# bears

Model was written in NetLogo 6.0.2
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globals [ max-sheep ] ; don't let sheep population grow too large ; Sheep and wolves are both breeds of turtle. breed [ sheep a-sheep ] ; sheep is its own plural, so we use "a-sheep" as the singular. breed [ wolves wolf ] breed [ bears bear ] turtles-own [ energy ] ; both wolves and sheep and bears have energy patches-own [ countdown ] to setup clear-all ifelse netlogo-web? [set max-sheep 10000] [set max-sheep 30000] ; Check model-version switch ; if we're not modeling grass, then the sheep don't need to eat to survive ; otherwise the grass's state of growth and growing logic need to be set up ifelse model-version = "sheep-wolves-grass" [ ask patches [ set pcolor one-of [ green brown ] ifelse pcolor = green [ set countdown grass-regrowth-time ] [ set countdown random grass-regrowth-time ] ; initialize grass regrowth clocks randomly for brown patches ] ] [ ask patches [ set pcolor white ] ] create-sheep initial-number-sheep ; create the sheep, then initialize their variables [ set shape "sheep" set color blue set size 1.5 ; easier to see set label-color blue - 2 set energy random (2 * sheep-gain-from-food) setxy random-xcor random-ycor ] create-wolves initial-number-wolves ; create the wolves, then initialize their variables [ set shape "wolf" set color orange set size 2 ; easier to see set energy random (2 * wolf-gain-from-food) setxy random-xcor random-ycor ] create-bears initial-number-bears ; create the wolves, then initialize their variables [ set shape "person" set color red set size 2.5 ; easier to see set energy random (2 * bear-gain-from-food) setxy random-xcor random-ycor ] display-labels reset-ticks end to go ; stop the simulation of no wolves or sheep if not any? turtles [ stop ] ; stop the model if there are no wolves and the number of sheep gets very large if not any? wolves and count sheep > max-sheep [ user-message "The sheep have inherited the earth" stop ] ask sheep [ move if model-version = "sheep-wolves-grass" [ ; in this version, sheep eat grass, grass grows and it costs sheep energy to move set energy energy - 1 ; deduct energy for sheep only if running sheep-wolf-grass model version eat-grass ; sheep eat grass only if running sheep-wolf-grass model version death ; sheep die from starvation only if running sheep-wolf-grass model version ] reproduce-sheep ; sheep reproduce at random rate governed by slider ] ask wolves [ move set energy energy - 1 ; wolves lose energy as they move eat-sheep ; wolves eat a sheep on their patch death ; wolves die if our of energy reproduce-wolves ; wolves reproduce at random rate governed by slider ] ask bears [ move set energy energy - 1 eat-wolves death reproduce-bears ] if model-version = "sheep-wolves-grass" [ ask patches [ grow-grass ] ] ; set grass count patches with [pcolor = green] tick display-labels end to move ; turtle procedure rt random 50 lt random 50 fd 1 end to eat-grass ; sheep procedure ; sheep eat grass, turn the patch brown if pcolor = green [ set pcolor brown set energy energy + sheep-gain-from-food ; sheep gain energy by eating ] end to eat-wolves let prey one-of sheep-here if prey != nobody [ ask prey [ die ] set energy energy + bear-gain-from-food ] end to reproduce-sheep ; sheep procedure if random-float 100 < sheep-reproduce [ ; throw "dice" to see if you will reproduce set energy (energy / 2) ; divide energy between parent and offspring hatch 1 [ rt random-float 360 fd 1 ] ; hatch an offspring and move it forward 1 step ] end to reproduce-wolves ; wolf procedure if random-float 100 < wolf-reproduce [ ; throw "dice" to see if you will reproduce set energy (energy / 2) ; divide energy between parent and offspring hatch 1 [ rt random-float 360 fd 1 ] ; hatch an offspring and move it forward 1 step ] end to eat-sheep ; wolf procedure let prey one-of sheep-here ; grab a random sheep if prey != nobody [ ; did we get one? if so, ask prey [ die ] ; kill it, and... set energy energy + wolf-gain-from-food ; get energy from eating ] end to reproduce-bears ; wolf procedure if random-float 100 < bears-reproduce [ ; throw "dice" to see if you will reproduce set energy (energy / 2) ; divide energy between parent and offspring hatch 1 [ rt random-float 360 fd 1 ] ; hatch an offspring and move it forward 1 step ] end to death ; turtle procedure (i.e. both wolf nd sheep procedure) ; when energy dips below zero, die if energy < 0 [ die ] end to grow-grass ; patch procedure ; countdown on brown patches: if reach 0, grow some grass if pcolor = brown [ ifelse countdown <= 0 [ set pcolor green set countdown grass-regrowth-time ] [ set countdown countdown - 1 ] ] end to-report grass ifelse model-version = "sheep-wolves-grass" [ report patches with [pcolor = green] ] [ report 0 ] end to display-labels ask turtles [ set label "" ] if show-energy? [ ask wolves [ set label round energy ] if model-version = "sheep-wolves-grass" [ ask sheep [ set label round energy ] ] ] end ; Copyright 1997 Uri Wilensky. ; See Info tab for full copyright and license.

There is only one version of this model, created about 3 years ago by nate wenzel.

## Attached files

File | Type | Description | Last updated | |
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bears.png | preview | Preview for 'bears' | about 3 years ago, by nate wenzel | Download |

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