File:Predator-prey toy model.gif

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    Summary

    Description
    English: An extremely simple predator-prey toy model. At each time step each pray (black dot) has a chance to duplicate, but is eaten if within a distance from predator (red circle). Predators can also duplicate, but have a chance to die, if they don't eat. To avoid the predator extinction one can either fine-tune the parameter, or build a more complex model.
    Date
    Source https://twitter.com/j_bertolotti/status/1424778017902039054
    Author Jacopo Bertolotti
    Permission
    (Reusing this file)
    https://twitter.com/j_bertolotti/status/1030470604418428929
    GIF development
    InfoField
     This diagram was created with Mathematica.

    Mathematica 12.0 code

    nprey = 2*10^3; npredator = 5; predatorradius = 0.3; stepprey = 0.2; steppredator = 0.2;
    prey0 = RandomReal[{-10, 10}, {nprey, 2}];
    predator0 = RandomReal[{-10, 10}, {npredator, 2}];
    prey = prey0; predator = predator0;
    probpreybreed = 0.025; probpredatordie = 0.2; probpredatorbreed = 0.2;
    histnprey = {}; histnpredator = {};
    evo = Reap[
        Do[
          feedingpredators = Table[0, npredator];
          For[j = 1, j <= npredator, j++,
           feeding = Position[Norm[# - predator[[j]]] & /@ prey, x_ /; (x < predatorradius)];
           prey = Delete[prey, feeding];
           If[Total[Flatten@feeding] > 0, feedingpredators[[j]] = 1];
            ];
          random = RandomReal[{0, 1}, npredator];
          dyingpredators = Position[random, x_ /; (x <= probpredatordie)];
          dyingpredators = DeleteCases[ Abs[(feedingpredators[[Flatten@dyingpredators]] - 1)*dyingpredators], {0}];
          predator = Delete[predator, dyingpredators];
          nprey = Dimensions[prey][[1]]; 
          npredator = Dimensions[predator][[1]];
          
          random = RandomReal[{0, 1}, npredator];
          breedingpredators = Flatten@Position[random, x_ /; (x <= probpredatorbreed)];
          predator = Join[predator, predator[[breedingpredators]] ];
          nprey = Dimensions[prey][[1]]; 
          npredator = Dimensions[predator][[1]];
          
          random = RandomReal[{0, 1}, nprey];
          breedingpreys = Flatten@Position[random, x_ /; (x <= probpreybreed)];
          prey = Join[prey, prey[[breedingpreys]] ];
          nprey = Dimensions[prey][[1]]; 
          npredator = Dimensions[predator][[1]];
          
          prey = Clip[prey + RandomVariate[NormalDistribution[0, stepprey], {nprey, 2}], {-10, 10}];
          predator = Clip[predator + RandomVariate[NormalDistribution[0, steppredator], {npredator, 2}], {-10, 
             10}];
          
          If[npredator < 1, Break[]];
          
          Sow[{prey, predator}]
          , {500}];
        ][[2]];
    
    history = Table[(Dimensions /@ evo[[1, k]] )[[All, 1]], {k, 1, Dimensions[evo[[1]] ][[1]]}];
    frames = Table[
       GraphicsRow[{
         Graphics[{Point[evo[[1, j, 1]]], Red, Thick, Circle[#, predatorradius] & /@ evo[[1, j, 2]] }, PlotRange -> {{-10, 10}, {-10, 10}}, ImageSize -> Large]
         ,
         GraphicsColumn[{
           ListLinePlot[history[[1 ;; j]], PlotRange -> {{0, Max@history[[All, 1]] + 100}, {-1, Max@history[[All, 2]] + 10}}, Axes -> False, Frame -> True, FrameLabel -> {"Prey", "Predators"}, LabelStyle -> {Black, Bold}, FrameTicks -> None, PlotStyle -> {Gray, Thick}, AspectRatio -> 1]
           ,
           ListLinePlot[history[[1 ;; j, 1]], PlotRange -> {{0, Dimensions[evo[[1]] ][[1]]}, {-1, Max@history[[All, 1]] + 10}}, Axes -> False, Frame -> True, FrameLabel -> {"Time", "Prey"}, LabelStyle -> {Orange, Bold}, FrameTicks -> None, PlotStyle -> {Orange, Thick}, AspectRatio -> 1]
           ,
           ListLinePlot[history[[1 ;; j, 2]], PlotRange -> {{0, Dimensions[evo[[1]] ][[1]]}, {-1, Max@history[[All, 2]] + 10}}, Axes -> False, Frame -> True, FrameLabel -> {"Time", "Predators"}, LabelStyle -> {Purple, Bold}, FrameTicks -> None, PlotStyle -> {Purple, Thick}, AspectRatio -> 1]
           }]
         }, ImageSize -> Large]
       , {j, 1, Dimensions[evo[[1]] ][[1]]}];
    ListAnimate[frames]
    

    Licensing

    I, the copyright holder of this work, hereby publish it under the following license:
    Creative Commons CC-Zero This file is made available under the Creative Commons CC0 1.0 Universal Public Domain Dedication.
    The person who associated a work with this deed has dedicated the work to the public domain by waiving all of their rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law. You can copy, modify, distribute and perform the work, even for commercial purposes, all without asking permission.

    Captions

    An extremely simple predator-prey toy model.

    Items portrayed in this file

    depicts

    9 August 2021

    image/gif

    6,658,669 byte

    489 pixel

    576 pixel

    3c534fff5d09ed74026fc8557fdba927d13707d6

    File history

    Click on a date/time to view the file as it appeared at that time.

    Date/TimeThumbnailDimensionsUserComment
    current16:10, 11 August 2021Thumbnail for version as of 16:10, 11 August 2021576 × 489 (6.35 MB)wikimediacommons>BertoUploaded own work with UploadWizard

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