Sheep&CattleHerdDynamics

globals [
  CFR ;; quantity (kg) of fodder required by cattle herd from current step
  SFR ;; quantity (kg) of fodder required by sheep herd from current step
  CLR ;; area (ha) of land required by cattle herd from current step
  SLR ;; area (ha) of land required by sheep herd from current step
  LR ;; total pastureland (ha) required by both herds from current step
  LB ;; total labour (hrs) required to produce fodder required by both herds from current step
  LBL ;; list of LB values
  MC ;; manure (kg) collected from cattle herd from current step
  R ;; total number of steps per run of model
  AMP ;; average meat (kg) produced by cattle and sheep herd from previous 10 steps
  AMkP ;; average milk (l) produced by cattle and sheep herd from previous 10 steps
  AWP ;; average wool (kg) produced by sheep herd from previous 10 steps
  Cal ;; total calories (kcal) available from milk and meat produced from current step
  CPYC ;; number of cattle remaining at end of previous step
  CTYC ;; number of cattle remaining at end of current step
  SPYC ;; number of sheep remaining at end of previous step
  STYC ;; number of sheep remaining at end of current step
  CGR ;; population growth rate of cattle herd
  CGRL ;; list of CGR values
  CAGR ;; average growth rate of cattle herd per ten steps
  CMP ;; meat (kg) produced by cattle herd from current step
  CMPL ;; list of CMP values
  CMkP ;; milk (l) produced by cattle herd from current step
  CMkPL ;; list of CMkP values
  SGR ;; population growth rate of sheep herd
  SGRL ;; list of SGR values
  SAGR ;; average growth rate of sheep herd per ten steps
  SMP ;; meat (kg) produced by sheep herd from current step
  SMPL ;; list of SMP values
  SMkP ;; milk (l) produced by sheep herd from current step
  SMkPL ;; list of SMkP values
  SWP ;; wool (kg) produced by sheep herd from current step
  SWPL ;; list of SWP values
  CAM ;; number of dead adult cattle from current step
  CIM ;; number of dead immature cattle from current step
  CYM ;; number of dead young cattle from current step
  CNM ;; number of dead newborn cattle from current step
  SAM ;; number of dead adult sheep from current step
  SIM ;; number of dead immature sheep from current step
  SYM ;; number of dead young sheep from current step
  SNM ;; number of dead newborn sheep from current step
  MP ;; total meat (kg) produced by cattle and sheep herds from current step
  MkP ;; total milk (l) produced by cattle and sheep herds from current step
  MPL ;; list of MP values
  MkPL ;; list of Mk values
  C ;; number of ticks
  AWS ;; adult sheep weight
  AWC ;; adult cow weight
  IWS ;; immature sheep weight
  IWC ;; immature cow weight
  YWC ;; young cow weight
  YWS ;; young sheep weight
  SWY ;; annual sheep wool yield
  SMY ;; annual sheep milk yield
  CMY ;; annual cow milk yield
  catastrophe? ;; records whether a castrophic event has occured
  SLE ;; sheep life expectancy
  CLE ;; cow life expectancy
  NCM ;; newborn cattle mortality rate
  NSM ;; newborn sheep mortality rate
]
breed [ ;; creates the various breeds for the two types of animals based on age group
  adultcows adultcow
]
breed [
  immaturecows immaturecow
]
breed [
  youngcows youngcow
]
breed [
  newborncows newborncow
]
breed [
  adultsheeps adultsheep
]
breed [
  immaturesheeps immaturesheep
]
breed [
  youngsheeps youngsheep
]
breed [
  newbornsheeps newbornsheep
]
turtles-own [ ;; stores age of individual animal and whether or not the animal is lactating
  age
  lactating
]

