---huntergatherers.nlogo

NETLOGO

  ;; Plot the total number of turtles
  
  set-current-plot "Number of Turtles"
  set-current-plot-pen "Turtles"
  plot count turtles

end

to plot-energy-of-turtle-0

  ;; Plot the energy of turtle 0
  
  set-current-plot "Turtle 0"
  set-current-plot-pen "default"
  plot myEnergyLevel-of turtle 0

end
@#$#@#$#@
GRAPHICS-WINDOW
365
11
726
393
17
17
10.03
1
10
1
1
1

CC-WINDOW
18
310
356
392
Command Center

BUTTON
272
11
338
44
Setup
setup
NIL
1
T
OBSERVER
T

BUTTON
273
50
338
85
Go
go
T
1
T
OBSERVER
T

PLOT
258
401
491
555
Patch Energy Levels by Type
Time
Energy
0.0
100.0
0.0
70.0
true
false
PENS
"Forest" 1.0 0 -11352576 true
"Plains" 1.0 0 -16777216 true

SLIDER
14
10
186
43
numberOfTurtles
numberOfTurtles
0
100
4
1
1
NIL

BUTTON
274
92
337
125
Step
go
NIL
1
T
OBSERVER
T

PLOT
17
401
246
554
Number of Turtles
Time
Turtles
0.0
100.0
0.0
20.0
true
false
PENS
"Turtles" 1.0 0 -16777216 true

SLIDER
16
158
218
191
maxForestGrowthLimit
maxForestGrowthLimit
0
3000
1500
1
1
NIL

SLIDER
14
46
186
79
maxTurtleEnergy
maxTurtleEnergy
0
1000
610
1
1
NIL

SLIDER
17
234
215
267
maxPlainsGrowthLimit
maxPlainsGrowthLimit
0
1500
200
1
1
NIL

SLIDER
14
82
186
115
amountTurtlesEat
amountTurtlesEat
0
500
210
1
1
NIL

SLIDER
15
120
188
153
amountTurtlesBurn
amountTurtlesBurn
0
500
200
1
1
NIL

SLIDER
17
196
205
229
amountForestsRecover
amountForestsRecover
0
20
1
1
1
NIL

SLIDER
18
272
196
305
amountPlainsRecover
amountPlainsRecover
0
50
1
1
1
NIL

@#$#@#$#@
WHAT IS IT?
-----------
This model represents a number of hunter-gatherer bands in an environment that represents forest and plains areas.


HOW IT WORKS
------------
Turtles (hunter-gatherer bands) burn energy every turn and they try to eat every turn to gain energy.  When they eat, they degrade the environment which then recovers at a slower rate.  Turtles have a maximum energy limit, above which they stop growing.

The amount of foliage in the environment is color-coded.  The more green a patch is, the more foliage (energy) is has.  Forest areas start very green and Plains start much less green, by default.  Each type of environment has a maximum energy limit, above which it stops growing.  Similarly, each type of environment has a recovery rate.  If a forest is degraded below a certain threshold level, it will change to a plains environment type and therefore not recover as much.

Each turtle tries to find a place to go on the next turn by choosing a semi-cardinal patch from their current patch.  Turtles will randomly choose one of the patches with the most energy (food).  Turtles leave tracks, which expire after a while.  Turtles are xenophobic in that they will avoid other turtles' tracks, which can override the search for high-energy patches.  If no food can be found elsewhere, hunger overrides xenophobia.  


HOW TO USE IT
-------------
Click the "Setup" button to randomly place some turtles in the environment.  Click the "Go" button to run the model continuously and the "Step" button to run it one turn at a time.

The number of turtles in the model is set with the numberOfTurtles slider (4 by default).  Four turtles is a stable population for the default environment size and variable settings.

The remainder of the variables are closely interrelated!  Please play with them, but do not be surprised if the model varies wildly once they are changed.  It is the relative proportions of these variables more than their individual amplitudes that matters.

The maximum amount of energy that a turtle may have is set with the maxTurtleEnergy slider.


THINGS TO NOTICE
----------------
Turtles will degrade the environment and the environment will (more slowly) recover.  The total energy of the environment will drop until it finds a new equilibrium energy level.

Turtles that start on the plains will (by default) not be able to extract enough energy to live.  Therefore, their search for food will either end in death by starvation or in a move to the forest.

Note that turtles in the forest will tend to stay in the forest.  They will appear to "bounce off" of the forest-plain boundary due to the search for patches with available food.

If the amountTurtlesEat/Burn are the same, they can't make up for lost energy.  Therefore, turtle populations are unstable and will always eventually die.


THINGS TO TRY
-------------
Increase the number of turtles and run the simulation.  If too many turtles try to share the environment, some (or all) of them will die.  If the simulation starts with  more turtles than the equilibrium level, the environment will degrade rapidly, causing the death of many turtles.  Once the excess turtle population has been removed, the environment will recover to a new equilibrium state, defined by a stable energy level over time.  That energy level will be proportional to the number of remaining turtles.

If the number of turtles is increased drastically (try 100), the environment will degrade so rapidly as to kill all turtles.  The environment will eventually recover, although some parts of the forest may have been damaged and only recover to the energy level of plains.

Try starting the simulation with turtles on the plains vs in the forest.  What happens to the turtles on the plains?  By default, turtles cannot live on the plains for long so their search for food either ends in starvation or in a move to the forest.