globals [coin]
turtles-own [age missionaccomplished?]
breed [dominants dominant]
breed [heterozygotes heterozygote]
breed [recessives recessive]
;;;;;
;; Basic Setup
;;;;;
to startup
setup
end
to setup
ca
if randomtraits? = false ;; Creates turtles based on user-selected distributions of genotypes
[create-dominants #dominants
create-heterozygotes #heterozygotes
create-recessives #recessives]
if randomtraits? = true ;; Creates turtles with a random distribution of genotypes
[create-dominants random 10
create-heterozygotes random 10
create-recessives random 10]
ask dominants [set color blue ;; Gives homozygous dominant turtles a blue phenotype
set xcor random-xcor
set ycor random-ycor]
ask heterozygotes [set xcor random-xcor ;; Gives heterozygous turtles either a blue or a green phenotype
set ycor random-ycor
ifelse showasdifferent? = true [set color green] [set color blue]]
ask recessives [set color yellow ;; Gives homozygous recessive turtles a yellow phenotype
set xcor random-xcor
set ycor random-ycor]
ask turtles [set age 0
set missionaccomplished? false]
end
to go
if count turtles < 2 [stop clear-turtles] ;; Makes sure there are enough turtles in the world to reproduce and increase the population size
move
reproduce
getolder ;; See "Components of "Go"" below for details
expire
update-plot
tick
end
;;;;;
;; Components of "Go"
;;;;;
to move ;; Turtles move randomly
ask turtles [rt random 360
fd 1]
end
to reproduce ;; When two turtles who have reached the user-set reproductive age land on the same patch,
ask turtles [if count dominants-here = 2 ;; they produce a single new turtle with a genotype determined by the rules of Mendelian Genetics
and age > reproage
[hatch-dominants 1 [set age 0 set color blue set missionaccomplished? false] set missionaccomplished? true]]
ask turtles [if count dominants-here = 1 and count heterozygotes-here = 1
and age > reproage
[set coin one-of (list 0 1)
if coin = 0 [hatch-heterozygotes 1 [set age 0 ifelse showasdifferent? = true [set color green] [set color blue] set missionaccomplished? false] set missionaccomplished? true]
if coin = 1 [hatch-dominants 1 [set age 0 set color blue set missionaccomplished? false] set missionaccomplished? true]]]
ask turtles [if count dominants-here = 1 and count recessives-here = 1
and age > reproage
[hatch-heterozygotes 1 [set age 0 ifelse showasdifferent? = true [set color green] [set color blue] set missionaccomplished? false] set missionaccomplished? true]]
ask turtles [if count recessives-here = 2
and age > reproage
[hatch-recessives 1 [set age 0 set color yellow set missionaccomplished? false] set missionaccomplished? true]]
ask turtles [if count recessives-here = 1 and count heterozygotes-here = 1
and age > reproage
[set coin one-of (list 0 1)
if coin = 0 [hatch-heterozygotes 1 [set age 0 ifelse showasdifferent? = true [set color green] [set color blue] set missionaccomplished? false] set missionaccomplished? true]
if coin = 1 [hatch-recessives 1 [set age 0 set color yellow set missionaccomplished? false] set missionaccomplished? true]]]
ask turtles [if count heterozygotes-here = 2
and age > reproage
[set coin one-of (list 0 1 1 2)
