runoff from land Evaporation Runoff from ocean Precipitation (rapid) to ocean Infiltration and Surface Percolation runoff (rapid) Groundwater movement (slow) Ocean storage Fig. 3-26, p. 72
  • 79. Surface Run Off  Replenishes streams and lakes  Causes soil erosion  Sculpts the landscape  Transports nutrients
  • 80. Effects of Human Activities on the Water Cycle  We alter the water cycle by…  Withdrawing large amounts of fresh water  Clearing vegetation and eroding soils  Polluting surface and underground water  Contributing to climate change
  • 81. The Carbon Cycle  Carbon cycles through the earth’s air, water, soil, and living organisms and depends on photosynthesis and respiration.  Carbon is the basic building block of the carbohydrates, fats, proteins, DNA, and other organic compounds necessary for life.  The carbon cycle is based on carbon dioxide (CO2)
  • 82. Fig. 3-27, pp. 72-73
  • 83. The Carbon Cycle: Earth’s Thermostat  If the carbon cycle removes too much CO2 from the atmosphere, the atmosphere will cool.  If the carbon cycle generates too much CO2 the atmosphere will get warmer.  Even slight changes in the cycle can affect climate and help determine the types of life that can exist on various parts of the Earth.
  • 84. The Carbon Cycle: How it Works  Terrestrial producers remove CO2 from the atmosphere.  Aquatic producers remove CO2 from the water.  All producers use photosynthesis to convert CO2 into complex carbohydrates (like glucose)  The cells in consumers carry out aerobic respiration. They break down glucose and convert the glucose back to CO2 for reuse by consumers.  The link between photosynthesis and aerobic respiration circulates carbon in the biosphere.
  • 85. The Carbon Cycle: How it Works  Some carbon atoms take a long time to recycle.  Over millions of years, buried deposits of dead plant matter and bacteria are compressed between layers of sediment, where they form carbon-containing fossil fuels.  This carbon is not released to the atmosphere as CO2 for recycling until these fuels are extracted and burned.  In the past 50 years, we have extracted and burned fossil fuels that took millions of years to form.
  • 86. The Carbon Cycle: The Role of Oceans  Some of the atmosphere’s carbon dioxide dissolves in ocean water and the ocean’s photosynthesizing producers remove some.  As the ocean water warms, some of the dissolved CO2 returns to the atmosphere  Some ocean organisms build their shells and skeletons by using dissolved CO2 molecules.
  • 87. Effects of Human Activities on the Carbon Cycle  We alter the carbon cycle by…  Clear trees and plants that absorb CO2 through photosynthesis faster than they can grow back  Add large amounts of CO2 by burning fossil fuels and wood.  Increased concentrations of can enhance the planet’s natural greenhouse effect.  Global warming disrupts global food production and wildlife habitats, alter temperature and precipitation patterns, and raise the average sea level in various parts of the world.
  • 88. CO2 emissions from fossil fuels (billion metric tons of carbon equivalent) Year Low projection High projection Fig. 3-28, p. 74
  • 89. The Nitrogen Cycle  Different types of bacteria help recycle nitrogen through the Earth’s air, water, soil and living organisms.  Nitrogen is…  The most abundant gas in the atmosphere  Crucial component of proteins, vitamins, nucleic acids  N2 cannot be absorbed and used directly as a nutrient by multicellular plants or animals.
  • 90. The Nitrogen Cycle  Two natural processes fix N2 into useful compounds  Lightning  Nitrogen Cycle  Nitrogen-fixing bacteria in soil and aquatic environments convert (fix) gaseous nitrogen (N2 ) into ammonia (NH3) which is later converted into ammonium ions (NH4+) that can be used by plants.  Ammonia not taken up by plants undergoes nitrification. Specialized soil bacteria convert the NH3 and NH4+ into nitrite ions (NO2-) which are toxic to plants, and then to nitrate (NO3-) ions which are taken up by the roots of plants.  Animals get their nitrogen by eating plants or plant-eating animals.
