BOTANY 160       

MID-SEMESTER EXAM KEY                                           FALL 1993

I. Definitions: (Choose 5; 4pts each)

    Ombrotrophic bog - a type of peatland, dominated by Sphagnum moss 
      that is raised above the water table and which therefore receives 
      all its water from precipitation. This type of acid bog is 
      extremely nutrient poor.

    Compensation point - the intensity of radiation at which photosynthesis 
      equals and balances respiration.

    Reynolds number - a number summarizing the relative importance of 
      inertial to viscous forces in moving water. The magnitude indicates 
      whether the water motion is laminar or turbulent.

    Littoral zone - the area of a lake or pond that extends from the 
      shoreline out to the depth at which rooted aquatic plants can no 
      longer grow due to insufficient light.

    Collective properties - properties of a community that are a 
      composite of the lower levels of organization (individuals and 
      populations). (Examples: species diversity, community biomass and 
      productivity) [see your text - page 613]


II Short Answer:

  1. Describe and contrast the two types of ecosystem stability discussed 
     in class:


       Resilience - the rate with which a community (or ecosystem) returns 
         to its former state after it has been disturbed.

       Resistance - the ability of a community (or ecosystem) to avoid 
         displacement from its present state by a disturbance.

  2. Illustrate and label the temperature- and oxygen-depth profiles that 
     would be observed during the four seasons in a termperate-zone 
     eutrophic lake. (_No_credit_will_be_given_for_a_written_explanation_)

  3. What is meant by the River Continuum Concept 


       Energy sources supporting the biological community change in a 
       downstream direction. This concept extended and gave a functional 
       interpretation to classical river zonation work which was primarily 
       descriptive. [Key concepts: connection between the lower and upper   
       reaches and downstream organisms capitalize on inefficiency of 
       upstream  organisms]


  4. Describe and contrast the energy flow patterns in  a typical lake and 
     stream located in the Northeastern Deciduous Biome (Labelled diagrams 
     comparable to those in your text are acceptable)

       Grazers are very important to the energy flow in lake
       - systems. However, they contribute much less to the total energy 
       flow in a stream located in the northeastern deciduous forest where 
       allochthonous input and detritivores are the major factors in energy 
       flow. [see your text pages 679-680]


III Essay:



1. Recall that several weeks ago two scientists (an auecologist and a 
   synecolgist) were arguing about how to aquire a scientific ungderstanding 
   of the Shelburne Pond - Muddy Brook ecosystem. While paddling down Muddy 
   Brook they noticed an area of abundant sunshine where the rocks on the 
   stream bottom were a mosaic of living colors representing green, 
   blue-green and and brown diatom algae. They noted that the diatoms were 
   mostly on the tops of the rocks, the blue-greens on the sides and the 
   greens on the down-stream surfaces. the autecologist decided to apply 
   strong inference in attempting to understand why this pattern exists.

     a) Drawing on your knowledge from lecture and your readings list the 
        steps one follows in applying the strong inference method.

          Step 1 - Devise multiple hypotheses to explain the observed 
                   phenonema.
 
          Step 2 - Design and conduct an experiment to exclude (disprove) as 
                   many of the hypotheses as possible.

          Step 3 - Recycle back to step 1 to test remaining hypotheses or 
                   sequential hypotheses.

     b) Think of some multiple hypotheses to explain the observed pattern. 
        List them and briefly describe an experiment to test them.

           Any reasonable set of multiple hypotheses and appropriate 
           experimental design was acceptable.