if coin = 0 [hatch-dominants 1 [set age 0 set color blue set missionaccomplished? false] set missionaccomplished? true]
if coin = 1 [hatch-heterozygotes 1 [set age 0 ifelse showasdifferent? = true [set color green] [set color blue] set missionaccomplished? false] set missionaccomplished? true]
if coin = 2 [hatch-recessives 1 [set age 0 set color yellow set missionaccomplished? false] set missionaccomplished? true]]]
end
to getolder ;; Turtles age in order to reach reproductive age and ultimately die
ask turtles [set age age + 1]
end
to expire ;; Turtles do not last forever. Their death rate is proportionate to their population size
ask turtles [if missionaccomplished? = true and random (maxnumber) < (count turtles) [die]]
end
;;;;;
;; Selection Methods
;;;;;
to bottleneck ;; Allows the user to kill off 3/4 of the population at random with a single click
ask turtles [set age 0]
ask turtles [if ByLocation? = true [if xcor > 1 or ycor < 1 [die]]] ;; Kills turtles within Quadrants I, III and IV
if ByLocation? = false [ask n-of (round (count turtles * .75)) turtles [die]] ;; Kills 3/4 of the turtles at random
update-plot
end
to select ;; Allows the user to put as much selection pressure as they desire on any or all of the genotypes
if selectionvictims = "recessives" [ask recessives [set coin one-of (list 1 2 3 4 5 6 7 8 9 10)
if ( recessive-survival? = 0 and ( coin != 0 )) or
(recessive-survival? = 10 and ( coin != 1 )) or
(recessive-survival? = 20 and ( coin != 1 and coin != 2 )) or
(recessive-survival? = 30 and ( coin != 1 and coin != 2 and coin != 3 )) or
(recessive-survival? = 40 and ( coin != 1 and coin != 2 and coin != 3 and coin != 4 )) or
(recessive-survival? = 50 and ( coin != 1 and coin != 2 and coin != 3 and coin != 4 and coin != 5 )) or
(recessive-survival? = 60 and ( coin = 1 or coin = 2 or coin = 3 or coin = 4 )) or
(recessive-survival? = 70 and ( coin = 1 or coin = 2 or coin = 3 )) or
(recessive-survival? = 80 and ( coin = 1 or coin = 2 )) or
(recessive-survival? = 90 and ( coin = 1 )) or
(recessive-survival? = 100 and ( coin = 0 )) [die]]]
if selectionvictims = "dominants" [ask dominants [set coin one-of (list 1 2 3 4 5 6 7 8 9 10)
if ( dominant-survival? = 0 and ( coin != 0 )) or
(dominant-survival? = 10 and ( coin != 1 )) or
(dominant-survival? = 20 and ( coin != 1 and coin != 2 )) or
(dominant-survival? = 30 and ( coin != 1 and coin != 2 and coin != 3 )) or
(dominant-survival? = 40 and ( coin != 1 and coin != 2 and coin != 3 and coin != 4 )) or
(dominant-survival? = 50 and ( coin != 1 and coin != 2 and coin != 3 and coin != 4 and coin != 5 )) or
(dominant-survival? = 60 and ( coin = 1 or coin = 2 or coin = 3 or coin = 4 )) or
(dominant-survival? = 70 and ( coin = 1 or coin = 2 or coin = 3 )) or
(dominant-survival? = 80 and ( coin = 1 or coin = 2 )) or
(dominant-survival? = 90 and ( coin = 1 )) or
(dominant-survival? = 100 and ( coin = 0 )) [die]]]
if selectionvictims = "heterozygotes" [ask heterozygotes [set coin one-of (list 1 2 3 4 5 6 7 8 9 10)
if ( heterozygote-survival? = 0 and ( coin != 0 )) or
(heterozygote-survival? = 10 and ( coin != 1 )) or
(heterozygote-survival? = 20 and ( coin != 1 and coin != 2 )) or
(heterozygote-survival? = 30 and ( coin != 1 and coin != 2 and coin != 3 )) or
