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← 04-30 Two Types of Fish

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Showing Revision 2 created 10/24/2012 by Amara Bot.

  1. Let's consider the first one, two fish of type 1 die.
  2. This expression pretty much looks like it,
  3. but then again it appears here with a plus sign for f₂,
  4. so this rather models that fish of type 1 become fish of type 2 after a certain time.
  5. Remember the SIR model for contagious diseases
  6. where a person is moved from one compartment to another compartment.
  7. No, fish of type 1 don't die. It's rather that we have two types of fish.
  8. The first type becomes the second type after a while--young fish and mature fish.
  9. This growth rate can model both births and deaths.
  10. It takes care of the difference, so in a way
  11. we have taken care of deaths and births from the beginning.
  12. What about our fish of type 2--harvested or not?
  13. We've already explained the first term. What about the second one?
  14. At least, this is not constant harvesting.
  15. For constant harvesting, we should be subtracting constant rate so and so many tons per year.
  16. This could be, however, harvesting that's proportional to the
  17. actual amount of fish, maybe just every second fishes being harvested,
  18. All in all, however, the second term looks like that fish of type 2 died of old age.