BIO 360  Ecology

Lecture 37: Ecosystems -- production and decomposition

I.  What is an ecosystem?
    A.  a biological community plus all of the abiotic factors influencing that community

    B.  Elton (1920's) -- feeding relationships link organisms into a single biological entity

    C.  Lindeman (1940's) -- the trophic dynamic concept

        1.  Energy flows through food chains in a trophic pyramid, which is regulated by laws of thermodynamics

        2.  First, energy is neither created or destroyed
            Implication: can perform an energetic accounting for an ecosystem

        3.  Second, transformations of energy are inefficient
            Implication: accounts for energy losses, which may take the form of waste

        4.  Ecological efficiency is the percentage of energy transferred from one trophic level to the next

II.  Production

    A.  Primary production is the fixation of energy by autotrophs (mainly plants and algae) in an ecosystem
        1.  Controls the dynamics of the rest of the food chain


        2.  Humans use ~40% of primary production

    B.  How ecologists measure primary production

    C.  What controls primary production?






III.  Decomposition is the breakdown of organic matter

    A.  Critical to nutrient regeneration

    B.  A key ecosystem process

    C.  Decomposition happens in four ways

        -Water leaching out soluble material
        -Consumption by large detritivores
        -Breakdown of wood and leaves by fungi
        -Bacterial consumption of almost everything

    D.  Relationship between decomposition, nutrient uptake and community of microorganisms

    E.  Rate of decomposition influenced by



    F.  Differences in nutrient regeneration on land and in water

       1.  On land, regeneration on land takes place close to plant roots
            - Photic zone often far removed from sediments

        2. Terrestrial decomposition is mostly aerobic

    E.  Nutrient regeneration and loss
        1.  Nutrients are regenerated in ecosystems through weathering, decomposition, and biological accumulation


        2.  Nutrients are lost from ecosystems during disturbance