BIO 402: Field Biology

BIOGEOGRAPHY AND THE ENVIRONMENT

BASIC QUESTION: Why do species have the distribution we see?

              In theory every species could live on all parts of the planet.  But they don’t.  Why?

              See first graphic: Methods of explaining distributions

REASON #1:  DISPERSAL PROBLEMS

Species are unable to travel to all locations.  Once a barrier is broken, they can distribute further.

Examples:

1. Starlings originally were limited to Europe and Asia, could not cross Atlantic Ocean
   * they were introduced to New York City in 1890s by humans
   * now distributed throughout North America
   
2. Colorado Potato Beetle originally in Colorado and Texas
   * fed and lived on wild sand-bur
   * with introduction of potato, beetle added this plant to it’s diet
   
3. Chestnut blight once limited to China on the Chinese Chestnut
   * the fungus was introduced to New York around 1900 with introduced Chinese trees
   * fungus has infected and hilled above ground portion of American Chestnut trees
   * fungus now known where American Chestnut once grew in abundance

REASON #2:  BEHAVIORAL PATTERNS

Activities of species limit ability to move and/or reproduce.

Example:

The mosquito Anopheles culicifacies has a hovering dance 1-2 cm above water
* cannot complete the dance with dense vegetation
* hence species missing from ponds and marshes with dense vegetation

REASON #3:  INTERACTIONS WITH OTHER SPECIES

Competition, predation and parasitism can limit distribution.

Examples:

1. Lake Trout and Sea Lamprey in coastal Canadian waters and into Great Lakes.
   * lamprey parasitic on trout; hence trout not found in coastal waters of Siberia
   * trout numbers reduced in Great Lakes due to introduction of lamprey
   
2. Black Walnut produced toxin that inhibits crop growth (known as allelopathy)
   * tomato and alfalfa do poorly in fields adjacent to walnut trees
   * this pattern common among species in arid regions with competition for water
   
3. Species of Gammarus (an amphipod) in England compete with each other.
   * Gammarus pulex is freshwater only
   * Gammarus dueberi usually common in brackish and freshwater habitats
   * G. dueberi is unable to survive at locals with G. pulex present

REASON #4: ENVIRONMENTAL CONDITIONS

Physical and chemical factors of the environment define a species’ ability to live.

Environmental survival fits into one of three groups:

In Zone of Optimum one will see the highest population numbers
    * ideal habitat for survival and reproduction

In the Zone of Physiological Stress populations are more scattered and/or smaller
    * habitat is not ideal, hence reduced survival and/or reproduction

The habitat is unsuitable for life in the Zone of Intolerance

Examples:

1. Wild madder is limited by winter temperatures
   * distribution in Europe south of the 4.5oC January isotherm
   
2. Loblolly Pine (Pinus taeda) distribution limited by several combined factors:
   * northern range limited by winter temperatures
   * southern distribution limited by a combination of:
   - monthly average temperatures
   - number of days with rainfall & average monthly precipitation
   - length of frost-free season
   * transplants show genetic difference in susceptibility
   
3. Fire important in seed release and dispersal of Lodgepole pine
   * several subspecies with distinct distributions
   * all subspecies must have open areas to germinate and for seedling growth
   * have different heat requirements for cones to open; some forms require fire (serotinous)
   
4. Many species of coastal California limited by moisture
   * some need high moisture, other do best with dryer climate
   * some species look different with changes in moisture conditions
   * for some, it’s a combination of temperature and precipitation that limits distribution
   
5. Light intensity is critical to some plant species in forests
   * seedlings need optimum light for growth
   * oaks and beech need lower light intensity
   * pines need higher light intensity
   
6. Soil pH limits the distribution of numerous species
   * red cedar restricted to circumneutral soils (around pH 7)
   * Sphagnum produced acids and thrives in acid water (pH<7)
   * snails and clams have shells with calcium that dissolve in acid waters
   
7. Pollution can modify the environment of organisms
   * coal burning has caused trees to be darker with soot in England
   * Peppered moth color patterns have changes (light à dark)