Additional Laboratory Notes for BIO 2020

© 20 April 2004, Mary Jean Holland


Survivorship Curves

In this exercise you will simulate a survivorship curve for a Type III Species. Suppose you start with a cohort of 100 fertilized eggs. Suppose that (1) each individual has only a 15-20% chance of surviving the first week, (2) those surviving the first week have about a 50% chance of surviving the second week, and (3) those surviving to the third week have at least a 95% chance of surviving each week thereafter.

The 100 fertilized eggs are represented by red beans. The survival of each individual each week will be determined by throwing dice. If the dice indicate death, transfer the bean to the beaker marked "cemetery." If the dice indicate survival, transfer the bean to the next week's beaker. Record your data on the sheet provided. Also graph your results, "Number of Survivors" on the ordinate, "Time in Weeks" on the abscissa.

Week One: To determine the survival for each individual, throw FIVE dice. If there is at least one die with a single dot showing, the individual dies during the first week. Repeat this process until all individuals are either dead or have safely reached the second week. Note: The probability of any one die have a single dot is 1/6. When five dice are thrown, the probability of at least one die with single dot is 5/6.
(1/6 + 1/6 + 1/6 + 1/6 + 1/6 = 5/6)

Week Two: To determine the survival for each individual, throw THREE dice. If there is at least one die with a single dot showing, the individual dies during the second week. Repeat this process until all individuals are either dead or have safely reached the third week. Note: The probability of any one die have a single dot is 1/6. When three dice are thrown, the probability of at least one die with single dot is 1/2.
(1/6 + 1/6 + 1/6 = 3/6)

Week Three: To determine the survival for each individual, throw TWO dice. If BOTH dice have a single dot showing (Snake Eyes), the individual dies during the third week. Repeat this process until all individuals are either dead or have safely reached the fourth week. Note: The probability of one die showing a single dot is 1/6. When two dice are thrown, the probability of both dice showing single dot is 1/36.
(1/6 x 1/6 = 1/36)

Weeks Four, Five, Six, etc.: Follow the same procedure as Week Three.

Data Survivorship Curve: Type III Species

Week Number of Survivors
0  
1  
2  
3  
4  
5  
6  
7  
8  
9  
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11  
12  
13  
14  
15  
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20  


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Last updated 20 April 2004 (MJCH/JHW)