Zoology 441 (Animal Ecology)
Practice problems -- competition studies, predation
 

1. What are the two possible results of competition on population size?  How have these been studied in the laboratory?  How do different results obtained relate to outcomes of competition predicted by the Lotka-Volterra competition models?
2. How have exclosure experiments contributed to the study of competition?  What can be shown with exclosure experiments that can not be shown by describing patterns of species distribution?  What are possible problems with exclosure experiments, and how can one control such experiments?
3. Two species of nuthatch, a kind of bird that uses its thin bill to feed on insects under bark, have areas of geographic range that overlap and areas that do not.  Where the two species occur together, their bills differ in length.  Where the two species do NOT occur together, their bills are the same size.  Give two alternate hypotheses, one based on the evolutionary effects of competition and one based on some other factor, that could explain the pattern in bill size.  Suggest how to test between these hypotheses.
4. Two species of anole, a kind of lizard that climbs trees and eats ants off of tree branches, occur together on some islands in the West Indies.  Each species occurs without the other on various other islands. Where they occur together, one species forages on small branches only and the other forages only on tree trunks.  Their foraging behavior on islands where only one species occurs has not been described.
5.  In areas where both occur, you set up some study plots where you remove all the of the trunk-foragers and other study plots where you remove all the branch-foragers. (a) Suppose your results are that when you remove trunk-foragers, the branch foragers start to forage on trunks as well as branches, and when you remove branch-foragers, the trunk-foragers start to forage in the branches as well as trunks.  What does this suggest about competition between the two species? (b) Suppose your results are that removal of one species has no affect on where the other forages.  What does this suggest about current competition between the two species?  How could you explain this based on the "ghost of competition past"?  What could you do to further test the "ghost of competition past" hypothesis for these two species in the West Indies? (c) Explain what controls were necessary for the exclosure experiment you conducted.  Why was each necessary?
6. Define "character displacement" and give an example
7. Will the result of competition generally be to increase or decrease the number of species within a community? Why?
8. What is meant by a functional response?  What is meant by a numerical response?
9. Identify the functional response curves drawn below as type 1, type 2, and type 3.  LABEL the axes.  What predator behaviors result in each of these curves?  Which one can result in a density dependent effect on prey populations?  Under what circumstances would you expect to see such a curve?  Why does it matter, in terms of the impact of predation on prey populations, whether the functional response is density dependent or not?

 

 



10. What does it mean to say that the response of prey to predator populations is density dependent?  Why does it matter, in terms of the impact of predators on the prey population, whether the response is density dependent or not?
11. For the following graph, identify: (a) a stable equilibrium prey population that results from predation (b) a stable equilibrium prey population that results from intraspecific competition in the prey species (c) the range of prey population sizes over which predation has a density dependent effect (d) the range of prey population sizes over which intraspecific competition has a density dependent effect. (e) the range of population sizes over which predation does NOT have a density dependent effect.




12. What does it mean to say the a prey population with large numbers has "escaped from the effects of predation" even though predators are present and are killing individuals of the prey population?
13. Suppose that as a prey population grows larger, predators take a constant proportion of the prey population.  Will predation regulate this prey population? Why/why not?
14. Suppose you study a species of rabbit preyed upon by various large mammalian predators.  In one area, large mammalian predators have been driven extinct by human activities, and there are 90 rabbits per hectare.  In another area, there are high densities of predators, and there are around 88 rabbits per hectare.  In a third area, there are high densities of predators, and there are around 5 rabbits per hectare.  Present an explanation for the differences between the rabbit populations in the different areas based on the model of the impact of predation on prey populations that we have studied in lecture.
15. Explain how functional and numerical responses of predators can combine to result in situations in which predators limit prey population size AND situations in which predators do not limit prey population size.  Relate this explanation to the model of the impact of predation on prey populations that we have studied in lecture.