Fish Predator Prey Interaction Model
Model was written in NetLogo 6.4.0
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globals [ patch-counter1 ;counter for setting patch color patch-counter2 ;counter for growing patches ] breed[prey a-prey] ;create prey breed breed[predators predator] ;create predator breed patches-own [ chl ;chl(mg/m^3) = Chlorophyl-A, a commonly used proxy for phytoplankton biomass ] turtles-own [ energy schoolmates ;agentset of nearby fish of the same species nearest-neighbor ;closest schoolmate targets ;agentset of potential targets for predators nearest-target ;closest target for predators attackers ;agentset of potential predators nearest-attacker ;closest predator to a prey fish attack-counter ;counter for whether a predator can attack or not ] to setup ca reset-ticks ask n-of food-clusters patches ;chl patch sizes are determined by the user [ ifelse food-cluster-size > 20 ;if food-cluster-size is set too small, it will cause an error when the radius is set to food-cluster-size/5 [ ask n-of food-cluster-size patches in-radius (food-cluster-size / 5) [ set chl 10 ] ] [ ask n-of food-cluster-size patches in-radius (food-cluster-size / 4) [ set chl 10 ] ] ] ask patches ;chl values are set in steps and are based upon the chl values of their neighbors, creating a realistic distribution of values [ if chl = 0 and [chl = 10] of one-of neighbors [ set chl 7 ] ] ask patches [ if chl = 0 and [chl >= 7] of one-of neighbors [ set chl 4 ] ] ask patches [ if chl = 0 and [chl >= 4] of one-of neighbors [ set chl 2 ] ] ask patches [ set pcolor scale-color green chl 18 0 set patch-counter1 25 set patch-counter2 bloom-time-interval if chl = 0 [ set pcolor sky ] ] create-prey initial-num-prey-fish ;initialize prey fish [ set size 3 set color orange setxy random-xcor random-ycor set schoolmates no-turtles set energy 299 ifelse fish? [set shape "fish"] [set shape "default"] ] create-predators initial-num-predator-fish ;initialize predator fish [ set size 5 set color red setxy random-xcor random-ycor set schoolmates no-turtles set energy 299 ifelse fish? [set shape "fish"] [set shape "default"] ] end to go ask patches [ set patch-counter1 patch-counter1 - 1 set patch-counter2 patch-counter2 - 1 if patch-counter2 <= 0 [ if chl <= 10 and [chl > 0] of one-of neighbors [ set chl chl + mean [chl] of neighbors ;creates a large chl (phytoplankton) bloom ] if chl > 10 [ set chl 10 ] set patch-counter2 bloom-time-interval ] if patch-counter1 <= 0 ;updates the map with new chl values [ set pcolor scale-color green chl 18 0 if chl >= 0 and chl < 0.4 [ set pcolor sky set chl 0 ] set patch-counter1 25 ] ] ask prey [ prey-move ] ask predators [ predator-move ] ask turtles [ forward 1 ] tick end to prey-move set schoolmates other prey in-radius vision set attackers other predators in-radius vision set energy energy - 0.2 if energy < 0 [ ask self [die] ] if energy > 300 ;energy needed to reproduce [ hatch 1 [ set schoolmates no-turtles set attackers no-turtles set energy 100 ] set energy energy - 100 ;reproduction cost ] ifelse random-float 1 < 0.08 ;random movement [ right (random 50) - 25 ] [ ifelse any? attackers [ set nearest-attacker min-one-of attackers [distance myself] turn-towards (atan [dx] of nearest-attacker [dy] of nearest-attacker) 30 ;prey evasive movement if vision > 0 [ forward vision / 3 ] ] [ if any? patches with [chl > 1] in-radius 3 ;prey eat phytoplankton [ let food max-one-of patches in-radius 3 [chl] turn-towards (towards food) prey-food-affinity set energy energy + (chl / 2) set chl chl / 2 ] if any? schoolmates [ set nearest-neighbor min-one-of schoolmates [distance myself] ifelse distance nearest-neighbor < 1 [ turn-away ([heading] of nearest-neighbor) 5 ;separates itself from neighbors if too close ] [ turn-towards average-schoolmate-heading 5 ;changes directions to align with neighbors headings to exhibit grouping behavior ] ] ] ] end to predator-move set schoolmates other predators in-radius vision set targets other prey in-radius vision set attack-counter attack-counter - 1 set energy energy - 0.6 if energy < 0 [ ask self [die] ] if energy > 300 ;energy needed to reproduce [ hatch 1 [ set schoolmates no-turtles set targets no-turtles set energy 100 ] set energy energy - 100 ;reproduction cost ] ifelse random-float 1 < 0.08 ;random movement [ right (random 50) - 25 ] [ ifelse any? targets [ set nearest-target min-one-of targets [distance myself] ifelse attack-counter <= 0 [ turn-away (atan [dx] of nearest-target [dy] of nearest-target) 30 ;predator attack movement if vision > 0 [ forward vision / 2 ] if random-float 1 < attack-success-rate ;attacks are successful half of the time [ ask nearest-target [die] set energy energy + 60 ] set attack-counter 15 ;predators will only attack after a given interval, creating a realistic attack pattern ] [ turn-away average-target-heading 20 ;predators will follow their targets ] ] [ if any? schoolmates ;if predators have no targets, they will school to hunt more efficiently [ set nearest-neighbor min-one-of schoolmates [distance myself] ifelse distance nearest-neighbor < 1 [ turn-away ([heading] of nearest-neighbor) 5 ;separates itself from neighbors if too close ] [ turn-towards average-schoolmate-heading 5 ] ] ] ] end ;Helper functions to turn-towards [new-heading max-turn-radius] ;turns towards something by subtracting current and new headings let turn subtract-headings new-heading heading ifelse abs turn > max-turn-radius [ ifelse turn > 0 [ right max-turn-radius ] [ left max-turn-radius ] ] [ ifelse turn > 0 [ right turn ] [ left turn ] ] end to turn-away [new-heading max-turn-radius] ;turns away from something by subtracting current and new headings let turn subtract-headings heading new-heading ifelse abs turn > max-turn-radius [ ifelse turn > 0 [ right max-turn-radius ] [ left max-turn-radius ] ] [ ifelse turn > 0 [ right turn ] [ left turn ] ] end to-report average-schoolmate-heading ;Cannot simply average heading values (ie. avg of 1 and 359 should be calculated as 0) let x-component sum [dx] of schoolmates let y-component sum [dy] of schoolmates ifelse x-component = 0 and y-component = 0 [ report heading ] [ report atan x-component y-component ] end to-report average-target-heading ;Cannot simply average heading values (ie. avg of 1 and 359 should be calculated as 0) let x-component sum [dx] of targets let y-component sum [dy] of targets ifelse x-component = 0 and y-component = 0 [ report heading ] [ report atan x-component y-component ] end
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