Chapter 55

Chapter 55: Ecosystems and Restoration Ecology

Concept 55.1: Physical Laws Govern Energy Flow and Chemical Cycling in Ecosystems

• Energy Flow vs. Chemical Cycling:

  • Energy flows through an ecosystem in a one-way direction.

  • Chemicals cycle within the ecosystem.

• Energy Flow:

  • Light energy from the sun is converted to chemical energy by plants.

  • Organisms use this chemical energy to perform work. Heat is released as a byproduct.

• Chemical Cycling:

  • Plants take up chemicals from the soil.

  • These chemicals are passed to organisms that consume the plants.

  • Decomposers break down dead organisms and return chemicals to the soil, completing the cycle.

• Conservation of Energy: Energy cannot be created or destroyed, only transferred or changed.

• Conservation of Mass: Mass cannot be created or destroyed, only transferred or changed.

Concept 55.2: Energy and Other Limiting Factors Control Primary Production in Ecosystems

• Primary Production Defined: The amount of light energy converted to chemical energy by autotrophs (primarily plants) during a given period.

• Ecosystem Energy Budgets:

  • An ecosystem's energy budget depends on primary production.

• The Global Energy Budget:

  • The amount of solar radiation reaching Earth limits photosynthetic output of ecosystems.

• Gross and Net Production:

  • Gross Primary Production (GPP): Total primary production in an ecosystem.

  • Net Primary Production (NPP): GPP minus the energy used by primary producers for respiration (R).

    • NPP = GPP - R

  • NPP represents the storage of chemical energy available to consumers in the ecosystem.

• Primary Production in Aquatic Ecosystems:

  • Light Limitation: Light intensity affects primary production in aquatic ecosystems.

  • Nutrient Limitation: Nutrient availability limits primary production.

• Primary Production in Terrestrial Ecosystems:

  • Nutrient Limitations: Soil nutrients often limit primary production.

  • Climate Change: Variations in temperature and moisture affect primary production.

Concept 55.3: Energy Transfer Between Trophic Levels Is Typically Only 10% Efficient

• Secondary Production: The amount of chemical energy in food converted to new biomass during a given period of time.

• Production Efficiency:

  • The fraction of energy stored in food that is not used for respiration.

  • Production \ Efficiency = (Net \ Secondary \ Production \times 100) / Assimilation \ of \ Primary \ Production

• Trophic Efficiency and Ecological Pyramids:

  • Trophic efficiency is the percentage of production transferred from one trophic level to the next (usually around 10%).

  • Energy is lost at each transfer, primarily due to respiration and incomplete consumption.

  • Ecological Pyramids: Illustrate the relative energy or biomass at each trophic level.

    • Pyramid of Energy: Shows the flow of energy through trophic levels.

    • Pyramid of Biomass: Shows the dry weight of all organisms at each trophic level.

    • In some aquatic ecosystems, the biomass pyramid may be inverted, with primary consumers having more biomass than primary producers (occurs where phytoplankton reproduce and are consumed rapidly).

Concept 55.4: Biological and Geochemical Processes Cycle Nutrients and Water in Ecosystems

• Decomposition and Nutrient Cycling Rates:

  • Decomposition rates affect nutrient cycling.

  • Decomposition is faster in warmer ecosystems.

• Biogeochemical Cycles:

  • Water Cycle:

    • Driven by evaporation, transpiration, precipitation.

    • Water moves between the ocean, atmosphere, and land.

  • Carbon Cycle:

    • CO2 is taken up by plants through photosynthesis and released through cellular respiration.

    • Burning of fossil fuels and wood releases CO2 into the atmosphere.

  • Nitrogen Cycle:

    • Nitrogen fixation converts N2 to forms that can be used by plants.

    • Nitrification converts ammonium to nitrate.

    • Denitrification converts nitrate back to N2.

  • Phosphorus Cycle:

    • Weathering of rocks releases phosphate into the soil.

    • Phosphate is taken up by plants and passed to consumers.

    • Decomposition returns phosphate to the soil.

Concept 55.5: Restoration Ecologists Return Degraded Ecosystems to a More Natural State

• Bioremediation: Using organisms to detoxify polluted ecosystems.

• Biological Augmentation: Using organisms to add essential materials to ecosystems.