Sample Questions for Final Exam

(Modified from 2001 Final)

All questions can be answered with no more than a scientific calculator.

All the questions on this exam relate to a series of studies on the reproductive biology of the chartreuse-footed booby. The males in this species come in two forms, white-winged and black-winged. Females mate with one male and then lay eggs.

(Yes, I seem to write a lot of questions about birds with different colored wings. Apparently my imagination is stuck in a rut.)

1. A complete survey of your population finds that 80% of males are white-winged and 20% are black-winged. You want to know if females favor one form over the other when mating.

   1. The first three females you observe all mate with black-winged males. What is the probability of getting this combination (three blacks in a row) by chance?
      
      
      
      
      
   2. Ultimately, observations of 100 matings among random females found that 70 were with white-winged males and 30 were with black-winged males. Carry out an appropriate test of the null hypothesis that females mate with males at random.
      
      
      
      
      
      
      
2. The next question you ask is whether the number of eggs laid by a female depends on the wing color of her mate. You randomly select 15 females that mated with black-winged males and 15 that mated with white-wings. The summary data was as follows:
   

   Black-wing maters: Mean = 6.6, SD = 1.4
   White-wing maters: Mean = 5.8, SD = 1.1
   

   Is there a significant difference between these two groups?
   
   
   
   
   
   
   
3. You now wonder whether there may be competition among females for mates. With the idea that body size might contribute to a female's competitive ability, you look to see whether there is a difference in body size between females that mate with black-winged versus white-winged males. You also decide to include females that do not mate at all, with the idea that these females would be the least competitive. You randomly select eight females of each type and weigh them, giving you a mass for each animal. What method of analysis would you use on these data?
   
   
   
   
   
   
4. Let's assume your results from the above experiments suggest that: a) mate choice might be important in determining the number of eggs a female lays, and b) that female size is related to mate choice. You would like to know whether it might be the difference in female size between groups that is driving the differences in clutch size. Being busy yourself, you hand off the data to Chim-Chim, the lab chimp, who brings back the results below in exchange for a banana. Alas, Chim-Chim cannot speak, and you must interpret the tables yourself. What sort of analysis did Chim-Chim do, and what to the results indicate?
   

   Source	SS	DF	MS	F	P
   Mate Color	1.929	1	1.929	0.752	0.392
   Mass	42.068	1	42.068	16.403	0.001
   Mate Color x Mass	3.762	1	3.762	1.467	0.234
   Error	92.326	36	2.565

   
   

   Source	SS	DF	MS	F	P
   Mate Color	5.458	1	5.458	2.102	0.156
   Mass	44.661	1	44.661	17.197	0.001
   Error	96.089	37	2.597

   
   
   
   
   
   
   
   
   
   
5. A potential weakness of all your work to date is that it is observational, so it is difficult to know for certain whether the patterns you are finding in your studies represent true cause-and-effect relationships. Assuming you could capture the birds, and keep and breed them under controlled conditions, what sort of experiment(s) might you do to see whether
    
1. females prefer white-winged or black-winged males
2. female body size affects their ability to get mates of a particular color
3. male wing color influences clutch size
4. female body size influences clutch size.
   

Briefly discuss the experimental setups and the analyses you would use on the resulting data. Consider that you may need to control some variables while examining others.