Dynamics of Ecosystems Chapter 57

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Dynamics of EcosystemsChapter 57
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Biogeochemical Cycles

• Ecosystem includes all the organisms that live
  in a particular place, plus the abiotic
  environment in which they live and interact
• Biological processing of matter cycling of
  atoms in the environment and in living organisms
• Biogeochemical cycles chemicals moving through
  ecosystems biotic and abiotic

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Biogeochemical Cycles

• Biogeochemical cycles usually cross the
  boundaries of ecosystem
• One ecosystem might import or export chemicals to
  another
• Carbon is a major constituent of the bodies of
  organisms
• 20 of weight of human body is carbon
• Makes up 0.03 volume of the atmosphere 750
  billion metric tons

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Biogeochemical Cycles

• The carbon cycle

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Biogeochemical Cycles

• Carbon fixation metabolic reactions that make
  nongaseous compounds from gaseous ones
• In aquatic systems inorganic carbon is present in
  water as dissolved CO2 and as HCO3- ions
• CO2 is used by algae and aquatic plants for
  photosynthesis (make glucose)

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Biogeochemical Cycles

• Methane producers
• Microbes that break down organic compounds by
  anaerobic cellular respiration provide an
  additional dimension to the carbon cycle
• Methanogens produce methane (CH4)
• Wetland ecosystems are a source of CH4
• CH4 is oxidized to CO2, but can remain as CH4 for
  a long time

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Biogeochemical Cycles

• Over time, globally, the carbon cycle may proceed
  faster in one direction
• This can cause large consequences if continued
  for many years
• Earths present preserves of coal, and other
  fossil fuels were built up over geological time
• Human burning of fossil fuels is creating large
  imbalances in the carbon cycle
• The concentration of CO2 in the atmosphere is
  going up year by year

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Biogeochemical Cycles

• Water Cycle
• All life depends on the presence of water
• 60 of the adult human body weight is water
• Amount of water available determines the nature
  and abundance of organisms present
• It can be synthesized and broken down
• Synthesized during cellular respiration
• Broken down during photosynthesis

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Biogeochemical Cycles

• Basic water cycle
• Liquid water from the Earths surface evaporates
  into the atmosphere
• Occurs directly from the surfaces of oceans,
  lakes, and rivers
• Terrestrial ecosystems 90 of evaporation is
  through plants
• Water in the atmosphere is a gas
• Cools and falls to the surface as precipitation

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Biogeochemical Cycles

• Groundwater under ground water
• Aquifers permeable, underground layers of rock,
  sand, and gravel saturated with water
• Important reservoir 95 fresh water used in
  United States
• Two subparts
• Upper layers constitute the water table
• Lower layer can be tapped by wells

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Biogeochemical Cycles

• Water cycle

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Biogeochemical Cycles

• Changes in the supply of water to an ecosystem
  can radically alter the nature of the ecosystem
• Deforestation disrupts the local water cycle

• Water that falls as rain drains away

• Tropical rain forest ? semiarid desert

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Biogeochemical Cycles

• Nitrogen Cycle
• Nitrogen is a component of all proteins and
  nucleic acids
• Usually the element in shortest supply
• Atmosphere is 78 nitrogen
• Availability
• Most plants and animals can not use N2 (gas)
• Use instead NH3, and NO3-

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Biogeochemical Cycles

• Nitrogen fixation synthesis of nitrogen
  containing compounds from N2
• Nitrification N2 --gt NH3 --gt NO3-
• Denitrification NO3- --gt N2
• Both processes are carried out by microbes free
  or living on plant roots
• Nitrogenous wastes and fertilizer use radically
  alter the global nitrogen cycle
• Humans have doubled the rate of transfer of N2 in
  usable forms into soils and water

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Biogeochemical Cycles

• Nitrogen Cycle

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Biogeochemical Cycles

• Phosphorus cycle
• Phosphorus is required by all organisms
• Occurs in nucleic acids, membranes, ATP
• No significant gas form
• Exists as PO43- in ecosystems
• Plants and algae use free inorganic phosphorus,
  animals eat plants to obtain their phosphorus