to setup
  ca
  reset-ticks
  set C 0 ;; resets counter value to 0
  set LR 0 ;; resets land requirement to 0
  set R 100 ;; sets number of steps of the model to 100
  set catastrophe? "NO" ;; sets initial value for catastrophe? as no
  set CGRL ( n-values ( R + 1 ) [ 0 ] ) ;; following commands create the various list variables (see above), which comprises 100 empty items (one item per step therefore)
  set CMPL ( n-values R [ 0 ] )
  set CMkPL ( n-values ( R + 1 ) [ 0 ] )
  set SGRL ( n-values (R + 1) [ 0 ] )
  set SMPL ( n-values (R + 1)  [ 0 ] )
  set SMkPL ( n-values (R + 1)  [ 0 ] )
  set SWPL ( n-values (R + 1)  [ 0 ] )
  set MkPL ( n-values ( R + 1 ) [ 0 ] )
  set MPL ( n-values ( R + 1 ) [ 0 ] )
  set LBL ( n-values ( R + 1 ) [ 0 ] )
  set AWS 25 ;; sets weight of adult sheep as 25kg
  set AWC 200 ;; sets weight of adult cattle as 200kg
  set IWS 15 ;; sets weight of immature sheep as 15kg
  set IWC 75 ;; sets weight of immature cattle as 75kg
  set YWC 35 ;; sets weight of young cattle as 35kg
  set YWS 7.5 ;; sets weight of young sheep as 7.5kg
  set SWY 2 ;; sets annual yield of fleece from adult/immature sheep as 2kg
  set SMY 60 ;; sets annual milk yield of adult lactating sheep as 60l
  set CMY 150 ;; sets annual milk yield of adult lactating cattle as 150l
  set SLE 10 ;; sets maximum age of sheep as 10 years
  set CLE 20 ;; sets maximum age of cattle as 20 years
  set NCM 0.3 ;; sets newborn mortality rate of cattle as 30%
  set NSM 0.3 ;; sets newborn mortality rate of sheep as 30%
  create-adultcows 10 [ ;; following commands create turtles of various breeds and assigns a random age for each individual within the ranges assumed per animal species and age cohort
    set age 4 + random 16
  ]
  create-immaturecows 10 [
    set age one-of [ 1 2 3 ]
  ]
  create-youngcows 10 [
    set age 0
  ]
  create-adultsheeps 10 [
    set age 2 + random 8
  ]
  create-immaturesheeps 10 [
    set age 1
  ]
  create-youngsheeps 10 [
    set age 0
  ]
end 

to go
  if count turtles = 0 [ ;; model does not run if there are no turtles
    stop
  ]
  if ticks = R [ ;; model does not run if number of ticks exceeds the runtime (100 steps)
    stop
  ]
  set CPYC ( count adultcows + count immaturecows + count youngcows ) ;; sets the value for CPYC (count previous year cattle) as the current number of cattle
  set SPYC ( count adultsheeps + count immaturesheeps + count youngsheeps ) ;; sets the value for SPYC (count previous year sheep) as the current number of sheep
  set CAM 0 ;; following commands reset the number of animals that have died to 0 at the beginning of each step
  set CIM 0
  set CYM 0
  set SAM 0
  set SIM 0
  set SYM 0
  set CNM 0
  set SNM 0
  set MC 0 ;; resets the manure yield of cattle to 0 at the beginning of each step
  set Cal 0 ;; resets the number of calories yielded by the herds to 0 at the beginning of each step
  set CFR 0 ;; following commands reset the fodder requirement of sheep and cattle to 0 at the beginning of each step
  set SFR 0
  GoEpidemic
  GoAnimals
  GoFodder
  GoLand
  GoManure
  GoGrowthRate
  GoProduction
  GoCalories
  set C C + 1 ;; increases value for counter by 1 at end of each step
  tick
end 

to GoEpidemic
  if enable-catastrophe? = "TRUE"[ ;; following commands only called if value for enable-catastrophe switch is TRUE
    if catastrophe? = "NO" [ ;; following commands only called if value for global variable catastrophe? is NO, i.e. catastrophic event has not occured yet during model's run
      if count turtles with [ breed != newbornsheeps and breed != newborncows ] >= 50 [ ;; following commands only called if number of animals >= 50
        ask n-of ( count turtles * 0.9 ) turtles [ ;; kills 90% of all turtles
          die
        ]
        set catastrophe? "YES" ;; sets value for catastrophic event to "YES" to prevent further catastrophic events reoccuring during model's run
      ]
    ]
  ]
end 

