Autumn.wmf (12088 bytes) Concepts of Biology (BIOL116) - Dr. S.G. Saupe; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321;;

Ecology:  Biosphere & Biomes

I.  Definitions/Introduction.

II.  Interactions.  the biotic and abiotic components of the biosphere interact with one another.  Interaction is the name of the game. 

A.  Organisms interact with one another.  
    These interactions can be positive (i.e., plants and pollinators; ants and acacias) or negative (i.e., predation, competition, disease),  We discussed this, among other places, in our Community lecture.

B.  Organisms interact with their environment.  

  1. Organisms are affected by various abiotic factors such as: (a) water availability; (b) salinity; (c) nutrient availability; (d) light (quality and quantity); (e) oxygen (aerobic/anaerobic); (f) elevation; (g) soil type; (h) wastes; (i) temperature; and (j) countless others.

  1. Organisms affect their environment.  For example, vegetation plays a role in water recycling and recall that plants absorb carbon dioxide and release oxygen.  Consider the Gaia Hypothesis and the explanation for why the temperature of the earth has remained relatively stable even though solar output has increased.  How can this be?  Plants and other critters have essentially regulated the degree of insulation (carbon dioxide surrounding earth).

III.  Biosphere is comprised of diverse assemblages (biomes) of species.  
Wallace divided the biosphere in to biogeographic realms (Nearctic � North America; Palearctic � Europe; N. Asia, Australia; Ethiopian � African, Oriental � SE Asia; Neotropical  - Central and South America).  Within these realms, major ecosystem types, or biomes, predominate.

The major terrestrial biomes include:  (1) desert; (2) grassland (prairie, veldt, steppe, savanna); (3) tropical forests; (4) temperate deciduous forest; (5) evergreen coniferous forests (also called boreal forest or taiga); (6) tundra (arctic and alpine). Note that there are many subdivisions of these that we will not discuss.

A.  General.
For each terrestrial biome, know: (1) location; (2) general climate, (3) general appearance, and (4) characteristic species (plants and animals).

B.  There is no sharp boundary between biomes, they grade into one another.

C.  Biome type is ultimately determined by:

  1. Soil type and bed rock.
        Note -
    soil is a mixture of organic materials such as partially decayed animals and plants, fecal matter (humus); inorganic materials such as minerals in various particle sizes; gases such as oxygen and carbon dioxide; and liquid (like water).

  1. Climate.
        The prevailing weather conditions are determined by factors such as temperature, humidity, wind, precipitation, cloud cover. 

  1. Climograph (graph of mean annual temperature vs. precipitation).  
        Terrestrial biome distribution is largely influenced by temperature and precipitation.  If we plot the distribution of biomes on a climograph (plot of mean annual temperature vs. mean annual precipitation) it is appararent that they sort out nicely.

  1. There are several factors that influence climate: 

  • Solar radiation.  
        Because the earth is a sphere and at an angle relative to the sun, there is unequal heating of the earth's surface.  Hotter at equator than poles. 

  • Rotation of the earth.
        This is responsible for air currents (belts of easterlies and westerlies), rainfall patterns at different latitudes (i.e., dry at 30 degrees N and S; moist at 60 degrees), seasonal variations, and ocean currents.

  • Distribution of continental land masses and oceans 
    These are important in the rainshadow effect, ameliorate temperature

  • Elevation (latitude).

  1. Presence of periodic disturbances (e.g., fire)

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Last updated: May 10, 2004        � Copyright by SG Saupe