(heterozygote-survival? = 40 and ( coin != 1 and coin != 2 and coin != 3 and coin != 4 )) or
(heterozygote-survival? = 50 and ( coin != 1 and coin != 2 and coin != 3 and coin != 4 and coin != 5 )) or
(heterozygote-survival? = 60 and ( coin = 1 or coin = 2 or coin = 3 or coin = 4 )) or
(heterozygote-survival? = 70 and ( coin = 1 or coin = 2 or coin = 3 )) or
(heterozygote-survival? = 80 and ( coin = 1 or coin = 2 )) or
(heterozygote-survival? = 90 and ( coin = 1 )) or
(heterozygote-survival? = 100 and ( coin = 0 )) [die]]]
if selectionvictims = "allbutrecessives" [ask dominants [set coin one-of (list 1 2 3 4 5 6 7 8 9 10)
if ( dominant-survival? = 0 and ( coin != 0 )) or
(dominant-survival? = 10 and ( coin != 1 )) or
(dominant-survival? = 20 and ( coin != 1 and coin != 2 )) or
(dominant-survival? = 30 and ( coin != 1 and coin != 2 and coin != 3 )) or
(dominant-survival? = 40 and ( coin != 1 and coin != 2 and coin != 3 and coin != 4 )) or
(dominant-survival? = 50 and ( coin != 1 and coin != 2 and coin != 3 and coin != 4 and coin != 5 )) or
(dominant-survival? = 60 and ( coin = 1 or coin = 2 or coin = 3 or coin = 4 )) or
(dominant-survival? = 70 and ( coin = 1 or coin = 2 or coin = 3 )) or
(dominant-survival? = 80 and ( coin = 1 or coin = 2 )) or
(dominant-survival? = 90 and ( coin = 1 )) or
(dominant-survival? = 100 and ( coin = 0 )) [die]]
ask heterozygotes [set coin one-of (list 1 2 3 4 5 6 7 8 9 10)
if ( heterozygote-survival? = 0 and ( coin != 0 )) or
(heterozygote-survival? = 10 and ( coin != 1 )) or
(heterozygote-survival? = 20 and ( coin != 1 and coin != 2 )) or
(heterozygote-survival? = 30 and ( coin != 1 and coin != 2 and coin != 3 )) or
(heterozygote-survival? = 40 and ( coin != 1 and coin != 2 and coin != 3 and coin != 4 )) or
(heterozygote-survival? = 50 and ( coin != 1 and coin != 2 and coin != 3 and coin != 4 and coin != 5 )) or
(heterozygote-survival? = 60 and ( coin = 1 or coin = 2 or coin = 3 or coin = 4 )) or
(heterozygote-survival? = 70 and ( coin = 1 or coin = 2 or coin = 3 )) or
(heterozygote-survival? = 80 and ( coin = 1 or coin = 2 )) or
(heterozygote-survival? = 90 and ( coin = 1 )) or
(heterozygote-survival? = 100 and ( coin = 0 )) [die]]]
if selectionvictims = "allbutdominants" [ask recessives [set coin one-of (list 1 2 3 4 5 6 7 8 9 10)
if ( recessive-survival? = 0 and ( coin != 0 )) or
(recessive-survival? = 10 and ( coin != 1 )) or
(recessive-survival? = 20 and ( coin != 1 and coin != 2 )) or
(recessive-survival? = 30 and ( coin != 1 and coin != 2 and coin != 3 )) or
(recessive-survival? = 40 and ( coin != 1 and coin != 2 and coin != 3 and coin != 4 )) or
(recessive-survival? = 50 and ( coin != 1 and coin != 2 and coin != 3 and coin != 4 and coin != 5 )) or
(recessive-survival? = 60 and ( coin = 1 or coin = 2 or coin = 3 or coin = 4 )) or
(recessive-survival? = 70 and ( coin = 1 or coin = 2 or coin = 3 )) or
(recessive-survival? = 80 and ( coin = 1 or coin = 2 )) or
(recessive-survival? = 90 and ( coin = 1 )) or
(recessive-survival? = 100 and ( coin = 0 )) [die]]
ask heterozygotes [set coin one-of (list 1 2 3 4 5 6 7 8 9 10)
if ( heterozygote-survival? = 0 and ( coin != 0 )) or
