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Trial 3 - Extinction

1. In the long history of life on Earth, many species have come and gone. For example, dinosaurs were around for many millions of years, but now they are entirely extinct. What are some events that could cause extinction of a population?
   
   

2. Now observe extinction by changing the variables in this model. Open the model. See Technical Hints to run and save the evolution model. Here are some questions for you to explore.

   [model: populationA]

3. Run the model. Gradually reduce GRASS-REGROWTH-RATE. At what value is extinction quite likely?
   
   
4. Return GRASS-REGROWTH-RATE to 80. Gradually reduce INITIAL-NUMBER. You must hit SETUP and start again each time you change it. At what value is extinction quite likely?
   
   
5. Return INITIAL-NUMBER to 100. Run the model and gradually reduce GAIN-FROM-FOOD. At what value is extinction quite likely?
   
   
6. Here is a summary of your results. Make a composite chart of the findings for the whole class. Why might the answers vary from different teams?
   

   Variable	Value causing extinction
   Initial-number
   Grass-regrowth-rate
   Grain-from-food
   Birthrate-%

   
   

7. Now that you know the effects of the different variables, here's a challenge. Open the model.

   [model: populationC]

8. The sheep rancher wants to sell off as many sheep per year as possible. What's the largest number he can remove without losing his flock? (hint: use the NUMBER-REMOVED slider to control how many the rancher removes each year.) In this model, the sheep flash blue just before they are removed. You can change all of the variables. Record the highest NUMBER-REMOVED the rancher can maintain without losing the flock, and the strategy you used to get the highest possible yield.

   Best NUMBER-REMOVED =

   

   Strategy: