This model illustrates the theory that Native Americans who arrived in the new
world 10,000 years ago may have been responsible for the extinction of the large
mammals of the Americas such as the American lion, tiger and mammoth. This theory
is advanced by Jared Diamond in his book: "The Third Chimpanzee". The basic
premise of the theory is that American large mammals evolved without human
contact, so they were tame and unafraid of the migrating humans, allowing a high
probability of successful hunting by the humans. This could account for the very
rapid simultaneous extinction of all American large mammals at roughly the same
time as the human arrival.

SETUP initializes the mammoths and people. N-MAMMOTHS sets the initial number of
mammoths.  Note that the actual number of mammoths created is less than this,
because the ones created in the oceans immediately die.  The COUNT-MAMMOTH
monitor shows that actual number of mammoths. N-HUMANS slider sets the initial
number of human hunters. GO starts and stops the simulation.

KILL-ODDS: the odds that when a human encounters a mammoth, it will die MAM-BR:
the likelihood of a mammoth reproducing (at a given tick (or moon)) - the mammoth
birth rate HUMAN-BR:the likelihood of a human reproducing (at a given tick (or
moon)) - the human birth rate

STAY-IF-PLENTY?: if this switch is TRUE (0), then the humans do not migrate if
there are plenty of mammoths in their neighborhood. If the switch is FALSE, they
migrate at the same rate regardless of the mammoth density. The definition  of
plenty is governed by the PLENTY slider.


YEARS displays elapsed years in the model. COUNT-HUMAN shows the current number
of humans, and  COUNT-MAMMOTH the current number of mammoths. These counts are
also dynamically plotted in the Population Sizes plotwindow.

Notice the rate of migration of the humans. How does that affect the population
of mammoths?

Notice the rate of mammoth decline. How many years does it take for them to go

Vary the KILL-ODDS. How deos that affect the mammoth population?

Try both settings of the STAY-IF-PLENTY switch. How does the migration pattern of
the humans affect the mammoths?

Make separate monitors for North and South America.

What if Central America weren't so narrow?  Do you think that it, or other
geographical features, could block human hunters the way this model does?

How would adding islands affect the model?

Note the use of nsum to calculate the number of mammoths in the neighborhood

nsum mammoth-present mammoths-in-area

This model is based on the theory expounded by Jared Diamond in:
Diamond, J. (1993). The Third Chimpanzee. Basic Books.