(heterozygote-survival? = 10 and ( coin != 1 )) or
(heterozygote-survival? = 20 and ( coin != 1 and coin != 2 )) or
(heterozygote-survival? = 30 and ( coin != 1 and coin != 2 and coin != 3 )) or
(heterozygote-survival? = 40 and ( coin != 1 and coin != 2 and coin != 3 and coin != 4 )) or
(heterozygote-survival? = 50 and ( coin != 1 and coin != 2 and coin != 3 and coin != 4 and coin != 5 )) or
(heterozygote-survival? = 60 and ( coin = 1 or coin = 2 or coin = 3 or coin = 4 )) or
(heterozygote-survival? = 70 and ( coin = 1 or coin = 2 or coin = 3 )) or
(heterozygote-survival? = 80 and ( coin = 1 or coin = 2 )) or
(heterozygote-survival? = 90 and ( coin = 1 )) or
(heterozygote-survival? = 100 and ( coin = 0 )) [die]]]
if selectionvictims = "allbutheterozygotes" [ask dominants [set coin one-of (list 1 2 3 4 5 6 7 8 9 10)
if ( dominant-survival? = 0 and ( coin != 0 )) or
(dominant-survival? = 10 and ( coin != 1 )) or
(dominant-survival? = 20 and ( coin != 1 and coin != 2 )) or
(dominant-survival? = 30 and ( coin != 1 and coin != 2 and coin != 3 )) or
(dominant-survival? = 40 and ( coin != 1 and coin != 2 and coin != 3 and coin != 4 )) or
(dominant-survival? = 50 and ( coin != 1 and coin != 2 and coin != 3 and coin != 4 and coin != 5 )) or
(dominant-survival? = 60 and ( coin = 1 or coin = 2 or coin = 3 or coin = 4 )) or
(dominant-survival? = 70 and ( coin = 1 or coin = 2 or coin = 3 )) or
(dominant-survival? = 80 and ( coin = 1 or coin = 2 )) or
(dominant-survival? = 90 and ( coin = 1 )) or
(dominant-survival? = 100 and ( coin = 0 )) [die]]
ask recessives [set coin one-of (list 1 2 3 4 5 6 7 8 9 10)
if ( recessive-survival? = 0 and ( coin != 0 )) or
(recessive-survival? = 10 and ( coin != 1 )) or
(recessive-survival? = 20 and ( coin != 1 and coin != 2 )) or
(recessive-survival? = 30 and ( coin != 1 and coin != 2 and coin != 3 )) or
(recessive-survival? = 40 and ( coin != 1 and coin != 2 and coin != 3 and coin != 4 )) or
(recessive-survival? = 50 and ( coin != 1 and coin != 2 and coin != 3 and coin != 4 and coin != 5 )) or
(recessive-survival? = 60 and ( coin = 1 or coin = 2 or coin = 3 or coin = 4 )) or
(recessive-survival? = 70 and ( coin = 1 or coin = 2 or coin = 3 )) or
(recessive-survival? = 80 and ( coin = 1 or coin = 2 )) or
(recessive-survival? = 90 and ( coin = 1 )) or
(recessive-survival? = 100 and ( coin = 0 )) [die]]]
if selectionvictims = "allgenotypes" [ask dominants [set coin one-of (list 1 2 3 4 5 6 7 8 9 10)
if ( dominant-survival? = 0 and ( coin != 0 )) or
(dominant-survival? = 10 and ( coin != 1 )) or
(dominant-survival? = 20 and ( coin != 1 and coin != 2 )) or
(dominant-survival? = 30 and ( coin != 1 and coin != 2 and coin != 3 )) or
(dominant-survival? = 40 and ( coin != 1 and coin != 2 and coin != 3 and coin != 4 )) or
(dominant-survival? = 50 and ( coin != 1 and coin != 2 and coin != 3 and coin != 4 and coin != 5 )) or
(dominant-survival? = 60 and ( coin = 1 or coin = 2 or coin = 3 or coin = 4 )) or
(dominant-survival? = 70 and ( coin = 1 or coin = 2 or coin = 3 )) or
(dominant-survival? = 80 and ( coin = 1 or coin = 2 )) or
(dominant-survival? = 90 and ( coin = 1 )) or
(dominant-survival? = 100 and ( coin = 0 )) [die]]