to GoAnimals
  ask adultsheeps [ ;; following commands simulate reproduction by adult sheep of newborn sheep according to probability of birthing (i.e. value for SBa).
    set lactating "N"
    if random-float 1 < SBa [
      hatch 1 [
        set breed newbornsheeps
        set age 0
      ]
      set lactating "Y" ;; sets value for lactating of any adult sheep that has reproduced to "Y" i.e. yes
    ]
    if random-float 1 < sheep-adult-mortality [ ;; simulates death of adult sheep according to probability of occurence
      set SAM SAM + 1 ;; if adult sheep dies, value for SAM is increases by 1
      die
    ]
    set age age + 1 ;; if adult sheep survives, age is increased by 1
    if age > SLE [ ;; if age of adult sheep exceeds life expectancy, the animal is killed
      die
    ]
  ]
  ask adultcows [
    set lactating "N"
    if random-float 1 < CBa [ ;; simulates reproduction by adult cattle, process not different to that of sheep (see above)
      hatch 1 [
        set breed newborncows
        set age 0
      ]
      set lactating "Y"
    ]
    if random-float 100 / 100 < cow-adult-mortality [ ;; simulates death of adult cattle (see description of process affecting adult sheep above)
      set CAM CAM + 1
      die
    ]
    set age age + 1
    if age > CLE [
      die
    ]
  ]
  ask immaturesheeps [ ;; following commands simulate death of individual animals according to probabilities of mortality per species and per age cohort (see mortality processes of adult cattle and sheep above)
    if random-float 100 / 100 < sheep-immature-mortality [
      set SIM SIM + 1
      die
    ]
    set age age + 1
    set breed adultsheeps
  ]
  ask immaturecows [
    if random-float 100 / 100 < cow-immature-mortality [
      set CIM CIM + 1
      die
    ]
    set age age + 1
    if age = 4 [
      set breed adultcows
    ]
  ]
  ask youngsheeps [
    if random-float 100 / 100 < sheep-young-mortality [
      set SYM SYM + 1
      die
    ]
    set age age + 1
    set breed immaturesheeps
  ]
  ask youngcows [
    if random-float 100 / 100 < cow-young-mortality [
      set CYM CYM + 1
      die
    ]
    set age age + 1
    set breed immaturecows
  ]
  ask newbornsheeps [
    if random-float 100 / 100 < NSM [
      set SNM SNM + 1
      die
    ]
    set age age + 1
    set breed youngsheeps
  ]
  ask newborncows [
    if random-float 100 / 100 < NCM [
      set CNM CNM + 1
      die
    ]
    set age age + 1
    set breed youngcows
  ]
end 

to GoFodder ;; calculates fodder required (kg) by cattle and sheep herds
    set CFR ( count adultcows * ( 800 * ( AWC / 200 ) ) + count immaturecows * ( 800 * ( IWC / 200 ) ) + count youngcows * ( 800 * ( YWC / 200 ) ) ) ;; sets fodder required by cattle herd
    set SFR ( count adultsheeps * (306 * ( AWS / 30 ) ) + count immaturesheeps * ( 306 * ( IWS / 30 ) ) + count youngsheeps * ( 306 * ( YWS / 30 ) ) ) ;; sets fodder required by sheep herd
    set LB ( ( CFR + SFR ) / 3000 * 4 ) ;; sets labour in hours required to produce fodder
    set LBL replace-item C LBL LB ;; adds value calculated above to list LBL
end 

to GoLand ;; calculates pasture land required by cattle and sheep
  set SLR ( ( count adultsheeps + count immaturesheeps + ( count youngsheeps * ( 11 / 12 ) * 0.5 ) ) + ( SFR / 3000 ) ) / 7.5 ;; sets pasture land required by sheep herd
  set CLR ( ( count adultcows + count immaturecows + ( count youngcows * ( 7 / 12 ) * 0.5 ) ) ) * 8 / 12 + ( CFR / 3000 ) / 3 ;; sets pasture land required by cattle herd
  set LR ( SLR + CLR ) ;; sets value for total pastureland required
end 

