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FRESHWATER BIOLOGY (Biol 207)

Fall 1996

MidTerm Exam - 100 pts

Name:

Definitions (2 pts each)

1) aquatic nursery area -

2) profundal zone -

3) phytoplankton bloom -

4) suspension-feeder -

5) detritus -

Short Answer (4 pts each)

1) Why is water potentially dangerous to freshwater organisms?

2) How can tiny planktonic bacteria -- only 0.001 mm big -- be so important in FW systems?

3) Give a physical/structural reason why macrophytes are so important to epifauna.

4) Give 2 reasons why is there no plankton in air?

5) Why can you never step in the same stream twice?

Longer Answer (but not too long)

2) You collect and compare an entire, intact water lily plant to a terrestrial plant with similar dimensions and the same size. Both plants are dried out (i.e., no water is left on/in plants) before you conduct lab analyses. (12 pts)

a) why does it take the lily less time to dry out completely?

b) which plant weighs less and why?

c) which plant has more rigid material in its structure and why?

d) which plant has more photosynthetic pigment per cell and why?

3) You have studied a lake ecosystem for 15 years and thus are familiar with all the organisms and their interactions. One year someone inadvertently releases a spiny water flea (an exotic zooplankter with huge spines that repel fish) into the lake. What are your predictions for the effects of this introduction on the following organism populations 5 years from now. Explain each prediction. (15 pts)

a) native zooplankton

b) native phytoplankton

c) native fish (most of which eat zooplankton as juveniles)

d) submerged macrophytes

e) native clam populations (herbivorous suspension-feeders)

4) You are biologist that studies the stream we visited this week. In the fall you notice that DO levels drop, as does water temperature. In the spring, you find the opposite pattern. You also observe that many stream insects in the spring spend most of their time scraping the tops of rocks. By contrast, in the fall, these insects split their time between foraging periods under and between rocks, and periods on the tops of rocks where they flap their external gills. (During these spring & fall observation periods you find very similar current speeds, water depths, and temperature regimes - though the temperature changes are going in opposite directions.) (16 pts)

a) how can you explain the DO/temp patterns in spring & fall?

b) how can you explain the insect behaviors in spring & fall and are they related to (a)?

5) A scientific study reports that emergent plants in a wetland benefit benthic, detritivorous insect larvae in the middle of a river. (15 pts)

(a) How can this be?

(b) To boost the numbers of these larvae (which are important fish food), a person proposes to cut down cattails and dump them onto the river bottom. How might this affect the larval populations?