ask heterozygotes [set coin one-of (list 1 2 3 4 5 6 7 8 9 10)
if ( heterozygote-survival? = 0 and ( coin != 0 )) or
(heterozygote-survival? = 10 and ( coin != 1 )) or
(heterozygote-survival? = 20 and ( coin != 1 and coin != 2 )) or
(heterozygote-survival? = 30 and ( coin != 1 and coin != 2 and coin != 3 )) or
(heterozygote-survival? = 40 and ( coin != 1 and coin != 2 and coin != 3 and coin != 4 )) or
(heterozygote-survival? = 50 and ( coin != 1 and coin != 2 and coin != 3 and coin != 4 and coin != 5 )) or
(heterozygote-survival? = 60 and ( coin = 1 or coin = 2 or coin = 3 or coin = 4 )) or
(heterozygote-survival? = 70 and ( coin = 1 or coin = 2 or coin = 3 )) or
(heterozygote-survival? = 80 and ( coin = 1 or coin = 2 )) or
(heterozygote-survival? = 90 and ( coin = 1 )) or
(heterozygote-survival? = 100 and ( coin = 0 )) [die]]
ask recessives [set coin one-of (list 1 2 3 4 5 6 7 8 9 10)
if ( recessive-survival? = 0 and ( coin != 0 )) or
(recessive-survival? = 10 and ( coin != 1 )) or
(recessive-survival? = 20 and ( coin != 1 and coin != 2 )) or
(recessive-survival? = 30 and ( coin != 1 and coin != 2 and coin != 3 )) or
(recessive-survival? = 40 and ( coin != 1 and coin != 2 and coin != 3 and coin != 4 )) or
(recessive-survival? = 50 and ( coin != 1 and coin != 2 and coin != 3 and coin != 4 and coin != 5 )) or
(recessive-survival? = 60 and ( coin = 1 or coin = 2 or coin = 3 or coin = 4 )) or
(recessive-survival? = 70 and ( coin = 1 or coin = 2 or coin = 3 )) or
(recessive-survival? = 80 and ( coin = 1 or coin = 2 )) or
(recessive-survival? = 90 and ( coin = 1 )) or
(recessive-survival? = 100 and ( coin = 0 )) [die]]]
end
;;;;;
;; Genotype Graph
;;;;;
to update-plot ;; Keeps the graph of relative proportions of genotypes up-to-date
set-current-plot "Genotypes"
set-current-plot-pen "Dominant"
plot (((count dominants) / ((count turtles) + .1))* 100)
set-current-plot-pen "Heterozygote"
plot (((count heterozygotes) / ((count turtles) + .1))* 100)
set-current-plot-pen "Recessive"
plot (((count recessives) / ((count turtles) + .1))* 100)
end
@#$#@#$#@
GRAPHICS-WINDOW
339
10
752
444
16
16
12.212121212121213
1
10
1
1
1
0
1
1
1
-16
16
-16
16
0
0
1
ticks
CC-WINDOW
5
760
761
855
Command Center
0
BUTTON
7
11
70
44
NIL
setup
NIL
1
T
OBSERVER
NIL
NIL
NIL
NIL
BUTTON
70
11
133
44
NIL
go
T
1
T
OBSERVER
NIL
NIL
NIL
NIL
BUTTON
133
11
196
44
step
go
NIL
1
T
OBSERVER
NIL
NIL
NIL
NIL
SLIDER
8
88
180
121
#dominants
#dominants
0
10
0
1
1
NIL
HORIZONTAL
SLIDER
8
121
180
154
#heterozygotes
#heterozygotes
0
10
10
1
1
NIL
HORIZONTAL
SLIDER
8
154
180
187
#recessives
#recessives
0
10
0
1
1
NIL
HORIZONTAL
PLOT
81
497
447
647
Genotypes
NIL
NIL
0.0
10.0
0.0
10.0
true
false
PENS
"Dominant" 1.0 0 -13345367 true
"Heterozygote" 1.0 0 -10899396 true
"Recessive" 1.0 0 -1184463 true
MONITOR
81
648
176
693
Total # of Turtles
count dominants + count heterozygotes + count recessives
17
1
11
MONITOR
176
648
257
693
% Dominant
((count dominants) / \n((count turtles) + .1))\n* 100
0
1
11
MONITOR
257
648
362
693
% Heterozygote
((count heterozygotes) / \n((count turtles) + .1))\n* 100
0
1
11
MONITOR
362
648
447
693
% Recessive
((count recessives) / \n((count turtles) + .1))\n* 100
0
1
11
SWITCH
34
46
166
79
randomtraits?
