ECOSYSTEMS

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CHAPTER 55

• ECOSYSTEMS

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A terrarium, an example of an ecosystem
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The Ecosystem

• All organisms living in a given area and the
• abiotic factors with which they interact. It is
• a community with certain unique characteristics.
• Boundaries are usually not discrete.
• Most inclusive level of biological
  organization.
• Involves energy flow and nutrient cycling.

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THE ECOSYSTEM

• Trophic Levels
• Primary Producers - Autotrophs
• Consumers - Heterotrophs
• Primary - Herbivores
• Secondary - Carnivores
• Tertiary Carnivores or Omnivores
• Decomposers Detritivores

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Figure 54.2 Fungi decomposing a log
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Energy Flow
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Primary Productivity

• Gross Primary Productivity
• Amount of light energy that is converted into
  chemical energy by autotrophs in a given time
  period.
• Net Primary Productivity NPP GPP - R
• To come
• Global energy budget
• Fraction of solar energy used in
  photosynthesis

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Primary Productivity

• 1022 joules/day
• The Amount of Solar Energy Converted to
  Chemical Energy. 1 of Visible Light That
• Reaches Photosynthetic Organisms.
• Gross Primary Productivity (GPP) 170 Billion
  Tons/yr.
• Net Primary Productivity -
• Measured Biomass or Energy
• g/m2/yr or J/m2/yr
• Standing Crop

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Primary Productivity

• Ecosystem Variation
• Marine Ecosystems
• Limiting factor
• Sunlight and nutrients
• Upwellings
• Fresh Water Ecosystems
• Nutrients
• Light and Depth
• Turnover
• Eutrophication
• Terrestrial
• Nutrients, evapotranspiration..

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Inorganic Nutrients

• Common Limiting Factors
• Macronutrients
• Nitrogen
• Phosphorous
• Micronutrients
• Iron

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Fig. 55-7
EXPERIMENT
Long Island
Shinnecock Bay
G
F
E
C
D
Moriches Bay
B
Great South Bay
Atlantic Ocean
A
RESULTS
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Ammonium enriched
Phosphate enriched
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Unenriched control
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Phytoplankton density (millions of cells per mL)
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6
0
A
B
C
D
E
F
G
Collection site
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Table 55-1
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Primary Productivity

• Terrestrial Ecosystems
• Limiting Factors
• Actual Evapotranspiration

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Nutrients as Limiting Factors
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Fig. 55-6
Net primary production (kg carbon/m2yr)

0
1
2
3
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• Tropical rain forests, estuaries, and coral reefs
  are among the most productive ecosystems per unit
  area
• Marine ecosystems are relatively unproductive per
  unit area, but contribute much to global net
  primary production because of their volume

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Figure 54.3 Primary production of different
ecosystems
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Energy Transfer and Partitioning

• Efficiency usually less than 20, average of
  10.
• Secondary Production

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ECOLOGICAL PYRAMID
Energy flows through the ecosystem, not cycled
5 to 20 Efficiency Average 10 Efficiency in
Energy Transfer From Trophic Level to Trophic
Level.
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ECOLOGICAL PYRAMID

• Pyramids of Productivity
• Pyramids of Biomass
• Pyramids of Numbers

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Figure 54.11 An idealized pyramid of net
production
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Figure 54.12 Pyramids of biomass (standing crop)
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• Certain aquatic ecosystems have inverted biomass
  pyramids producers (phytoplankton) are consumed
  so quickly that they are outweighed by primary
  consumers
• Turnover time is a ratio of the standing crop
  biomass to production

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Energy Flow and Man

• Dynamics of energy flow in ecosystems have
  important implications for the human population
• Eating meat is a relatively inefficient way of
  tapping photosynthetic production
• Worldwide agriculture could feed many more people
  if humans ate only plant material
• Most terrestrial ecosystems have large standing
  crops despite the large numbers of herbivores

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Fig. 55-12
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Green Earth Hypothesis

• Why is the Earth so green?
• Herbivores held in check by Plant defenses
• Nutrient supply limited to herbivores
• Unfavorable abiotic factors
• Interspecific competition
• Interspecific interactions predation,
  parasitism, disease

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Cycling of Chemical Elements

• Biogeochemical Cycles
• Continuing Processes
• Decomposition Necessary for Inorganic
  Nutrients
• C, O, S, N Gaseous Cycles
• P, K, Ca Substrate Cycles
• Limestone
• Erosion
• Weathering

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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

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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
• A model of nutrient cycling includes main
  reservoirs of elements and processes that
  transfer elements between reservoirs
• All elements cycle between organic and inorganic
  reservoirs

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• In studying cycling of water, carbon, nitrogen,
  and phosphorus, ecologists focus on four factors
• Each chemicals biological importance
• Forms in which each chemical is available or used
  by organisms
• Major reservoirs for each chemical
• Key processes driving movement of each chemical
  through its cycle

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• The Water Cycle
• Water is essential to all organisms
• 97 of the biospheres water is contained in the
  oceans, 2 is in glaciers and polar ice caps, and
  1 is in lakes, rivers, and groundwater
• Water moves by the processes of evaporation,
  transpiration, condensation, precipitation, and
  movement through surface and groundwater

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Fig. 55-14a
Transport over land
Solar energy
Net movement of water vapor by wind
Precipitation over land
Evaporation from ocean
Precipitation over ocean
Evapotranspiration from land
Percolation through soil
Runoff and groundwater
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• The Carbon Cycle
• Carbon-based organic molecules are essential to
  all organisms
• Carbon reservoirs include fossil fuels, soils and
  sediments, solutes in oceans, plant and animal
  biomass, and the atmosphere
• CO2 is taken up and released through
  photosynthesis and respiration additionally,
  volcanoes and the burning of fossil fuels
  contribute CO2 to the atmosphere

