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Environmental Science: A Global Concern, 7/e

William P. Cunningham, University of Minnesota
Mary Ann Cunningham, Vassar College
Barbara Woodworth Saigo, St. Cloud State University

Population Dynamics

Essay Quiz


1		The best way to appreciate the explosive power of exponential growth is to follow the arithmetic for yourself. Get a calculator! A typical sheet of paper is approximately 0.1 mm thick. Take a sheet of paper and fold it in half. You have now doubled the thickness to 0.2 mm. Fold it again, doubling its thickness to 0.4 mm. Keep folding. It gets hard to do this more than five times, at which point your wad of paper is 3.2 mm thick. Now, using a calculator to keep track of the thickness of the wad, continue to fold the paper in your mind. The question is this: How many times must the paper be folded in half before its thickness exceeds the height of Mt. Everest? Everest is 8,850 meters tall. (Remember, a meter contains 1,000 mm.)



2		Define biotic potential.



3		Describe the relationship between environmental resistance and carrying capacity.



4		Contrast the characteristics of species employing Malthusian growth strategies with those using logistic strategies.



5		Explain the difference between how density-dependent and density-independent factors work to control population growth.



6		Evaluate this statement: The reason modern life expectancies are so much longer than they were generations ago is that human life spans have increased.



7		Can you think of an example of any material that can grow exponentially indefinitely in a finite space?



8		Earlier this century, large numbers of American elms were planted as boulevard trees in many U.S. cities. Most of these trees died in the devastating Dutch elm disease epidemic. a. Would you classify this disease as a density-dependent or density-independent force? b. What lesson is there for future plantings to make it less likely that such a costly and tragic event could ever happen again?



9		Early settlers on the Great Plains had their crops periodically destroyed by clouds of locusts that descended on their fields. Then the locusts would disappear for years before returning again in crushing numbers. These pests exhibited the classic overshoot and dieback pattern of the Malthusian growth strategy.Intuitively, it may seem that such explosive growth, stripping the land of edible plant matter, and the subsequent catastrophic dieback is not a beneficial strategy for these insects to follow. Make the counter argument. What possible advantages are there for a locust species that follows this strategy?



10		Human life expectancy in the coal regions of England in the early days of the Industrial Revolution reportedly was 17 years. In such a population, would you expect to find any 60- or 70-year-old people? Explain.



11		Visit the Current Global Environmental Issues map on this Web site. Under Wildlife, select the piece Snow goose population threatens arctic tundra. Also link to Images of degradation. Carrying capacity acts to limit population size. Can population growth reduce carrying capacity? Explain.

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