randomtraits?
1
1
-1000
SWITCH
181
122
332
155
showasdifferent?
showasdifferent?
0
1
-1000
SLIDER
8
232
180
265
reproage
reproage
0
100
100
1
1
NIL
HORIZONTAL
BUTTON
8
279
97
312
NIL
bottleneck
NIL
1
T
OBSERVER
NIL
NIL
NIL
NIL
SWITCH
96
279
214
312
bylocation?
bylocation?
1
1
-1000
SLIDER
8
199
180
232
maxnumber
maxnumber
0
1000
1000
100
1
NIL
HORIZONTAL
MONITOR
175
693
258
746
# Dominants
count dominants
17
1
13
MONITOR
258
693
363
746
# Heterozygotes
count heterozygotes
17
1
13
MONITOR
363
693
447
746
# recessives
count recessives
17
1
13
BUTTON
8
311
97
356
NIL
select
NIL
1
T
OBSERVER
NIL
NIL
NIL
NIL
CHOOSER
96
311
214
356
selectionvictims
selectionvictims
"dominants" "heterozygotes" "recessives" "allbutdominants" "allbutheterozygotes" "allbutrecessives" "allgenotypes"
6
SLIDER
8
371
185
404
dominant-survival?
dominant-survival?
0
100
0
10
1
NIL
HORIZONTAL
SLIDER
8
404
185
437
heterozygote-survival?
heterozygote-survival?
0
100
0
10
1
NIL
HORIZONTAL
SLIDER
8
437
185
470
recessive-survival?
recessive-survival?
0
100
0
10
1
NIL
HORIZONTAL
@#$#@#$#@
WHAT IS IT?
-----------
Evolution can be defined as the changes in the genetic makeup of a population over time. This change can be both active and passive, being driven by either direct selection pressures or by random chance. The purpose of this model is to show the effects of both of these types of change in the form of a basic selection event and a bottleneck event, which represents sudden, random change. Ultimately, this model can show that random change can have effects on a population similar to the effects of selection and by extension that selection is instrumental but not essential to the course of evolution.
HOW IT WORKS
------------
Turtles are created with certain genotypes: homozygous dominant, heterozygous, or homozygous recessive. They move at random through the world, getting older at each tick. When two turtles that have reached their reproductive age land on the same patch, they produce a single offspring. The offspring have genotypes according to the genotypes of their parents and the rules of basic Mendelian genetics. The turtles, once they've reproduced, die out in proportion to their population size. The ratios of genotypes in the population are monitored on the graph.
The "bottleneck" and "select" features allow the user to suddenly reduce the population size according to either random chance or changeable selection parameters.
HOW TO USE IT
-------------
Begin by setting the randomtraits? switch to either "on" or "off". If the randomtraits? switch is set to "on", the model will create a random number of dominant (blue) turtles (0-10), heterozygous (blue/green) turtles (0-10) and recessive (yellow) turtles (0-10). If the randomtraits? switch is set to "off", select the number of each genotype to create using the appropriate sliders. If the "showasdifferent?" switch is on, the heterozygotes will display their own distinct phenotype (green color). If it is off, they will display the dominant phenotype (blue color). The "Setup" button will clear the world and create the desired turtles.
