AEC 360    Ecology

Lecture 7:  How are ecological communities distributed?

I.  Definitions
    A.  Biome:  terrestrial biological communities grouped according to their dominant plant form (Fig. 6.3)

    B.  Biomes are determined by their plants
        1. plants have high surface area exposed to their environment and no means of controlling their internal environment
        2. plants have developed similar adaptations to deal with conditions in similar environments
        3. plants provide communities with their overall character
        4. plants are primary producers and provide basis of food web in terrestrial systems

     C. biome concept is a tool to understand and characterize the structure and function of large ecological systems
            - no distinct boundaries between biomes
            - history, random events, evolution, and species interactions will all affect what specific organisms are found in each local community

    D.  The primary determinants of the distribution of biomes are temperature and precipitation

       1.  Why deserts and rainforests occur where they do:  Hadley Cell (Fig. 5.6)


    D.  How to interpret climate diagrams (Fig. 6.4)
        1.  Recognizes importance of variation in climate throughout the year
        2.  Plots ecologically meaningful relationship between water and temperature
        3.  For every 10 degrees C in additional monthly temperature, 20 mm rainfall is needed for plant production
        4.  When line for precipitation is above line for temperature, plants can grow  (precipitation exceeds potential        
            evapotranspiration, 20 mm of rainfall for each 10 degrees C provides sufficient moisture for plant growth)

II.  Biomes of the world
    A.  Temperate Forest Biome (Fig. 6.8)
        - Deciduous trees
        - Moderate to high diversity
        - Fertile soils

    B.  Temperate Grassland Biome (Fig. 6.10)
        - Fertile soils
        - High diversity of non-grass plants
        - Fire important

         - Adaptation: Rhizomes

            grasses have rhizomes (underground stems) that allow them to rapidly grow back after fire events
            many plant species also have fire-resistant seeds 

    C.  Desert Biome (Fig. 6.13)
        - Soils infertile, fragile
        - Plants adapted to drought


    D.  Tundra Biome (Fig. 6.5)
        - Tree-less
        - Nutrient poor
        - Permafrost soils

         - Adaptation: Protective coat

            double-layered coats provide additional protection
            fur/feathers change from white in winter to brown in summer
            clear fur allows sunlight to heat skin
            fur/feather on feet prevent sinking in snow and lower heat loss 

    E.  ??????????????? (Fig. 6.11)

        Adaptation Epiphytes
            epiphytes grow on branches of other trees,  adaptation gives greater access to light

F.  Tropical seasonal forest/savanna (Fig. 6.12)

        -continuous high temperature but seasonal variation in precipitation with distinct dry period
        -seasonal forest: deciduous trees
        -savanna: grassland with scattered trees

        - Adaptation Migration

            wildebeest make use of regional variation in rainfall - move from southern region in rainy season to northern region in dry season