Principles of Ecology


10 December 1997




(two or three phrases or sentences)

6 points each for a total of 72 points

1. Explain what a rain shadow is, and give an example of one.





2. Explain the difference between Liebig’s "law of the minimum," Shelford’s "environmental tolerance," and Grinnell’s concept of the ecological niche.





3. Define oscillating selection, and give 3 necessary conditions that would help to demonstrate the occurrence of oscillating selection.





4. Define what a population is, and give 3 characteristics of populations.





5. Predict the distribution of fast food restaurants in Alabama, and name an ecological process that could produce the distribution of fast food restaurants.





6. List 4 possible interactions between 2 species, and give an example for 2 of them.





7. Explain the difference between the competitive exclusion principle and the principle of limiting similarity.





8. Explain the difference between exploitation competition and interference competition.





9. For "nature’s 10-year cycle," list 3 possible explanations for why hares don’t go extinct when lynx are abundant and/or why lynx don’t go extinct when hares are scarce.





10. Explain the difference between the functional response and numerical response of a predator species.





11. List 3 ways in which competing species might reduce their overlap in resource use.





12. Define trophic level, food web, and keystone predation.






16 points each for a total of 64 points

13. Male yellow-headed blackbirds are either monogamous or bigamous, and follow the "Polygyny Threshold Model."


On the above pair of axes, draw fitness curves for 1st and 2nd mated female blackbirds. Label the 2 curves & 1 and & 2, respectively. For your curves, draw and label the polygyny threshold.

List 3 assumptions of the polygyny threshold model.





Predict the change in the polygyny threshold if the & 1 and & 2 curves were farther apart.





Describe how the frequency of bigamy should change from what you drew above, if the fitness of 1st mated females and 2nd mated females were equal within each territory.

PART II (continued).

14. Complete this cohort life table for North American pikas




[instruction: round your work off to 2 decimal places]









































































Give the formula for and calculate the value of the net reproductive rate (R0) and the length of one generation (G).





Will the population increase or decrease over time? Give the formula for the per capita intrinsic rate of natural increase (r). Is this r greater than, less than, or equal to zero?





Suppose a mutant individual produced 2 offspring at age 1 and then died. Give R0, G, and r for the mutant. Explain whether the mutant genotype would spread through the population.





15. In the eastern foothills of the northern Rocky Mountains, Columbian ground squirrels and another species, Richardson’s ground squirrels, compete for the same forage: meadow grasses. Suppose that these 2 species follow the Lotka-Volterra model of competition, with the following model parameters: K1 = 75, a = 0.75, K2 = 100, b = 1.00.

Mark and label the 4 intercepts of the 2 species zero-growth isoclines and draw and label the isoclines for each species on the graph axes below.



On the above graph, draw the trajectory of the populations if the starting densities are N1 = 75 and N2 = 10. What is the equilibrium outcome of the competition from this starting point?


On the above graph, draw the trajectory of the populations if the starting densities are N1 = 10 and N2 = 75. What is the equilibrium outcome of the competition from this starting point?


Columbian ground squirrels are larger in body size than Richardson’s ground squirrels. Explain whether this observation is consistent with your conclusions above.



16. Assume that lynx and hare populations have dynamics that are just like the Lotka-Volterra model for a predator and prey species. On the axes below, draw and label the zero-growth isoclines and their intercepts for populations of lynx (predator) and snowshoe hare (prey) in the North American arctic, if you know that the following conditions apply:

r1 = 0.40/hare; p1 = 0.02/hare•lynx

p2 = 0.002/hare•lynx; d2 = 0.300/lynx



Give the Lotka-Volterra equations for the rates of change in the prey and predator populations.




On the graph above, draw vectors for the changes in hare and lynx populations if you started at 2 different points:

1) N1 = 250, N2 = 10; and 2) N1 = 250, N2 = 40.

What would happen to the predator isocline if lynx became more efficient at producing lynx kittens from hares? What would the new lynx-hare cycle look like? (HINT: you can draw the isocline and new cycle in with dashed lines on the above graph).





12 points each for a total of 24 points

17. Imagine that the earth turns from east to west, so that here in Alabama you see the sun rise in the west and set in the east. On the following diagram of the earth, and given what you know about circulation of the earth's atmosphere and the Coriolis force: draw the major wind patterns that you would expect on the diagram of the earth below (HINT: don’t forget that the winds have both N-S and E-W components to their directions). Also, describe the direction of water circulation in the oceans in the Northern and Southern Hemispheres.

18. Define the concepts of density dependence and density independence. Explain why density independence is important to the exponential model of population growth, and why density dependence is important to the logistic model of population growth. (HINT: you can draw figures to illustrate your definitions and explanations).






20 points each for a total of 40 points

19. Beach voles (Microtus breweri) and meadow voles (Microtus pennsylvanicus) are small North American "field mice" that are closely related to each other. Beach voles occur on islands off the east coast, and have slow growth, late maturity, high survival, and small litters. Meadow voles occur on the continental mainland, and have fast growth, early maturity, low survival, and large litters. Give 2 hypotheses to explain the evolution of these different life histories (HINT: 2 life-history models). Using all of the steps of deduction, design a study to test which of your 2 hypotheses is a better explanation of the differences in life histories that occur on islands and on the mainland. Be sure to describe the critical data you would gather to discriminate between the models. When you finish the above, explain what you would conclude from the following result: you put voles from an island onto the mainland, and find that the island voles exhibit life-history traits that are the same as the mainland voles.





20. Hurricanes can destroy the plant life of coastal beach habitats, virtually cleaning them off to the bare sand. A successional change occurs, however, as the denuded habitat gradually changes back to the typical sand dune vegetation of grasses, wildflowers, and low-growing bushes. Describe two hypotheses of succession that could predict the pattern of change in species over time. Using all the steps of deduction, describe how you would test the 2 hypotheses for the beach community. Be sure to include the specific data that you would need to gather. After you describe your deductive tests, indicate the changes in species richness (S) and diversity (H') that you would expect over time under each hypothesis. Could you predict the species composition of the climax community under these hypotheses? Explain whether these last predictions would be the same or different for the 2 hypotheses.