Ecosystem

• Introduction & Structure

  • Definition: Functional unit of nature, interaction of biotic and abiotic components.
  • Biotic Components
    • Producers (Autotrophs): Plants, algae.
    • Consumers (Heterotrophs): Herbivores, carnivores, omnivores.
    • Decomposers (Saprotrophs): Fungi, bacteria.
  • Abiotic Components
    • Climatic factors: Light, temperature, water, precipitation.
    • Edaphic factors: Soil, minerals, pH.

• Functional Aspects

  • Productivity
    • GPP (Gross Primary Productivity): Total rate of biomass production.
    • NPP (Net Primary Productivity): Available biomass for consumption ($GPP - R$).
    • Secondary Productivity: Rate of assimilation by consumers.
  • Decomposition
    • Definition: Breakdown of complex organic matter into inorganic substances.
    • Steps: Fragmentation, Leaching, Catabolism, Humification, Mineralization.
    • Factors: Temperature, soil moisture, chemical composition of detritus.
  • Energy Flow
    • Unidirectional flow.
    • 10% Law (Lindeman's Law): Only 10% energy transferred to the next trophic level.
    • Trophic Levels: Producers $\rightarrow$ Primary Consumers $\rightarrow$ Secondary Consumers $\rightarrow$ Tertiary Consumers.
  • Nutrient Cycling (Biogeochemical Cycles)
    • Gaseous Cycles: Carbon cycle, Nitrogen cycle.
    • Sedimentary Cycles: Phosphorus cycle, Sulphur cycle.

• Ecological Pyramids

  • Pyramid of Number
    • Upright (Grassland, Pond ecosystem).
    • Inverted (Parasitic food chain, Tree ecosystem).
  • Pyramid of Biomass
    • Upright (Terrestrial ecosystem).
    • Inverted (Aquatic ecosystem - phytoplankton to fish).
  • Pyramid of Energy
    • Always upright (energy is lost at each step).

• Ecological Succession

  • Definition: Gradual and predictable change in species composition in a given area.
  • Pioneer Species: First species to invade a bare area (e.g., lichens, phytoplankton).
  • Climax Community: Stable, final community in near equilibrium with environment.
  • Types
    • Primary Succession: Starts on bare rocks, cooling lava, newly formed sand.
    • Secondary Succession: Starts in abandoned farm lands, burned or cut forests.
  • Specific Successions
    • Hydrarch: Succession in water body (Hydric $\rightarrow$ Mesic).
    • Xerarch: Succession in dry areas (Xeric $\rightarrow$ Mesic).

• Ecosystem Services

  • Definition: Products of ecosystem processes.
  • Examples
    • Purifying air and water.
    • Mitigating droughts and floods.
    • Nutrient cycling.
    • Generating fertile soil.
    • Providing wildlife habitat, crop pollination, and aesthetic value.
  • Cost: Robert Costanza estimated global ecosystem services at US $33 trillion a year.