Predator Prey Grass 1

globals [ max-prey ]  ; don't let prey population grow too large
; Prey and predators are both breeds of turtle.
breed [ prey a-prey ]  ; prey is its own plural, so we use "a-prey" as the singular.
breed [ predators predator ]
turtles-own [ energy ]       ; both predators and prey have energy
patches-own [ countdown ]

to setup
  clear-all
  ifelse netlogo-web? [set max-prey 10000] [set max-prey 30000]

  ; Check model-version switch
  ; if we're not modeling grass, then the prey 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 = "predator-prey-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 green ]
  ]

  create-prey 100  ; create the prey, then initialize their variables
  [
    set shape  prey-type
    set color prey-color
    set size 1.5  ; easier to see
    set label-color blue - 2
    set energy random (2 * 4)
    setxy random-xcor random-ycor
  ]

  create-predators 100  ; create the predators, then initialize their variables
  [
    set shape predator-type
    set color predator-color
    set size 2  ; easier to see
    set energy random (2 * 20)
    setxy random-xcor random-ycor
  ]
  display-labels
  reset-ticks
end 

to go
  ; stop the simulation of no predators or prey
  if not any? turtles [ stop ]
  ; stop the model if there are no predators and the number of prey gets very large
  if not any? predators and count prey > max-prey [ user-message "The prey have inherited the earth" stop ]
  ask prey [
    move
    if model-version = "predator-prey-grass" [ ; in this version, prey eat grass, grass grows and it costs prey energy to move
      set energy energy - 1  ; deduct energy for prey only if running prey-predator-grass model version
      eat-grass  ; prey eat grass only if running prey-predator-grass model version
      death ; prey die from starvation only if running prey-predator-grass model version
    ]
    reproduce-prey  ; prey reproduce at random rate governed by slider
  ]
  ask predators [
    move
    set energy energy - 1  ; predators lose energy as they move
    eat-prey ; predators eat a prey on their patch
    death ; predators die if our of energy
    reproduce-predators ; predators reproduce at random rate governed by slider
  ]
  if model-version = "predator-prey-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  ; prey procedure
  ; prey eat grass, turn the patch brown
  if pcolor = green [
    set pcolor brown
    set energy energy + 4  ; prey gain energy by eating
  ]
end 

to reproduce-prey  ; prey procedure
  if random-float 100 < prey-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-predators  ; predator procedure
  if random-float 100 < predator-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-prey  ; predator procedure
  let food one-of prey-here                    ; grab a random prey
  if food != nobody  [                          ; did we get one?  if so,
    ask food [ die ]                            ; kill it, and...
    set energy energy + 20     ; get energy from eating
  ]
end 

to death  ; turtle procedure (i.e. both predator nd prey 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 = "predator-prey-grass" [
    report patches with [pcolor = green]
  ]
  [ report 0 ]
end 

to display-labels
  ask turtles [ set label "" ]
  if show-energy? [
    ask predators [ set label round energy ]
    if model-version = "predator-prey-grass" [ ask prey [ set label round energy ] ]
  ]
end 


; Copyright 1997 Uri Wilensky.
; See Info tab for full copyright and license.