PCB 4301 Your Name:_________________________
Freshwater Ecology
Fall, 1999
Hour Exam
Instructions: Choose 8 of the following 10 questions to answer. You will take the other 2 questions home and can answer them as open-book questions, turning in the answers on Thursday.
Fill in the following blank:
The questions I will use as open-book questions are:_______________
1. Many of water's interesting physical properties are due to the polar nature of water molecules. List these properties, and describe the important benefits and or challenges that these properties present to aquatic organisms.
2. The Reynolds number describes the ratio of what types of forces in flowing water? If Re is small, what types of forces prevail? What is the importance of Re to aquatic organisms? Calculate Re for a rotifer (diameter = 60 microns) swimming at 0.5 m h-1 and a small shrimp, 1 cm long swimming at 0.15 m s-1. Which organism is likely to be most constrained by the rate of diffusion of gases in water?
3. Explain (using appropriate chemical equations) how the metabolism of organisms leads to the precipitation and dissolution of limestone.
4. The diffuse attenuation coefficient measured during summer in a deep south Florida lake was 0.3 m-2. Roughly how deep is the compensation depth for phytoplankton? How deep would you predict that you would find rooted benthic aquatic plants? What other aspects of the lake's environment may influence these depths?
5. After a long, windless week on lake Wobegon, a freshwater ecology class measures the vertical distribution of chlorophyll in the water column. They find that there is a large peak in the chlorophyll concentration at a depth of 6 meters. In the absence of any further information, explain this distribution, and correctly use the terms epilimnion, metalimnion and hypolimnion in your answer.
6. You hypothesize that the population density of rotifers in south Florida lakes is controlled by predatory copepods. Describe the field and lab data or experiments you would use to test this hypothesis, including why this data or experiment is necessary. What do you need to know about the distribution of rotifers and copepods in order to adequately design your sampling?
7. What is the difference between gross efficiency of production and net efficiency? When would you use one vs. the other to describe efficiency and why?
8. When the log of respiration rate is plotted against the log of body weight for various aquatic organisms at 20 oC, the plot forms a line whose slope is 0.794. For a cladoceran that weighs 0.5 mg dry weight, the respiration rate is 0.044 µl O2 h -1. What is the equation for the relationship of respiration to body weight in this case?
9. You find that a population of green algae in your lab has 50 individuals ml-1. Two days later there are 200 individuals ml-1.
a. What is the population growth rate for this algae?
You take the same from you culture and put it in the OE pond, at an initial concentration of 50 individuals ml-1 and find in 2 days that there are 100 ind ml-1.
b. What is the population growth rate in this second case? What are the possible reasons for the difference between these two growth rates?
10. You sample a cladoceran population in the Everglades and find 100 females. Each female carries 19 eggs. The time required for development of the eggs is 5 days. What is the birth rate in this population? You resample after 10 days and find 250 females. What is the growth rate and the death rate for this population?