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Biogeochemical Cycles

• Phosphorus cycle

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Biogeochemical Cycles

• Limiting nutrient weak link in an ecosystem
  shortest supply relative to the needs of
  organisms
• Iron is the limiting nutrient for algal
  populations
• Nitrogen and phosphorus can also be limiting
  nutrients for both terrestrial and aquatic
  ecosystems

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Flow of Energy in Ecosystems

• Energy exists as
• Light
• Chemical-bond energy
• Motion
• Heat
• First Law of Thermodynamics energy is neither
  created nor destroyed it changes forms

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Flow of Energy in Ecosystems

• Organisms do not convert lost heat to any of the
  other forms of energy
• Second Law of Thermodynamics whenever organisms
  use chemical-bond or light energy some is
  converted to heat (entropy)
• Earth functions as an open system for energy
• Sun our major source of energy

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Flow of Energy in Ecosystems

• Earths incoming and outgoing flows of radiant
  energy must be equal for global temperatures to
  stay constant
• Human activities are changing the composition of
  the atmosphere
• Greenhouse effect heat accumulating on Earth,
  causing global warming

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Flow of Energy in Ecosystems

• Trophic levels which level an organism feeds
  at
• Autotrophs self-feeders synthesize the
  organic compounds of their bodies from inorganic
  precursors
• Photoautotrophs light as energy source
• Chemoautotrophs energy from inorganic oxidation
  reactions
• prokaryotic

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Flow of Energy in Ecosystems

• Heterotrophs cannot synthesize organic
  compounds from inorganic precursors
• animals that eat plants and other animals
• fungi that use dead and decaying matter
  (detritivores)

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Flow of Energy in Ecosystems

• Trophic levels
• Primary producers autotrophs
• Consumers heterotrophs
• Herbivores first consumer level
• Primary carnivores eat herbivores
• Secondary carnivores eat primary carnivores or
  herbivores
• Detritivores eat decaying matter
• Decomposers microbes that break up dead matter

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• Trophic levels within an ecosystem

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Flow of Energy in Ecosystems

• Productivity the rate at which the organisms in
  the trophic level collectively synthesize new
  organic matter
• Primary productivity productivity of the
  primary producers
• Respiration rate at which primary producers
  break down organic compounds

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Flow of Energy in Ecosystems

• Gross primary productivity (GPP) raw rate at
  which primary producers synthesize new organic
  matter
• Net primary productivity (NPP) is the GPP less
  the respiration of the primary producers
• Secondary productivity productivity of a
  heterotroph trophic level

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Flow of Energy in Ecosystems

• Standing crop biomass chief static property of
  a population or trophic level the amount of
  organic matter present at a particular time
• Fraction of incoming solar radiant energy
  captured by producers is 1/year
• Used to make chemical-bond energy
• ATP for metabolic processes

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Flow of Energy in Ecosystems

• 50 of chemical-bond energy is not assimilated
  and is egested in feces
• 33 of ingested energy is used for cellular
  respiration
• 17 ingested energy is converted into insect
  biomass

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• Ecosystem productivity per year

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Flow of Energy in Ecosystems

• Limits on top carnivores exponential decline of
  chemical-bond energy limits the lengths of
  trophic chains and the numbers of top carnivores
  an ecosystem can support
• Little energy
• Large carnivores
• Longest chains occur in the oceans
• Top carnivore populations are small

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Flow of Energy in Ecosystems
Humans may not have metabolic access to all
calories in plants... Other organisms make fats
and metab. byproducts helpful to humans

• Flow of energy through the trophic levels of
  Cayuga Lake

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Flow of Energy in Ecosystems

• Trophic level interactions
• Trophic cascade process by which effects
  exerted at an upper level flow down to influence
  two or more lower levels
• Top-down effects when effects flow down
• Bottom-up effects when effect flows up through
  a trophic chain

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Flow of Energy in Ecosystems

• Top-down effects in a simple trophic cascade in a
  New Zealand stream

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Flow of Energy in Ecosystems
Top-down effects in a four-level trophic cascade.
Stream enclosures with and without large
carnivorous fish
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Flow of Energy in Ecosystems

• To predict bottom-up effects must take into
  account life history of the organisms
• When primary productivity is low, producer
  populations cannot support herbivore populations
• As primary productivity increases, herbivore
  populations increase
• Increased herbivore populations lead to carnivore
  populations increasing

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Flow of Energy in Ecosystems

• Bottom up effects