;--------------------------------------------------- ;----- Create Agents ------------------------------- ;--------------------------------------------------- breed [rabbits rabbit] rabbits-own [ energy ] ;--------------------------------------------------- ;----- Setup --------------------------------------- ;--------------------------------------------------- ; Observer Procedure to setup clear-all ask patches [grow-grass] set-default-shape rabbits "rabbit" create-rabbits initial-num-rabbits [ set color white setxy random-xcor random-ycor set energy random 10 ;start with a random amt. of energy ] reset-ticks end ;--------------------------------------------------- ;----- Go ------------------------------------------ ;--------------------------------------------------- ; Observer Procedure to go if not any? rabbits [ stop ] ask patches [grow-grass] ask rabbits [ move eat-grass reproduce death ] tick end ;--------------------------------------------------- ;----- Grow Grass ---------------------------------- ;--------------------------------------------------- ; Patch Procedure to grow-grass if (pcolor = black) and (random-float 1 < grass-grow-rate) [ set pcolor green ] end ;--------------------------------------------------- ;----- Move ---------------------------------------- ;--------------------------------------------------- ; Rabbit Procedure to move set heading heading + (random-float 100 - 50) fd 1 set energy energy - 0.5 ;; moving takes some energy end ;--------------------------------------------------- ;----- Eat Grass ----------------------------------- ;--------------------------------------------------- ; Rabbit Procedure to eat-grass ;; gain energy by eating grass if pcolor = green [ set pcolor black set energy energy + grass-energy ] end ;--------------------------------------------------- ;----- Reproduce ----------------------------------- ;--------------------------------------------------- ; Rabbit Procedure to reproduce ;; rabbit procedure ;; give birth to a new rabbit, but it takes lots of energy if energy > birth-threshold [ set energy (energy / 2) hatch 1 [ fd 1 ] ] end ;--------------------------------------------------- ;----- Death --------------------------------------- ;--------------------------------------------------- ; Rabbit Procedure to death ;; die if you run out of energy if energy < 0 [ die ] end @#$#@#$#@ GRAPHICS-WINDOW 215 10 717 533 20 20 12.0 1 10 1 1 1 0 1 1 1 -20 20 -20 20 1 1 1 ticks 30.0 BUTTON 39 385 94 418 setup setup NIL 1 T OBSERVER NIL NIL NIL NIL 1 BUTTON 104 385 159 418 go go T 1 T OBSERVER NIL NIL NIL NIL 1 SLIDER 10 279 200 312 grass-grow-rate grass-grow-rate 0.0 0.05 0.026 0.001 1 NIL HORIZONTAL SLIDER 8 194 202 227 grass-energy grass-energy 0.0 10.0 5 0.5 1 NIL HORIZONTAL SLIDER 10 32 205 65 initial-num-rabbits initial-num-rabbits 0.0 500.0 150 1.0 1 NIL HORIZONTAL SLIDER 10 111 204 144 birth-threshold birth-threshold 0.0 20.0 5 1.0 1 NIL HORIZONTAL PLOT 728 10 1228 206 Populations Time Pop 0.0 100.0 0.0 111.0 true true "set-plot-y-range 0 initial-num-rabbits" "" PENS "grass" 1.0 0 -10899396 true "" "plot count patches with [pcolor = green]" "rabbits" 1.0 0 -12895429 true "" "plot count rabbits" MONITOR 1177 66 1266 111 count rabbits count rabbits 1 1 11 TEXTBOX 14 13 209 31 Set the initial number of rabbits: 11 0.0 1 TEXTBOX 13 79 217 107 Set the minimum amount of energy required for a rabbit to reproduce: 11 0.0 1 TEXTBOX 10 160 202 193 Set the amount of energy contained in each patch of grass: 11 0.0 1 TEXTBOX 13 246 206 274 Set the growth rate at which new patches of grass appear: 11 0.0 1 TEXTBOX 10 316 205 365 Example: A value of 0.015 means that at each time step each patch that does not currently contain a patch of grass has a 1.5% chance of growing a patch of grass. 9 3.0 1 BUTTON 58 442 137 475 MovieGo setup\nmovie-start \"Rabbits.mov\"\nrepeat 100\n[ go\n movie-grab-view ]\nmovie-close NIL 1 T OBSERVER NIL NIL NIL NIL 1 @#$#@#$#@ # Purpose This agent-based model explores a simple ecosystem made up of rabbits and grass. The rabbits wander around randomly, and the grass grows randomly. When a rabbit bumps into a patch of grass, it eats the grass and gains energy. If the rabbit gains enough energy, it reproduces. Each rabbit loses energy every time it moves and reproduces. If a rabbits loses too much energy it dies. # Entities and Variables ## Entities and their State Variables There are two entities in this model: rabbits (agents), and patches. Each rabbit has variables for their location, heading, and energy level. Each patch has a color variable which indicates if it contains grass or not. ## Global Parameters All of the global variables are set by the user in the interface. * `initial-num-rabbits` is the number of rabbits which initial appear in the ABM "world". * `birth-threshold` is the minimum amount of energy required