Stephen G. Saupe - Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321; (320) 363-2782; ssaupe@csbsju.edu

Gink & Go Watch Survivor

Setting:  Thursday evening. 7:15 pm.  TV Lounge.  Gink is sitting on a sofa in front of the tube watching "Survivor."  Go walks into the room clutching his biology book and sits on another sofa.

Go:   Hey Gink, what are you watching?
Gink:   My favorite show....so don't bother with any anything having to do with Saupe�s stupid biology class.
Go:   But we discussed "Survivor" in class. 
Gink:   We did?  No way.
Go:   Way.
Gink:   I must've been asleep - Saupe does that to me, you know.
Go:   Right....while you were dozing we talked about survivorship curves and used "Survivor" as example of one of them.
Gink:   Whoa, backup.  What's a survivorship curve?  Does it involve tribes, reward challenges and voting people off the island?
Go:   Not exactly...a survivorship curve is a graph of the number of individuals in a cohort that survive over time.  
Gink:   So what's a cohort?  Sounds like the name of one of the tribes.  I wonder what colored buffs they have?
Go:   Focus for a minute.  A cohort is a group.  Population biologists use it to describe a group of individuals that were born at the same time.
Gink:   And they study this cohort and calculate the percentage of individuals remaining after different time intervals. 
Go:   That's right.  They could just as easily plot mortality curves since that's the inverse of survivorship, but it's a little morbid.
Gink:   Yeah, no one would watch a show called "Morbidity."
Go:   There are actually three different types of survivorship curves.
Gink:   Make it quick dude - the immunity challenge is almost on.
Go:   Okay, okay.  In Type I survivorship curves most of the cohort  survive and reach a ripe old age and then die.  There is very little infant mortality.
Gink:   Just like people. 
Go:   Exactly.  And type III curves result when there is very high infant mortality.  Very few individuals in the cohort survive.
Gink:   This reminds me of oak trees.  They make oodles of acorns but very few seedlings ever grow into a mighty oak.
Go:   You've got it.  Type II is where there is a uniform death rate.  There is no greater chance of individuals dying at any point during their lifespan.
Gink:   Oh, that�s just like Survivor!  The number of contestants decreases at a consistent rate during each episode. 
Go:   And it is also a feature of many mammal populations 
Gink:   Good, now go away so I can finish watching in peace - or I'll have Jeff Probst snuff out your torch.
Go:   Alright, but first let�s draw the graphs (complete the questions/graphs below)

 

    

Graph Summary:  In the space below, draw the three types (I, II, III) of survivorship curves.  Label the Y axis (% surviving) and X axis (time).  Be sure to label each graph with a I, II or III.

 

 

 

 

 

 

 

 

Questions:

 

  1. Define cohort.
     

  2. Define survivorship.
     

  3. Which curve (I, II, III) would be expected in the following cases?:

    _____ a population has a high rate of infant mortality

    _____ population of birds

    _____ a population of whales or dolphins

    _____ population with lots of maternal care

    _____ population with high reproductive output (many small offspring)

    _____ population that generally lives to its maximum life expectancy

     

  4. Describe a way that the TV show "Survivor" could be modified and played to model a type I survivorship curve.




     

  5. Describe a way that the TV show "Survivor" could be modified and played to model a type III survivorship curve.


     
     

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Last updated: April 06, 2004   
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