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Fig. 55-14b
CO2 in atmosphere
Photosynthesis
Cellular respiration
Photo- synthesis
Burning of fossil fuels and wood
Phyto- plankton
Higher-level consumers
Primary consumers
Carbon compounds in water
Detritus
Decomposition
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• The Terrestrial Nitrogen Cycle
• Nitrogen is a component of amino acids, proteins,
  and nucleic acids
• The main reservoir of nitrogen is the atmosphere
  (N2), though this nitrogen must be converted to
  NH4 or NO3 for uptake by plants, via nitrogen
  fixation by bacteria

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• Organic nitrogen is decomposed to NH4 by
  ammonification, and NH4 is decomposed to NO3 by
  nitrification
• Denitrification converts NO3 back to N2

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Fig. 55-14c
N2 in atmosphere
Assimilation
Denitrifying bacteria
NO3

Nitrogen-fixing bacteria
Decomposers
Nitrifying bacteria
Ammonification
Nitrification
NH3
NH4
NO2


Nitrogen-fixing soil bacteria
Nitrifying bacteria
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• The Phosphorus Cycle
• Phosphorus is a major constituent of nucleic
  acids, phospholipids, and ATP
• Phosphate (PO43) is the most important inorganic
  form of phosphorus
• The largest reservoirs are sedimentary rocks of
  marine origin, the oceans, and organisms
• Phosphate binds with soil particles, and movement
  is often localized

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Fig. 55-14d
Precipitation
Geologic uplift
Weathering of rocks
Runoff
Consumption
Decomposition
Plant uptake of PO43
Plankton
Dissolved PO43
Soil
Uptake
Leaching
Sedimentation
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Decomposition and Nutrient Cycling Rates

• Decomposers (detritivores) play a key role in the
  general pattern of chemical cycling
• Rates at which nutrients cycle in different
  ecosystems vary greatly, mostly as a result of
  differing rates of decomposition
• The rate of decomposition is controlled by
  temperature, moisture, and nutrient availability
• Rapid decomposition results in relatively low
  levels of nutrients in the soil

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Figure 54.21 Hubbard Brook Experimental Forest
Concrete dams (left), logged watersheds (right)
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Fig. 55-16b
(b) Clear-cut watershed
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Figure 54.21c Nutrient cycling in the Hubbard
Brook Experimental Forest an example of
long-term ecological research
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Concept 55.5 Human activities now dominate most
chemical cycles on Earth

• As the human population has grown, our activities
  have disrupted the trophic structure, energy
  flow, and chemical cycling of many ecosystems
• In addition to transporting nutrients from one
  location to another, humans have added new
  materials, some of them toxins, to ecosystems

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Agriculture and Nitrogen Cycling

• The quality of soil varies with the amount of
  organic material it contains
• Agriculture removes from ecosystems nutrients
  that would ordinarily be cycled back into the
  soil
• Nitrogen is the main nutrient lost through
  agriculture thus, agriculture greatly affects
  the nitrogen cycle
• Industrially produced fertilizer is typically
  used to replace lost nitrogen, but effects on an
  ecosystem can be harmful

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Agricultural Impact on Soil Nutrients
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Fig. 55-17
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Contamination of Aquatic Ecosystems

• Critical load for a nutrient is the amount that
  plants can absorb without damaging the ecosystem
• When excess nutrients are added to an ecosystem,
  the critical load is exceeded
• Remaining nutrients can contaminate groundwater
  as well as freshwater and marine ecosystems
• Sewage runoff causes cultural eutrophication,
  excessive algal growth that can greatly harm
  freshwater ecosystems

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Fig. 55-18
Winter
Summer
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Acid Precipitation

• Combustion of fossil fuels is the main cause of
  acid precipitation
• North American and European ecosystems downwind
  from industrial regions have been damaged by rain
  and snow containing nitric and sulfuric acid
• Acid precipitation changes soil pH and causes
  leaching of calcium and other nutrients

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Fig. 55-19
4.5
4.4
4.3
pH
4.2
4.1
4.0
2000
1995
1990
1985
1980
1975
1970
1965
1960
Year
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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

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Figure 54.24 Weve changed our tune
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Figure 54.25 Biological magnification of DDT in
a food chain
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Biological Magnification
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Greenhouse Gases and Global Warming

• One pressing problem caused by human activities
  is the rising level of atmospheric carbon dioxide

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Fig. 55-21
14.9
390
14.8
380
14.7
14.6
370
Temperature
14.5
360
14.4
14.3
350
CO2 concentration (ppm)
Average global temperature (ºC)
14.2
340
14.1
CO2
330
14.0
13.9
320
13.8
310
13.7
13.6
300
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
Year
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Fig. 55-22
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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

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Fig. 55-23
350
300
250
Ozone layer thickness (Dobsons)
200
100
0
80
60
05
2000
95
90
85
75
70
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1955
Year
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• Destruction of atmospheric ozone probably results
  from chlorine-releasing pollutants such as CFCs
  produced by human activity
• Scientists first described an ozone hole over
  Antarctica in 1985 it has increased in size as
  ozone depletion has increased

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Fig. 55-25
(a) September 1979
(b) September 2006
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• Ozone depletion causes DNA damage in plants and
  poorer phytoplankton growth
• An international agreement signed in 1987 has
  resulted in a decrease in ozone depletion