for a rabbit to reproduce. * `grass-energy` is the amount of energy a single patch of grass contains. * `grass-grow-rate` gives the probability that a single patch which currently does not contain grass will produce grass in a single time step. # Process Overview After the model is initialized (see Initialization section for details), a simulation will run until there are no rabbits left or until the user stops the simulation. During each time step, the following events occur in the order they are listed: * If there are no rabbits left the simulation stops * Each patch executes the Grow Grass procedure (see Submodels section for details) * Each rabbit excutes the following procedures: Move > Eat Grass > Reproduce > Death * The time step is incremented by 1 ## Submodels ### Grow Grass ![Patch Context](http://ccl.northwestern.edu/netlogo/docs/images/patch.gif) If the patch is currently colored black (no grass), then with a probability of `grass-growth-rate` the patch will be colored green (contain grass). Note, to select when to color a patch green based on the probability `grass-growth-rate`, a random floating point value (real number) between 0 and 1 is generated. If that value is less than `grass-growth-rate`, then the patch is colored green, otherwise it remains black. ### Move ![Turtle Context](http://ccl.northwestern.edu/netlogo/docs/images/turtle.gif) The rabbit sets is current heading to a randomly selected heading within 50 degress (left or right). ### Eat Grass ![Turtle Context](http://ccl.northwestern.edu/netlogo/docs/images/turtle.gif) If the patch the rabbit currently occupies is green (has grass), then the rabbit will eat the grass. In doing so that patch color is turned to black (no more grass), and the rabbit's energy variable increases by the amount of `grass-energy`. ### Reproduce ![Turtle Context](http://ccl.northwestern.edu/netlogo/docs/images/turtle.gif) If the rabbit's energy variable is greater than the value of `birth-threshold`, then the rabbit will reproduce. In do so, the rabbit loses half of its energy. The offspring is place one patch length away from its parent in the direction of the parent's current heading. ### Death ![Turtle Context](http://ccl.northwestern.edu/netlogo/docs/images/turtle.gif) If the rabbit's energy variable is less than 0, then the rabbit dies. # How to Run a Simulation 1. Set each of the global variables at the desired values. 2. Click on the SETUP button to initialize the simulation: `initial-num-rabbits` will be place randomly across the model world, and be given a random initial energy (integer) value in the range [0,9]. The model world starts with no grass (all patches black), but during the setup procedure creates patches of grass according to the Grow Grass submodel. 3. Click on the GO button to start the simulation. # ... @#$#@#$#@ default true 0 Polygon -7500403 true true 150 5 40 250 150 205 260 250 airplane true 0 Polygon -7500403 true true 150 0 135 15 120 60 120 105 15 165 15 195 120 180 135 240 105 270 120 285 150 270 180 285 210 270 165 240 180 180 285 195 285 165 180 105 180 60 165 15 arrow true 0 Polygon -7500403 true true 150 0 0 150 105 150 105 293 195 293 195 150 300 150 box false 0 Polygon -7500403 true true 150 285 285 225 285 75 150 135 Polygon -7500403 true true 150 135 15 75 150 15 285 75 Polygon -7500403 true true 15 75 15 225 150 285 150 135 Line -16777216 false 150 285 150 135 Line -16777216 false 150 135 15 75 Line -16777216 false 150 135 285 75 bug true 0 Circle -7500403 true true 96 182 108 Circle -7500403 true true 110 127 80 Circle -7500403 true true 110 75 80 Line -7500403 true 150 100 80 30 Line -7500403 true 150 100 220 30 butterfly true 0 Polygon -7500403 true true 150 165 209 199 225 225 225 255 195 270 165 255 150 240 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0 150 150 pentagon false 0 Polygon -7500403 true true 150 15 15 120 60 285 240 285 285 120 person false 0 Circle -7500403 true true 110 5 80 Polygon -7500403 true true 105 90 120 195 90 285 105 300 135 300 150 225 165 300 195 300 210 285 180 195 195 90 Rectangle -7500403 true true 127 79 172 94 Polygon -7500403 true true 195 90 240 150 225 180 165 105 Polygon -7500403 true true 105 90 60 150 75 180 135 105 plant false 0 Rectangle -7500403 true true 135 90 165 300 Polygon -7500403 true true 135 255 90 210 45 195 75 255 135 285 Polygon -7500403 true true 165 255 210 210 255 195 225 255 165 285 Polygon -7500403 true true 135 180 90 135 45 120 75 180 135 210 Polygon -7500403 true true 165 180 165 210 225 180 255 120 210 135 Polygon -7500403 true true 135 105 90 60 45 45 75 105 135 135 Polygon -7500403 true true 165 105 165 135 225 105 255 45 210 60 Polygon -7500403 true true 135 90 120 45 150 15 180 45 165 90 rabbit false 0 Circle -7500403 true true 76 150 148 Polygon -7500403 true true 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