Tuskless elephants

globals [ max-age circle-size]

turtles-own [ age gender tusk? ]

to setup
  ca

  set max-age 60 ;; agents can live up to max-age
  set circle-size 10 ;; bigger means smaller circles
  ask patches [ set pcolor brown + 4.9 ]

  crt total-population [


    ;; some initial values for every agent.

    set gender "male"
    set color red
    set shape "circle"
    set xcor random-xcor set ycor random-ycor
    set tusk? true
    set age random max-age
    set size age / circle-size ;; circle size grows with age.


    ;; initial gender distribution is 50%.
    ;; So we make half of the agents female.
    ;; Some of females are tuskless.

    if random 2 = 1
      [
        set gender "female"
        set color green
        if random 100 < ( initial-tusklessness * 2 ) [
          set tusk? false
          set color blue
        ]  ;; only females can be tuskless
      ]
  ]


  ;; check if we have any tuskless elephants

  if count turtles with [ tusk? = false ] < 1 and initial-tusklessness > 0
    [ setup ]

  reset-ticks
end 

to go
  ask turtles [
    ;; give birth in every 6 years after certain age
    if count turtles < max-allowed-population and gender = "female" and age > female-maturation-age and age mod 6 = 0 [

      ;; some default values
      let offspring-gender "male"
      let offspring-color red
      let offspring-tusk true

        if random 2 = 1      ;; initial gender distribution is 50%
          [
            set offspring-gender "female"
            set offspring-color green

            ;; if mother is tuskless, child's chance of being tuskless is 50%.
            ;; because father is tusky.

            if tusk? = false and random 2 = 1 [
              set offspring-tusk false
              set offspring-color blue
            ]
          ]

      ;; hello world
      hatch 1 [
        set age 1
        set xcor random-xcor set ycor random-ycor
        set tusk? offspring-tusk
        set gender offspring-gender
        set color offspring-color
        ] ;; /hatch
    ] ;; / if
  ] ;; / give birth


  ;; increase age and adjust size accordingly
  ask turtles [
    set age age + 1
    set size age / circle-size
  ]


  ;; grown ones will be hunted for tusks

  ask turtles [
    if tusk? and age >= tusk-maturation-age and ( random 100 <= kill-rate ) [ die ]
  ]


  ;; die naturally from old age

  ask turtles [
    if age > max-age [ die ]
  ]

  tick


  ;; stop execution. extinction case.
  if count turtles with [ gender = "male" ] = 0 or count turtles with [ gender = "female" ] = 0 [ stop ]
end 




;; Reset to initial values

to reset-to-defaults
  set initial-tusklessness 2
  set total-population 500
  set kill-rate 15
  set female-maturation-age 16
  set tusk-maturation-age 18
  set max-allowed-population 1000
end 




;; for plotting. checks against errors such as division by zero.

to-report mean-age-tusky
  ifelse count turtles with [ tusk? ] > 0 [
    report mean [ age ] of turtles with [ tusk? ]
  ]
  [ report 0 ]
end 

to-report mean-age-tuskless
  ifelse count turtles with [ tusk? = false ] > 0 [
    report mean [ age ] of turtles with [ tusk? = false ]
  ]
  [ report 0 ]
end 

to-report mean-age-females
  ifelse count turtles with [ gender = "female" ] > 0 [
    report mean [ age ] of turtles with [ gender = "female" ]
  ]
  [ report 0 ]
end 

to-report mean-age-males
  ifelse count turtles with [ gender = "male" ] > 0 [
    report mean [ age ] of turtles with [ gender = "male" ]
  ]
  [ report 0 ]
end 

to-report tusklessness-ratio
  ifelse count turtles with [ tusk? = false ] > 0 [
    report count turtles with [ tusk? = false ] / count turtles * 100
  ]
  [ report 0 ]
end 

to-report tusklessness-ratio-female-only
  ifelse count turtles with [ tusk? = false ] > 0 [
    report count turtles with [ tusk? = false ] / count turtles with [ gender = "female" ] * 100
  ]
  [ report 0 ]
end 

to-report count-tuskless
  ifelse count turtles with [ tusk? = false ] > 0 [
    report count turtles with [ tusk? = false ]
  ]
  [ report 0 ]
end 

to-report count-females
  ifelse count turtles with [ gender = "female" ] > 0 [
    report count turtles with [ gender = "female" ]
  ]
  [ report 0 ]
end 

to-report count-males
  ifelse count turtles with [ gender = "male" ] > 0 [
    report count turtles with [ gender = "male" ]
  ]
  [ report 0 ]
end