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Hoofin It!
Activity 12:
Population Calculation

Students use actual 1986-2002 data to graph and analyze sheep population numbers and changes.

Before You Begin:

• Provide each student with a copy of the Population Calculation data . Print out a set of example graphs to check the student work.
  

Procedures:

• Hand out a copy of the Population Calculation data sheet to each student, and briefly review the type of data that it includes.
  
  
• Discuss with the students what types of scientific questions they can ask about population sizes. Discuss that researchers use different types of investigations to answer different types of questions. Which of the questions the students think of can be answered by a population survey?
  
  Refering to Population Calculation data have the class develop together a list of questions that can be answered with the data. Augment with the discussion questions below.
  
  Which if any of these questions can students guess a reasonable answer, and which require data to investigate?
  
  
• Students create a series of graph (x-y or bar chart style), where the year from 1986-2002 is along the x-axis.
1. Total population (adults + lambs + unknown)
2. Adult population (rams + ewes)
3. Number of ewes
4. Number of rams
5. Number of lambs
6. Percent change in total population
   (population this year - population last year) / population last year *100



• Students provide answers to each of the questions listed by the class.
  
  
• As a class, review the answers and discuss explanations or further research questions that follow from the questions and answers. How do scientists combine data/observations and knowledge they already have (such as from Dall Sheep Population Size) to develop new understandings?
  
  
• Why would scientists want to make the information they learn about Dall sheep populations, public? [other scientists can do further research, managers can protect populations, people (like the students themselves) can learn about Dall sheep, etc.]

Discussion Questions:

1. Which year had the highest total population of sheep? Which year the lowest?
   
   
2. Did the number of rams, ewes and lambs have their highest and lowest population in the same years?
   
   
3. What was the maximum total population from 1986-2002? The minimum, the mean, the range? What about for all adults, for ewes, rams, and lambs?
   
   
4. During which years did the total population rise, and during which years did it fall?
   
   
5. Are there more rams, ewes or lambs in the population? Why might that be?
   
   
6. Which population curve, ewes, lambs or rams, does the total population curve look the most like? Why is that?
   
   
7. Using the graph of Percent Change in Population, which years were the hardest and which were the best for the Dall sheep? Are these the same years when the total population was the highest or lowest, or different years? Why?
   
   
8. What environmental factors could cause the changes in Dall sheep population?
   
   
9. If you wanted to know how snow, predation, and hunting affect the Dall sheep population, what would you measure? For each one, how would you expect the measurement to vary across the years (1986-2002) if it were an important factor? If it were not an important factor?
   

Adaptations:

• Break students into 6 groups, and assign one graph to each group. Have students in each group do their graphing independently.
  
  
• Have students calculate for themselves: All rams, Adults, Total, and Percent change (of total).
  
  
• Computer lab: download the Population Calculation data in text format or Excel format. Have students use spreadsheet software to create the graphs. Students can also use the spreadsheet functions to calculate.
  
  
• To concentrate on reading graphs rather than creating graphs, review the discussion questions using the Population Calculation graphs already generated.

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