to GoManure ;; calculates quantity of manure (kg) produced by cattle herd for four months during winter
  let manure-output-cow ( ( count adultcows * ( AWC * 0.075 ) ) + ( count immaturecows * ( IWC * 0.075 ) ) + ( count youngcows * ( YWC * 0.075 ) ) ) ;; calculates manure output per day of cattle herd
  set MC manure-output-cow * 240 ;; calculates manure output of cattle herd for total period of time manure available (four months during winter, plus nights for remainder of the year)
end 

to GoProduction
  set CMP ( CAM * ( AWC * 0.3 ) + CIM * ( IWC * 0.35 ) + CYM * ( YWC * 0.4 ) ) ;; calculates quantity of meat (kg) produced by cattle herd as number of dead animals adjusted for % of carcass edible
  set CMPL replace-item C CMPL CMP ;; updates list CMPL with value calculated above
  set CMkP ( ( count adultcows with [ lactating = "Y" ] ) * CMY ) ;; calculates quantity of milk (l) produced by cattle herd
  set CMkPL replace-item C CMkPL CMkP ;; updates list CMkPL with value calculate above
  set SMP ( SAM * ( AWS * 0.3 ) + SIM * ( IWS * 0.35 ) + SYM * ( YWS * 0.4 ) ) ;; calculates quantity of meat (kg) produced by shee[ herd as number of dead animals adjusted for % of carcass
  set SMPL replace-item C SMPL SMP ;; updates list CMPL with value calculated above
  set SMkP ( ( count adultsheeps with [ lactating = "Y" ] ) * SMY ) ;; calculates quantity of milk (l) produced by cattle herd
  set SMkPL replace-item C SMkPL SMkP ;; updates list CMPL with value calculated above
  set SWP ( ( count adultsheeps + count immaturesheeps ) * SWY );; calculates quantity of wool (kg) produced by sheep herd
  set SWPL replace-item C SWPL SWP ;; updates list CMPL with value calculated above
  set MP ( CMP + SMP ) ;; calculates total meat produced by both herds
  set MPL replace-item C MPL MP ;; updates list CMPL with value calculated above
  set MkP ( CMkP + SMkP )
  set MkPL replace-item C MkPL MkP ;; updates list CMPL with value calculated above
  if C > 9 [ ;; calculates average output of meat, milk and wool every ten steps
    set AMP mean  ( sublist MPL ( C - 9 ) ( C + 1 ) )
    set AMkP mean ( sublist MkPL ( C - 9 ) ( C + 1 ) )
    set AWP mean ( sublist SWPL ( C - 9) ( C + 1 ) )
    ]
end 

to GoGrowthRate ;; calculates % population growth rates of cattle and sheep herds
  set CTYC ( count adultcows + count immaturecows + count youngcows )
  if CTYC > 0 [
    set CGR ( 100 * ( CTYC - CPYC ) / CPYC )
    set CGRL replace-item C CGRL CGR
  ]
  if C > 8 [
    set CAGR mean ( sublist CGRL ( C - 9 ) ( C + 1 ) )
  ]
  set STYC ( count adultsheeps + count immaturesheeps + count youngsheeps )
  if STYC > 0 [
    set SGR ( 100 * ( STYC - SPYC ) / SPYC )
    set SGRL replace-item C SGRL SGR
  ]
  if C > 8 [
    set SAGR mean ( sublist SGRL ( C - 9 ) ( C + 1 ) )
  ]
end 

to GoCalories ;; calculates total calories supplied by milk and meat output of sheep and cattle herds
  set Cal ( (CMP * 0.6 * 1700 ) + ( CMP * 0.3 * 8000 ) + ( CMP * 2000 * 0.1 ) + ( SMP * 0.7 * 2930) + ( SMP * 0.2 * 6000 ) + ( SMP * 0.1 * 2000 ) )
end