  • 91. The Nitrogen Cycle  Plants and animals return nitrogen-rich organic compounds to the environment as wastes, cast-off particles, and through their bodies when they die.  In ammonificiation, large numbers of specialized decomposer bacteria convert organic material into simple nitrogen-containing inorganic compounds such as ammonia (NH3) and water-soluble salts containing ammonium ions (NH4+).  In denitrification, nitrogen leaves the soil as specialized bacteria in waterlogged soil and in the bottom sediments of lakes, oceans, swamps, and bogs to convert NH3 and NH4+ back into nitrite and nitrate ions, then into nitrogen gas (N2) and nitrous oxide gas (N2O). These gases are released to the atmosphere to begin the nitrogen cycle again.
  • 92. Gaseous nitrogen (N2) in atmosphere Food webs on land Nitrogen fixation Fertilizers Uptake by Loss by Uptake by autotrophs Excretion, death, autotrophs denitrification decomposition Ammonia, ammonium in soil Nitrogen-rich wastes, Nitrate in soil remains in soil Nitrification Ammonification Loss by Loss by leaching leaching Nitrite in soil Nitrification Fig. 3-29, p. 75
  • 93. Effects of Human Activities on the Nitrogen Cycle  We add large amounts of nitric oxide (NO) into the atmosphere when N2 and O2 combine as we burn any fuel at high temperatures.  This gas can be converted to nitrogen dioxide gas (NO2) and nitric acid (HNO3) which can return to the Earth’s surface as acid rain.  We add nitrous oxide (N2O) to the atmosphere through the action of anaerobic bacteria on livestock wastes and commercial inorganic fertilizers applied to soil.  This gas can warm the atmosphere and deplete ozone in the stratosphere.
  • 94. Effects of Human Activities on the Nitrogen Cycle  Nitrate ions in inorganic fertilizers can leach through the soil and contaminate groundwater.  This is harmful to drink, especially for infants and small children.  We release large quantities of nitrogen stored in soils and plants as gaseous compounds into the troposphere through destruction of forests, grasslands, and wetlands.  We upset aquatic ecosystems by adding excess nitrates to bodies of water through agricultural runoff and discharges from municipal waste systems.
  • 95. Effects of Human Activities on the Nitrogen Cycle  We remove nitrogen from topsoil when we harvest nitrogen-rich crops, irrigate crops, and burn or clear grasslands and forests before planting crops.  Since 1950 human activities have more than doubled the annual release of nitrogen from the terrestrial portion of the earth into the rest of the environment.  This is a serious local, regional, and global environmental problem that has attracted little attention when compared to global warming and depletion of the ozone layer.
  • 96. The Phosphorus Cycle  Phosphorus is a key component of DNA and energy storage molecules such as ATP in cells.  Phosphorus circulates SLOWLY through water, the earth’s crust, and living organisms through the phosphorous cycle.  On a human time scale, much phosphorus flows one-way from the land to the oceans.  Phosphate is found as phosphate salts containing phosphate ions (PO43-) in terrestrial rock formations and ocean bottom sediments.  As water runs over the phosphorus-containing rocks, it erodes away inorganic compounds that contain phosphate ions.
  • 97. The Phosphorus Cycle  Phosphate can be lost from the cycle for long periods of time when it washes from the land into streams and rivers and is carried to the ocean.  Plants obtain phosphorus as phosphate ions directly from soil or water and incorporate it in various organic compounds.  Animals get their phosphorous from plants and eliminate excess phosphorus in their urine.  Most soils contain little phosphate so it is the limiting factor for plant growth on land unless phosphorus is applied to the soil as fertilizer.
  • 98. mining Fertilizer excretion Guano agriculture uptake by weathering uptake by autotrophs autotrophs Marine Dissolved leaching, runoff Dissolved Land Food in Ocean in Soil Water, Food Webs Water Lakes, Rivers Webs death, death, decomposition decomposition sedimentation settling out weathering uplifting over geologic time Marine Sediments Rocks Fig. 3-31, p. 77
  • 99. Effects of Human Activities on the Phosphorous Cycle  We mine large quantities of phosphate rock to make commercial inorganic fertilizers and detergents.  We reduce the available phosphate in tropical soils when we cut down areas of tropical forests.  We disrupt aquatic systems with phosphates from runoff of animal wastes and fertilizers and discharges from sewage treatment systems.  Human activities have increased the natural rate of phosphorous about 3.7 times since 1900.
