COMMUNITY ECOLOGY

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Community: any collection of organisms in a given area

  • Community Structure
      species list
      diversity
      importance/dominance
        biomass
        productivity
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    • Community Structure

  • Keystone Species: structure reorganized if keystone species removed
    (Robert Paine, 1969)
    vs. dominants



    Example: sea otters > sea urchins > kelp (Monterey Bay)




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    • PLANT COMMUNITIES

    • Individualistic approach
    • Typal approach
    Whittaker, R.H. 1967. Gradient analysis of vegetation. Biological Riview 42: 207-264.
    Yeaton, R.I. 1981. Seedling morphology and the altitudinal distribution of pines in the Sierra Nevada of central California: a hypothesis. Madroņo 28:65-77.
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    PLANT COMMUNITIES

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    CHANGES IN COMMUNITY STRUCTURE

    • Succession: sequence of species following disturbance
      (ecological time scale years - decades)
      • Primary Succession: colonization of bare rock, rockslides, exposed ocean floor, glacier retreat
      • Secondary Succession: occupation of abandoned fields, roads, and villages [.]
        • Early Successional Species: "weeds" poor soils, low water, sunny, drought
        • Mid-Successional Species: light-tolerant trees and shrubs
        • Late Successional ("Climax") Species: shade tolerant, competitive
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    CHANGES IN COMMUNITY STRUCTURE





    Community Function
    • productivity
    • nutrient cycling & energy
      size-distribution
      m = cM0.75
        m - Basal metabolic rate (cal/hr)
        M - biomass

        0.75 = "Kleiber's Law"
              (vs. 0.67)



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    Community Structure

  • Large animals better able to survive droughts and famines, because the energy storage capacity increases linearly with mass.

  • Small animals maintain higher populations, because they need fewer resources (lower probability of extinction)

  • Terrestrial communities always contain more species of small-bodied animals than large-bodied ones (structure!).






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    • Community Structure
  • Large animals have large ranges
  • Some small animals have large ranges -
      particularly small carnivores next




    • COMMUNITY ECOLOGY

    Ecosystem: the interacting organisms in an area and their inclusive environment
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    ECOSYSTEM FUNCTION

  • Food (energy) transfer within communities
  • Food Webs
        (life stage, omnivores)

  • Trophic levels - Pyramids
    • fewer species for successive trophic levels
    • energy "10% rule" for successive trophic levels
    • biomass >10% or <10%
      • Productivity (flux) vs.
      • Biomass (standing crop)
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    • Biomass vs. Productivity

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    ECOSYSTEM FUNCTION

  • Aquatic Community Trophic Types
    • Eutrophic: high productivity
    • Oligotrophic: low productivity
    • Marine Near-shore Ecosystems
      • Estuaries, Salt Marshes, Mangrove Swamps
      • High biomass, high productivity
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