Using the "maxnumber" and "reproage" sliders, select the desired maximum population size and the age the turtles must be before they reproduce respectively.
Hit "Go" to run the model continuously, or "Step" to run it one iteration at a time.
To cause a bottleneck event, set the "bylocation?" switch to either "on" (to kill all turtles in Quadrants I, III and IV) or "off" (to kill 3/4 of the total population at random). Hitting the "bottleneck" button will cause the event to occur and will update the graph to reflect the sudden changes.
To see the effects of selection pressure on the population, a few parameters must be set. Begin by selecting the genotype against which you'd like to select. You can choose to select against any single genotype, any combination of two genotypes, or all three of the genotypes. The "[genotype]-survival?" sliders allow you to select the probability that each genotype will die if the "Select" button is hit. O indicates that all the turtles of the genotype will die every time (they will survive 0% of the time), 50 indicates that they have a 50/50 chance of dying each time (they will survive 50% of the time) and 100 indicates that they will survive 100% of the time. Hitting the "Select" button will kill off a number of turtles that is consistent with the survival parameters you've selected.
THINGS TO NOTICE
----------------
Watch the graph as it shows the changing ratios of genotypes in the population. Notice the overall trend in the ratios. Which genotype is most prevalent in the population? Which is least prevalent? What happens when a bottleneck event occurs? Are these changes permanent? If not, how long does it take before the original trend returns?
THINGS TO TRY
-------------
Begin by creating 10 dominant or 10 recessive turtles and running the program. Notice the effects of a bottleneck event and of selective pressure on a population without genetic variability. Next, create 10 heterozygous turtles and run the program. Notice the effects of bottlenecking and selection of a population with equal numbers of dominant and recessive alleles.
Try beginning with different ratios of genotypes, or let the random generator select the initial genotypes for you. Run the program and observe the effects of bottlenecking on the population until you are familiar with them. Then, begin with the same genotypic ratios and try to find the right combination of selective pressures to put upon the population to mimic the previously-observed effects of the bottleneck event.
CREDITS AND REFERENCES
----------------------
Thanks to Paul Grobstein and the students of the Spring 2009 Emergence course for their guidance and input into the concept of this model, and especially to Evan R for his help with the programming.
@#$#@#$#@
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Polygon -7500403 true true 25 114 16 195 9 204 23 213 25 200 39 123
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Circle -16777216 true false 180 75 60
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Circle -16777216 true false 60 75 60
Circle -16777216 true false 180 75 60
Polygon -16777216 true false 150 168 90 184 62 210 47 232 67 244 90 220 109 205 150 198 192 205 210 220 227 242 251 229 236 206 212 183
fish
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Polygon -7500403 true true 30 136 151 77 226 81 280 119 292 146 292 160 287 170 270 195 195 210 151 212 30 166
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flag
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Line -7500403 true 75 45 90 45
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Circle -7500403 true true 130 147 38
Circle -7500403 true true 192 85 38
Circle -7500403 true true 85 40 38
Circle -7500403 true true 177 40 38
Circle -7500403 true true 177 132 38
Circle -7500403 true true 70 85 38
Circle -7500403 true true 130 25 38
Circle -7500403 true true 96 51 108
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Polygon -10899396 true false 189 233 219 188 249 173 279 188 234 218
Polygon -10899396 true false 180 255 150 210 105 210 75 240 135 240
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Polygon -7500403 true true 105 90 60 150 75 180 135 105
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Circle -7500403 false true 24 174 42
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Line -7500403 true 40 84 269 221
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@#$#@#$#@
NetLogo 4.0.4
@#$#@#$#@
@#$#@#$#@
@#$#@#$#@
@#$#@#$#@
@#$#@#$#@
default
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Line -7500403 true 150 150 210 180
@#$#@#$#@