  • 100. The Sulfur Cycle  Sulfur circulates through the biosphere in the sulfur cycle.  Much of the earth’s sulfur is stored underground in rocks and minerals, including sulfate (SO42-) salts buried deep under ocean sediments.  Sulfur enters the atmosphere…  As H2S and SO2 from volcanoes  As particles of sulfate salts from sea spray, dust storms, and forest fires.  When produced by marine algae as dimethyl sulfide (DMS).
  • 101. Sulfur Water Acidic fog and Sulfuric acid precipitation trioxide Ammonia Ammonium Oxygen sulfate Sulfur dioxide Hydrogen sulfide Plants Dimethyl Volcano sulfide Industries Animals Ocean Sulfate salts Metallic Decaying matter Sulfur sulfide deposits Hydrogen sulfide Fig. 3-32, p. 78
  • 102. Effects of Human Activities on the Sulfur Cycle  We burn sulfur-containing coal and oil to produce electric power.  We refine sulfur containing petroleum to make gasoline, heating oil and other useful products.  We convert sulfur-containing metallic mineral ores into free metals such as copper, lead, and zinc. This releases large amounts of sulfur dioxide into the environment.
  • 103. The Gaia Hypothesis Is the Earth alive?
  • 104. The Gaia Hypothesis  Some people have proposed that the Earth’s various forms of life control or at least influence its chemical cycles and other earth- sustaining processes.  Named for the Greek goddess of the Earth.  First proposed in 1979 by English inventor and atmospheric chemist James Lovelock
  • 105. The Gaia Hypothesis  Life controls the Earth’s life-sustaining processes. (Strong)  Life influences the Earth’s life-sustaining processes. (Weak)  The Earth is an incredibly complex system that sustains itself and adapts to changing environmental conditions to reach an optimal physical and chemical environment for life on this planet.
  • 106. How Do Ecologists Learn About Ecosystems?  Ecologist go into ecosystems and learn what organisms live there and how they interact, use sensors on aircraft and satellites to collect data, and store and analyze geographic data in large databases.  Field Research  Geographic Information Systems  Remote Sensing  Ecologists use aquarium tanks, greenhouses, and controlled indoor and outdoor chambers to study ecosystems.
  • 107. Geographic Information Systems (GIS)  A GIS organizes, stores, and analyzes complex data collected over broad geographic areas.  Allows the simultaneous overlay of many layers of data.
  • 108. Critical nesting site locations USDA Forest Service USDA Private Forest Service owner 1 Private owner 2 Topography Habitat type Forest Wetland Lake Grassland Real world Fig. 3-33, p. 79
  • 109. Systems Analysis  Ecologists develop mathematical and other models to simulate the behavior of ecosystems.  Can help us understand large and very complex systems (rivers, oceans, forests, grasslands, cities, and climate)  Researchers can change values of the variables in their computer models to project possible changes in environmental conditions, help anticipate environmental surprises, and analyze the effectiveness of various alternative solutions to environmental problems.
  • 110. Define objectives Systems Identify and inventory variables Measurement Obtain baseline data on variables Make statistical analysis of Data relationships among variables Analysis Determine significant interactions System Objectives Construct mathematical model Modeling describing interactions among variables System Run the model on a computer, Simulation with values entered for different Variables System Evaluate best ways to achieve Optimization objectives Fig. 3-34, p. 80
  • 111. Importance of Baseline Ecological Data  We need baseline data on the world’s ecosystems so we can see how they are changing and develop effective strategies for preventing or slowing their degradation.  Scientists have less than half of the basic ecological data needed to evaluate the status of ecosystems in the United Sates (Heinz Foundation 2002; Millennium Assessment 2005).
  • 112. All things come from earth, and to earth they all return. Menander, 342 -290 BC