Wednesday, February 4, 2015

Scientific Method Case Study (Bowhead Whale Example)

I made a case study activity to use get my Biology students to think about the scientific method. This is research from my dissertation. Any feedback for improving it would be great! Feel free to use in your classroom, or just for fun!!

Here is a link to the pdf for easier printing  link to pdf



The Bigger the Momma, the Better: A Case Study Reviewing the Scientific Method
Bowhead whales (Balaena mysticetus) belong to a group of whales called mysticetes or baleen whales. Bowhead whales live in the Arctic waters of Alaska, Canada, Greenland, and Russia. They used their baleen like a strainer to filter out and capture krill. They are a very large and rotund with heads that are 1/3 the size of their body (See picture above). They are also the only whale that lives in the Arctic year-round. All females of baleen whales are larger than males, on average. The reason for why baleen whales are sexually dimorphic is unclear. 

What are some observations made from this background information on bowhead whales?





Why do you think female bowhead whales are larger than male bowhead whales?





One hypothesis as to why females are larger than males is called the big mother hypothesis. The big mother hypothesis is that bigger mothers are better mothers because they can allocate more resources to their young. In the case of bowhead whales, calves are 4 meters at birth, weigh 2000 lbs, and grow approximately 1 cm of length per day. During this growth they eat nothing but their mother’s milk until they are weaned after around 12 months. That’s a lot of energy being transferred! Bowhead whale milk is 50% fat, can you imagine taking a gulp of milk that is 50% fat? 


Baleen is made of keratin and is similar to the structure of fingernails. Baleen grows from the gums of bowhead whales continuously. One piece of baleen can have up to 20 years of growth from end to end. Reproductive hormones such as progesterone will increase in circulation when a female is pregnant and can be measured in baleen. Thus baleen can be used to detect pregnancies in bowhead whales over time. By counting pregnancies in a piece of baleen a pregnancy rate (number of years between pregnancies on average) can be calculated. 

A large piece of baleen from a bowhead whale.

What would you expect the relationship between pregnancy rate and length of a female to be if the big mother hypothesis is accurate? Circle the line that would best fit the hypothesis.

Here is some actual data as calculated by the hormones in baleen.
Female Whales
Length (meters)
Pregnancy Rate (years)
Age (years)
00B5
17.5
3.225
64.1
05S5
16.5
3.86
47.4
86KK2
17.2
4.52
53
87B5
15.7
4.625
51
87B6
15.7
3.5952381
53
88B11
15.6
4.4

88G1
15.7
4.25
46
88KK1
14.9
5.3889
39
90G4
15.2
4.104

11B6
16.9
3.09
71.3
86WW2
17.7
5.17
34
89B7
14.6
3.86

87N1
15.2
3.595

05S6
17.1
3.49

05S7
18
3.275
81.5

Graph the relationship between length and pregnancy rate by making a scatterplot in the figure below
How does the actual graph compare to your proposed graph? If it is different why do you think that is?

Results: The statistical significance of this correlation is measured by a p-value. A p-value of less than 0.05 would mean that this relationship is statistically significant. The p-value of the relationship between pregnancy rate and length is 0.170.
Conclusion and interpretation:


Does the data from your results support the big mother hypothesis?



Now Graph the relationship between calving rate and age
Results: The statistical significance of this correlation is measured by a p-value. A p-value of less than 0.05 would mean that this relationship is statistically significant. The p-value of the relationship between pregnancy rate and age is 0.001.

Does the data from your results support the big mother hypothesis? If not, what is an alternative hypothesis?




What conclusions can be made from this study?



What type of study is this?


Does this mean the big mother hypothesis is wrong (Explain)?


What would you change or do to improve this study and/or increase the confidence of our results?


What is the importance of this study (what are practical uses for this information)?



1 comment:

  1. Sam Hirt's research has changed my life. He is a great American hero.

    ReplyDelete