globals [ reproductionNoiseSD maxPop foodAvailable shares donations donationRate color-set turnInc maxDonationRate] turtles-own [tag tolerance skill age store] ;;;;;;;;;;;;;;;;;;;;;;; ;;; Setup procedure ;;; ;;;;;;;;;;;;;;;;;;;;;;; to setup clear-all set color-set [ red blue lime cyan yellow magenta gray orange violet ] set maxPop numFood / foodUsageRate set turnInc 360 / maxAge set maxDonationRate 1 ;; ??? do-attributes do-subpopulations do-profile reset-ticks end ;;;;;;;;;;;;;;;;; ;;; Main loop ;;; ;;;;;;;;;;;;;;;;; to go if ticks >= maxTime [ stop ] ;; if ticks = 0 [repeat initialPop [ generate-agent ]] ;; generate random newcomers repeat maxNumNew [ generate-agent ] ;; and any suitable existing agents reproduce ask turtles [ if (min store >= reproduceVal) [ hatch-agent tolerance tag skill set store map [ ? - initialFood ] store ] ] ;; scatter the food and share it out generate-food ask turtles [ let val (item skill store + item skill shares) if val > maxRes [ set val maxRes ] set store replace-item skill store val ] ;; then get agents to share where appropriate set donations 0 ask turtles [ do-sharing ] ifelse count turtles > 0 [ set donationRate donations / (numPairings * count turtles) ] [ set donationRate 0 ] ;; age, consume food and kill off any unfit agents ask turtles [ set age (age + 1) set store map [ ? - foodUsageRate ] store set size mean store if (min store <= 0) or (age > maxAge) [ die ] right turnInc ] ;; do displays do-attributes do-subpopulations do-profile tick end to basic-agent-settings set store (n-values numFoodTypes [initialFood]) set age 0 set size initialFood end to turtle-display-settings set heading 0 set size initialFood set color item skill color-set setxy tag * (world-width - 1) ((tolerance * (world-height - 1)) / maxTolerance) end ;; generate a random agent to generate-agent create-turtles 1 [ basic-agent-settings set skill (random numFoodTypes) set tolerance (random-float 1) * maxTolerance set tag random-float 1 turtle-display-settings ] end ;; create an offspring, given parent's tolerance, tag and skill to hatch-agent [Ptolerance Ptag Pskill] hatch 1 [ basic-agent-settings set skill Pskill set tolerance Ptolerance set tag Ptag if probValMutation > 0 [if random-float 1 < probValMutation [ set tolerance tolerance + random-normal 0 sdValMutation set tag tag + random-normal 0 sdValMutation ]] if sdReproductionNoise > 0 [ set tolerance tolerance + random-normal 0 sdReproductionNoise set tag tag + random-normal 0 sdReproductionNoise ] if tolerance < 0 [set tolerance 0] if tolerance > maxTolerance [set tolerance maxTolerance] if tag < 0 [set tag 0] if tag > 1 [set tag 1] if probSkillMutation > 0 [if random-float 1 < probSkillMutation [ set skill random numFoodTypes set color item skill color-set ]] turtle-display-settings ] end ;; maybe turtle display could be... plotted on a val/tolerance axis, with color being skill, ;; size being number at that val,tol and no direction? ;; scatter the food randomly amongst the food types ;; and calculate the share each agent should get to generate-food set foodAvailable (n-values numFoodTypes [0]) ;; why 100 here?? set foodAvailable map [? + random 100] foodAvailable let total sum foodAvailable ;; just in case 0 is randomly generated numFoodTypes times ;; (it did actually happen in testing!) ifelse total = 0 [ generate-food ] [ set foodAvailable map [ ? / total * numFood ] foodAvailable let pos 0 set shares [] repeat numFoodTypes [ let val count turtles with [ skill = pos ] ifelse val = 0 [set shares lput 0 shares] [set shares lput ((item pos foodAvailable) / val) shares] set pos pos + 1 ] ] end ;; agent tries random pairings to share any excess resources to do-sharing if count turtles > 1 [ ;; first determine excess let unneeded [] let pos 0 repeat numFoodTypes [ let val item pos store - excessVal ifelse val > 0 [set unneeded lput val unneeded] [set unneeded lput 0 unneeded] set pos pos + 1 ] ;; if agent has nothing to share, don't go further if sum unneeded = 0 [ stop ] ;; select numPairings partners, and keep the ones that ;; lie within