Spring 2002
Review Problems--Unit 3
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Nature of Communities
1. Communities and species interactions are often described in TV nature shows as part of the "balance of nature." In what ways does this mislead people about the nature of communities? Are there ways in which this idea correctly describes communities?
2. Contrast the views of the "rivet" and "redundancy" models of communities. How do these models relate to the "superorganism" and "individualistic" ideas of communities debated earlier in this century?
3. What is a "keystone" species? Describe how the seastar Pisaster plays this role in rocky intertidal communities.
4. Calculate the index of similarity between the following two communities. (Not covered Spring 2004)
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(Rhododendron Garden) |
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Diversity Measures
5. You are interested in comparing the bird species in three estuaries. You go census the areas and obtain the following counts:
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common tern |
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black tern |
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sooty tern |
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herring gull |
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ring-billed gull |
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Answer the following questions by inspection; there is no need to calculate values for this question.a. Which estuary has the highest richness?
b. Which estuary has the lowest diversity?
6. Three common intertidal species are Pisaster (a sea star), Balanus (a barnacle), and Mytilus (a mussel). On a particular rock, the following numbers of each were found:
Balanus
74 Pisaster
1 Mytilus
25 a. Calculate species richness (S) and the Shannon-Weiner diversisty index (H').
b. If Pisaster were to increase somewhat in relative abundance, how would that change the values for richness and diversity (no change, increase, decrease)?
c. If Balanus were to increase somewhat in relative abundance, how would that change richness and diversity (no change, increase, decrease)?
Island Biogeography
7. Why is MacArthur and Wilson's Island Biogeography model called an equilibrium model? Why does it predict that:
a. large near islands should have more species than small far islands?b. small near islands should have higher turnover rates than large far islands?
8. Distant oceanic islands are known to have many fewer species than the same area would on a mainland. What is the equilibrium explanation for that pattern? What is the non-equilibrium explanation for that pattern?
Intermediate Disturbance Hypothesis
9. Why does the intermediate disturbance hypothesis propose that species diversity should be highest with intermediate frequencies of disturbance?
10. Epiphytes are plants that grow on other plants--the tropics have many species of bromeliads that grow on the branches of trees. These bromeliads often hold water in the center of the plant since they can't get water from the soil. The water pockets inside these bromeliads are ecosystems of their own, complete with predators, prey, competitors, mutualists, etc. Rain adds water to the pockets, but a heavy rain will overflow the pocket and wash away some of the organisms. Let's assume that bromeliads that occur on the outermost branches are most exposed to rain and therefore are more frequently partially washed out, bromeliads on intermediate branches are less often partially washed out, and bromeliads close to the trunk are very rarely partially washed out. In which position would you expect to see the highest diversity of organisms in the bromeliad pockets? Why? How could you investigate the mechanism for any differences in diversity that you observed?
Succession
11. Of the three mechanisms of succession, compare and contrast how each leads to replacement of early successional species by later successional species. Describe how you could test among these three mechanisms.
12. During secondary succession, we find that species diversity first increases and then decreases over time as we approach the climax community. How would you explain this pattern in species diversity over succession in terms of the reasoning of the intermediate disturbance hypothesis?
13. Whereas the mechanisms of succession usually described refers to how later species invade and displace species earlier in the successional successional sequence, there has been less emphasis on what causes the decline of the earlier species after the invasion of later species. Halpern, et al. (1997) investigated why groundsel (Senecio sylvaticus), an annual that becomes extremely abundant in the second year after logging and burning in Oregon forests, abruptly declines in abundance in the third year. They removed potentially competing vegetation [4 removal treatments: control = removal of no neighboring vegetation; removal of fireweed (Epilobium) = the next dominant species in the successional sequence; removal of all other vegetation; or removal of both Epilobium and all other vegetation] in the second and third years and measured the biomass of Senecio on experimental 1 m2 plots. They also measured Senecio density in year 2 and used that as a continuous variable for the analysis in year 3. Some of their data are extracted and reproduced here.
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P-values for ANOVA main effects of removals (compared to control) and their interaction
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The relationship between Senecio density in year 2 and in year 3 is shown below.
a. What is the effect on Senecio biomass of removing Epilobium in year 2? In year 3?b. What is the effect on Senecio biomass of removing all other vegetation in year 2? In year 3?
c. How would you characterize the effect of other vegetation on the third year decline of Senecio?
d. How would you characterize the effect of Senecio in year 2 on its own abundance in year 3?
e. Is there evidence for competition from other species causing the displacement of Senecio in the successional sequence? What are some alternative hypotheses?
Global Patterns in Species Richness
14. Evaluate the ability of each of the following hypotheses to explain the high species diversity of tropical forests.
Productivity
Predictability and specialization
Time
15. Along a gradient of increasing soil nutrients, you find that plant species diversity declines but insect species diversity increases. Develop one hypothesis to explain the pattern for plants and one hypothesis to explain the pattern for insects. Your two hypotheses should be consistent with each other (i.e., your plant hypothesis should not assume anything contradictory to your insect hypothesis and vice versa). In your answer, make sure you state the conditions necessary for that hypothesis to hold and any assumptions you are making.
Equilibrium vs. Non-equilibrium
16. What do ecologists mean by the term "community stability?" What evidence does Tilman present linking species diversity to community stability?
17. What is the fundamental difference between the equilibrium and the non-equilibrium views?
18. What is meant by "top-down control" vs. "bottom-up control?" Which one fits better into the equilibrium context? How can the concept of top-down vs. bottom up help predict the effects of fishing pressure on the top consumers?
Ecosystem Ecology
19. What are gross and net primary productivities?
20. Below are shown trophic level pyramids from two ecosystems that differ in the sizes of the consumer levels.
a.Which ecosystem, 1 or 2, is likely to represent mammalian herbivores and predators? Which one is likely to represent fish? Why?b. Why is the energy transfer rate from primary producers to primary consumers always lower than the transfer rate from primary consumers to secondary consumers?
21. Why can a community with high net primary productivity often support more trophic levels than a community with low primary productivity? Why can aquatic systems often support more trophic levels than terrestrial systems?
22. Herbivorous zooplankton species often show a pattern of daily vertical migration such that they are found deep in the water column in the day but up at the surface at night. The movement to deep water in the day has been shown to be a response to visual predators, mainly fish. Because deep water is dark, fish can't see them as well and the zooplankton in deep water survive better. But why don't the zooplankton just spend all their time in deep water? Why do they come up to the surface at night?
23. Where is most of the world's nitrogen? How does it mainly become available to plants? to animals?
24. How did phosphorus pollution cause algae "blooms" in freshwater lakes before phosphates were eliminated from laundry detergents?
Conservation Biology
25. Explain why a reserve of 1000 km2 in one block might contain more species than 10 reserves of 100 km2 each.
26. Small populations often have low genetic variability. Why is this a problem for preserving the species?
27. What is a minimum viable population? How would MVP change as lifespan increases? How would MVP change as variability in population growth rates increases? (not covered in 2004)
28. How does the minimum area required for a population change with trophic level? How does it change with body size? (not covered in 2004)
29. What are four reasons that small populations are more at risk of extinction than large populations?
30. Summarize the Olympic mountain goat removal controversy. What is your opinion about what, if anything, should be done? What evidence supports that opinion? (not covered in 2004)
31. What are some genes that have been successfully introduced into crop plants? What are the benefits and risks of incorporating genes for herbivore resistance in crop plants? What is your opinion about whether genetic manipulation of crop plants is ok, and what evidence supports that opinion? (not covered in 2004)
32. What are the pros and cons of dam removal intended to aid salmon recovery?