Zoology 441 (Animal Ecology)
Practice questions -- communities

1. Describe a scenario in which species that do not directly interact benefit each other
2. How can parasites and pathogens be more like abiotic factors than biotic factors in their impact on communities?
3. Contrast facultative and obligate mutualism and give examples of both
4. Describe the mutualistic interaction between the bullthorn acacia and the acacia ants.  How do the ants benefit?  How do the acacias benefit?
5. What is "apparent competition"?  Give an example.
6. How can parasitism affect competitive interactions between species?
7. Distinguish between equilibrium and non-equilibrium hypotheses about community structure.
8. Will the result of competition generally be to increase or decrease the number of species within a community? Why?
9. Why would predation decrease the number of species in a community?  What evidence is there that predation has this effect.  Why would predation increase the number of species in a community?  What evidence is there that predation has this effect?
10. What is a keystone species?  How can a predator be a keystone species?
11. What kinds of species can be keystone species?  Give an example of each kind.
12. Discuss pros and cons of the keystone species concept.
13. Explain how computer simulation of random communities was important in demonstrating the impact of interspecific competition in studies of desert rodent communities.
14. How is competition predicted to affect the physical structure of species that coexist in communities?  Why?
15. You suspect that bald eagles are keystone predators of fish in lake communities.  Bald eagles have died out around some lakes but are abundant around others.  If bald eagles are really keystone predators, how would you expect the species diversity of fish in these lakes to differ?  What would cause this difference?
16. You hypothesize that dragonfly larvae are acting as keystone predators on aquatic invertebrates in stream ecosystems.  Describe an experimental test of this hypothesis based on removals and exclosures; state what different possible results would indicate about your hypothesis.
17. Distinguish between the following non-equilibrium models of community structure: fluctuating environment, density independence, and changing environmental mean.
18. How can spatial heterogeneity modify the impact of competition on a community?
19. If an environment undergoes seasonal fluctuations, it may be able to support more species than would a constant environment. Explain why
20. Explain how the intermediate disturbance hypothesis combines aspects of equilibrium and non-equilibrium models of community structure.
21. Consider three different grassland communities.  One is subject to high levels of human disturbance in the forms of bushhogging, mowing, and dirt bikes.  A second is mowed occassionally.  A third is left unmowed and undisturbed.  Which would you expect to show the highest level of species diversity?  What two factors prevent the other two communities from showing as high levels of species diversity?  Which factor is most important in which community?
22. Fire can be a common disturbance in certain communities.  Suppose you were creating a nature reserve in such a community.  What frequency of fires (high, moderate, none) would you want to have in this reserve in order to have a maximum level of species diversity?  Why might you want to consider factors other than maximum level of species diversity to conserve species in this nature reserve -- what frequencies of fire might you want based on other considerations?
23. Different streams differ in current so some are much more disturbed than others.  How would you expect the numbers of relatively r- versus K-selected species to compare between highly disturbed streams, moderately disturbed streams, and undisturbed streams? Why?
24. According to the MacArthur-Wilson model of island biogeography, the number of species on an island is at an equlibrium between what two processes?
25. The following graph shows the predicted rates of extinction and immigration with number of species for a medium sized island a medium distance from the mainland.  For each of the following islands, draw plots of immigration and extinction predicted compared to this initial island.  Explain why each curve is different for the island that is described.  Use the new curves to determine whether the expected equilibrium number of species is larger or smaller than the originally predicted number. (a) A smaller island at the same distance from the mainland.  (b) a larger island at the same distance from the mainland.  (c) An island of the same size that is closer to the mainland.  (d) An island of the same size that is more distant from the mainland.
26. How does the MacArthur Wilson island biogeography model explain the observed increase in number of species with increasing area of islands?  What are other hypotheses that could explain the same thing?  How could one test between these?
27. What are two ways to define the stability of a community?
28. Why is it difficult to evaluate the impact of species diversity on stability?
29. Why are there more species per area in the tropics than in temperate zones?  Give the hypotheses we've discussed in class; evaluate them -- which could be complete explanations, which could explain part but not all of the pattern, and which have some support?