Ecosystems and Restoration Ecology: Chapter 55

  • An ecosystemconsists of all organisms living in a community and the abiotic factors with which they interact.
    • Range from microcosm's (aquariums) to large areas like lakes
  • external image 54-01-EcosystemDynamics-AL.gifAll ecosystems dynamics involve
    • Energy flow (through ecosystems)
    • Chemical cycling (cycles within ecosystem)
  • Physical laws govern energy flow and chemical cycling
    • Conservation of Energy
      • First law of thermodynamics: energy cannot be created or destroyed, only transformed.
        • Energy enters ecosystem as solar radiation, is conserved, leaves organisms as heat, is transferred to chemical energy by plants.
      • Second law of thermodynamics: every exchange of energy increases the entropy of the universe.
        • Energy conversion is not completely efficient, some is always lost as heat.
    • Conservation of Mass
      • Law of conservation of mass: matter cannot be created or destroyed
        • Chemical elements are recycled
    • Ecosystems are open systems that absorb mass and energy and release heat and waste products.
    • Energy, Mass, and Trophic Levels
      • Autotrophs: create their own food.
        • Primary producers: use photosynthesis or chemosynthesis to build their own molecules to use as an energy source.
      • Heterotrophs: depend on the output of primary producers.
        • Primary consumers: herbivores, consume primary produces
        • Secondary consumers: carnivores that eat herbivores
        • Tertiary consumers: carnivores that eat carnivores.
      • Detritivores (decomposers): consumers that derive their energy from detritus,nonliving organic matter.
        • Prokaryotes and fungi
        • Decomposition connects to all trophic levels
  • Primary productionis the amount of light energy converted to chemical energy by autotrophs during a given time period.
    • An ecosystems energy budget is set by the extent of photosynthetic production.
    • The global energy budget is limited by the amount of solar radiation that reaches Earth's surface.external image NASA-NPP.jpg
      • Only a small fraction of solar energy is of a usable wavelength for photosynthesis.
    • Gross primary production (GPP)is the total primary production of the ecosystem.
      • Measure of the conversion of chemical energy from photosynthesis per unit time
    • Net primary production (NPP)is GPP minus the energy primary producers use for respiration
      • On average its about half the GPP
      • Only NPP is available to consumers
      • Greatly varies in different ecosystems
      • All ecosystems NPP contributes to the total NPP on Earth
    • Tropical rain forests, estuaries, and coral reefs are most productive ecosystems per unit area
    • Marine ecosystems are unproductive per unit area, but since they are such a great volume they contribute to the global NPP a lot.
    • Net ecosystem production (NEP)is a measure of the total biomass accumulation during a given time period.
      • GPP - total respiration of all organisms in an ecosystem
      • Estimated by comparing the flux of carbon dioxide and oxygen in an ecosystem.
    • In Aquatic Ecosystems
      • Primary production is controlled by light and nutrients
        • Light limitation: depth of light affects primary production in the photic zone
        • Nutrient limitation: a limiting nutrientis the element that must be added for production to increase in an area.
          • Nitrogen and phosphorus are most limited
        • Adding nutrients to lakes has ecological impacts. Sewage run off can cause eutrophication which can cause many fish to die. Phosphorus also limits cyanobacterial growth, so phosphate-free detergents have become more common.
    • In Terrestrial Ecosystems
      • Primary production is affected by temperature and moisture.
        • Production increases with moisture.
        • Actual evapotranspiration: total amount of water transpired by plants and evaporated from a landscape. It is affected by precipitation, temperature, and solar energy. It is related to net primary production.
      • Soil nutrient is often the limiting factor
        • Nitrogen is most common limiting agent, phosphorus is also (primarily in older soil).
        • Adaptations help plants access limited nutrients:
          1. Mutualism with nitrogen-fixing bacteria
          2. Mycorrhizal fungi
          3. Root hairs to increase surface area
          4. Enzymes that increase the availability of limiting nutrients.
  • Energy transfer between trophic levels is only 10% efficient
    • Secondary production is the amount of chemical energy in food converted to new biomass during a given period of time.
    • Production efficiency= (Net secondary production X 100%)/(Assimilation of primary production)
      • Birds and mammals efficiency = 1-3%
      • Fishes = 10%
      • Insects and microorganisms = <40%
    • Trophic efficiencyis the percent of production transferred from one level to the next.
      • Range from 5-20%
      • Multiplies over the food chain's length
      • About 0.1% of energy from photosynthesis reaches a tertiary consumer
      • A pyramid of net production represents the loss of energy with each transfer in a food chain.
      • A biomass pyramid shows the dry weight of all organisms in one trophic level.
        • Usually a decrease at higher trophic levels
        • Turnover time is a ratio of the standing crop biomass to production.
  • Biogeochemical cycles:nutrient circuits in ecosystems that involve biotic and abiotic components.
    • All elements cycle between organic and inorganic reservoirs.

Water cycle

external image Water_cycle.png

Carbon cycle

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Nitrogen Cycle

external image 54_17NitrogenCycle_L.jpg

Phosphorus Cycle

external image 55_14dPhosphorusCycle-L.jpg

  • Decomposition and Nutrient Cycling Rates
    • Decomposers play a key role in chemical cycling since rates at which nutrients cycle vary with rates of decomposition.
    • Rate of decomposition is controlled by temperature, moisture, and nutrient availability.
    • Rapid decomposition = low levels of nutrients in the soil

Restoration Ecology

  • Returns degraded ecosystems to a more natural state.
    • Over time biological communities can recover from disturbances.
  • Restoration ecologists try to initiate or speed up recovery.
  • Bioremediationis using living organisms to detoxify ecosystems
    • Often uses prokaryotes, fungi, or plants that can take up and sometimes metabolize toxins.
  • Biological Augmentation uses organisms to add essential materials to a degraded ecosystem.

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