tolerance let partners [] repeat numPairings [ let partner one-of other turtles let diff ([tag] of partner - tag) if diff < 0 [ set diff diff * -1 ] if diff < tolerance [set partners fput partner partners] ] ;; if there are any suitable partners, dole out the excess ;; and delete from own stores let num length partners if num > 0 [ set donations donations + 1 let j 0 repeat numFoodTypes [ let val item j store set store replace-item j store (val - item j unneeded) set j j + 1 ] set unneeded map [? / num] unneeded foreach partners [ ask ? [take-excess unneeded] ] ] ] end ;; incorporate donated resources into own stores to take-excess [ amounts ] let pos 0 repeat numFoodTypes [ let tmp item pos store + (item pos amounts) * donationBenefit if tmp > maxRes [ set tmp maxRes ] set store replace-item pos store tmp set pos pos + 1 ] end ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;; VISUALISATION PROCEDURES ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; to do-attributes set-current-plot "Agent Attributes" let num (count turtles) set-current-plot-pen "size" plot num / maxPop if num > 0 [ set-current-plot-pen "av. tolerance" plot (mean [tolerance] of turtles) / maxTolerance ] if count turtles > 0 [ set-current-plot-pen "donation rate" plot donationRate ] end to do-subpopulations set-current-plot "Subpopulations" set-plot-pen-mode 2 let pos 0 repeat numFoodTypes [ let current-set turtles with [skill = pos] set-plot-pen-color item pos color-set plot count current-set set pos pos + 1 ] end ;; plot each agent as a line representing its tag +/- tolerance ;; vertical axis is age, with agents evenly spaced between each ;; age point so that they can be more clearly seen to do-profile set-current-plot "Tag Profile" clear-plot set-plot-x-range 0 1 set-plot-y-range 0 maxAge let pos 0 repeat maxAge [ let current-set turtles with [age = pos] let num count current-set if num > 0 [ set current-set [self] of current-set let i 0 foreach current-set [ ask ? [ set-plot-pen-color color plot-pen-up plotxy (tag - tolerance) age + (i / num) plot-pen-down plotxy (tag + tolerance) age + (i / num) ] set i i + 1 ] ] set pos pos + 1 ] end @#$#@#$#@ GRAPHICS-WINDOW 455 362 750 678 -1 -1 6.97 1 10 1 1 1 0 0 0 1 0 40 0 40 0 0 1 ticks 30.0 BUTTON 718 10 784 43 NIL setup NIL 1 T OBSERVER NIL NIL NIL NIL 1 BUTTON 863 11 926 44 go go T 1 T OBSERVER NIL NIL NIL NIL 1 BUTTON 793 11 856 44 step go NIL 1 T OBSERVER NIL NIL NIL NIL 1 SLIDER 756 86 928 119 numFood numFood 0 500 500 1 1 NIL HORIZONTAL SLIDER 756 163 928 196 maxRes maxRes 0 10 7 0.1 1 NIL HORIZONTAL SLIDER 756 345 928 378 maxAge maxAge 0 100 20 1 1 NIL HORIZONTAL SLIDER 756 126 928 159 initialFood initialFood 0 10 1 1 1 NIL HORIZONTAL SLIDER 756 200 928 233 foodUsageRate foodUsageRate 0 1 0.25 0.01 1 NIL HORIZONTAL SLIDER 756 309 928 342 maxTolerance maxTolerance 0 1 0.1 0.01 1 NIL HORIZONTAL SLIDER 756 237 928 270 reproduceVal reproduceVal 0 10 4 0.5 1 NIL HORIZONTAL SLIDER 756 273 928 306 excessVal excessVal 0 10 5 0.5 1 NIL HORIZONTAL PLOT 301 10 712 356 Agent Attributes time proportion of max value 0.0 1000.0 0.0 1.0 true true "" "" PENS "size" 1.0 0 -2674135 true "" "" "av. tolerance" 1.0 0 -13345367 true "" "" "donation rate" 1.0 0 -10899396 true "" "" SLIDER 756 382 928 415 numFoodTypes numFoodTypes 0 9 3 1 1 NIL HORIZONTAL SLIDER 757 419 929 452 maxNumNew maxNumNew 0 10 2 1 1 NIL HORIZONTAL SLIDER 757 456 929 489 numPairings numPairings 0 20 6 1 1 NIL HORIZONTAL SLIDER 757 492 929 525 donationBenefit donationBenefit 0 1 0.9 0.01 1 NIL HORIZONTAL PLOT 9 11 292 355 Tag Profile Tag value Age 0.0 1.0 0.0 50.0 false false "" "" PENS "default" 1.0 0 -16777216 true "" "" SLIDER 757 529 929 562 sdValMutation sdValMutation 0 0.5 0.2 0.01 1 NIL HORIZONTAL SLIDER 758 565 930 598 probValMutation probValMutation 0 0.5 0.1 0.025 1 NIL HORIZONTAL SLIDER 757 48 929 81 maxTime maxTime 0 10000 10000 100 1 NIL HORIZONTAL SLIDER 758 639 930 672 sdReproductionNoise sdReproductionNoise 0 0.1 0.0032 0.0001 1 NIL HORIZONTAL PLOT 9 365 444 672 Subpopulations NIL NIL 0.0 10.0 0.0 10.0 true false "" "" PENS "default" 1.0 0 -16777216 true "" "" SLIDER 757 601 929 634 probSkillMutation probSkillMutation 0 0.2 0 0.01 1 NIL HORIZONTAL @#$#@#$#@ ## WHAT IS IT? This model demonstrates how cooperation (sharing) can be achieved through essentially selfish groups. Over time, groups of symbiotic relationships develop, and eventually collapse again. This is the model described in the paper: Edmonds, B. (2006) The Emergence of Symbiotic Groups Resulting From Skill-Differentiation and Tags. Journal of Artificial Societies and Social Simulation, 9(1). (http://jasss.soc.surrey.ac.uk/9/1/10.html). ## HOW IT WORKS Each agent can harvest food of a single type, but must have stores of all food types in order to survive. Agents with similar tag values will share excess resources, giving a means of accessing other resources. Agents who gather enough resources reproduce, propagting their strategies (with some mutation); agents who fail to gather sufficient resources die. ## HOW TO USE IT Press setup to initialise the model, then "step" for a single step, or "go" for continuous running. ## THINGS TO NOTICE Notice that setting maxNumNew to 0 is catastrophic - some random mutation of the population is essential. Once mutual donation has started occurring (when there are enough overlapping individuals of each food type) the population takes of and a "tag group" forms. Eventually this group fails, followed by a short period of non-viability before a new group forms. ## THE GRAPHS AND VISUALISATIONS The "Tag Profile" is a visualisation of all the individuals that are alive at this instance. Each individual is represented as a horizontal line, whose centre is at the individual's tag value and whose width is that of its tollerance. Given enough spare food each individual might donate some of its unneeded food to any other current individuals whose centre (i.e. tag) lies within its width. The bollour of the individual indicates its skill (i.e. the type of nutrition it can directly harvest). Clearly to be viable there must be some indivuals of each kind in each viablew tag group. The horizontal position of the lines indicate the age of the individual. Individuals of the same age are spread out a little horizontally so they can be seen. The "Agent Atributes" graph shows the population size, the avereage tollerance of individuals and the rate at which individuals donate to others. The "Subpopulations" graph shows the number of individuals of each skill type as a seperate line of dots (one colour for each type). Once a cooperative (i.e. mutally donating) tag group forms you see the population of all types rise and then oscilate with respect of each other until the group eventually collapses again to a situation of non-viability. The Turtle view is another visualisation of the current population. Each individual is represented by a seperate turtle their: x-position being their tag, y-position being their tolerance (up to the maximum value), their colour being their skill type, their size representing the average size of their stores, and the direction indicating their age (from veritcally upwards for age 0 and rotating to the right each time interval until almost vertical again at their maximum age). ## CREDITS AND REFERENCES The model was written by Bruce Edmonds and reimplemented in Java and Netlogo by Emma Norling. This model came out of many discussions with David Hales which started when we were trying to understand a model published as: Riolo, R. L., Cohen, M. D. and Axelrod, R. (2001) Evolution of cooperation without reciprocity. Nature, 411:441-443. Our analysis and critique of this model was: Edmonds, B. and Hales, D. (2003) Replication, Replication and Replication - Some Hard Lessons from Model Alignment. Journal of Artificial Societies and Social Simulation 6(4) (http://jasss.soc.surrey.ac.uk/6/4/11.html) This model is an attempt to produce a model of tag-based cooperation which did not suffer from the defects of the Riolo et al model, but showed genuiine tag-based cooperation. 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