Aggressiveness Sim

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WHAT IS IT?

This model aims to simulate the evolution, via natural selection, of aggressiveness in a population. It is very interesting to observe the success of these traits in a carefully managed population.

HOW IT WORKS

There are two types of turtles: aggressive turtles, which are red and shown by the red line on the graph, and nonaggressive turtles, which are blue and shown by the green line on the graph. Each turtle needs 2 food to survive, and another 2 food to reproduce (so 4 food total to survive AND reproduce). Intermediate amounts of food lead to corresponding chances of survival and reproduction. For example, 1 food will lead to a 50% chance of survival, while 2.5 food will lead to survival and a 25% chance of reproduction. Each cycle of the simulation, some randomly determined patches will grow 4 food. Each turtle will find a patch with food. If it is alone, it will eat all 4 food, thus reproducing. If it ends up on the same patch as a 2nd turtle, then if both turtles are nonaggressive, each turtle will get 2 food and survive; if both turtles are atggressive, each turtle will get somewhere between 0 and 1.5 food; and if there is one of each, the nonagressive one wil get between 0 and 1.5 food; the aggressive one will get between 2.5 and 4 food. If there are not enough patches with food for there to be no more than 2 turtles per patch, the extra turtles will automatically die.

HOW TO USE IT

First, one must setup the simulation:

• The percentAgrAtStart slider determines what percent of turtles will be aggressive when you click setup.
• the numStartingTurtles slider determines the amount of turtles that are created after you click setup.
• The worldWidth and worldHeight sliders control the width and height, respectively, of the world (in patches).
  • Note that world size does not affect the results of the simulation and is purely visual.

You are now ready to click setup and configure the simulation rules.

• The numFood slider determines the number of patches that will grow food each round.
  • The slightlyRandomFood? switch, when turned on, will allow for a random +/- 5 variation in the amount of patches that grow food each cycle, to create some variation between cycles.
• The agr-agrFood slider controls how much food each aggressive turtle gets when encountering another aggressive turtle.
• The agr-nonAgrFood slider controls how much food the aggressive turtle gets when encountering a nonaggressive turtle.
  • Note that the nonaggressive turtle will then get 4 - [whatever the slider is set to]
• The oldAge? switch, when turned on, will cause turtles to keep track of and die from old age.
  • The deathAge slider determines the age, in cycles, at which turtles will die.
  • The slightlyRandomDeath? switch, when turned on, will lead to +/- 3 random variation in a turtle's deathAge.
• The Add One Aggressive Turtle and the Add One Nonaggressive Turtle buttons can be pressed at any point while the simulation is running to insert one turtle of the respective type into the simulation.
• The whatTurtlesAlone? dropdown lets one choose which turtles, if any, prefer to be alone on a patch rather than sharing the patch with another turtle, when the amount of available patches permits this.
• The waitTime slider determines how long, in seconds, the feeding time lasts. This is purely visual and does not affect the results of the simulation. This slider also affects how long the turtles wiggle before going to a random food, also not affecting the results of the simulation. Setting this slider to 0 is perfect for running cycles very quickly, thus tracking the effects of various options over multiple generations in a short period of time.

THINGS TO NOTICE

Notice how at different combinations of simulation rules, the equilibrium that is achieved, as seen in the graph that shows the population of both aggressive and nonaggressive turtle, is different. This equilibrium can be determined algebraically by calculating and comparing the expected food values per cycle of each type of turtle; an equilibrium is achieved then these values are equal. Also notice how a population of all nonaggressive turtles will achieve a greater total population than a population of mixed turtles (or all aggressive turtles) under the same conditions, as can be seen on the total population graph. This shows how natural selection doesn't always lead to what is best for the species, but rather what is best for each trait. This can be tested by starting with wither all nonaggressive turtles or all aggressive turtles and then adding a couple of the opposite type of turtles using the buttons, and observing how that affects both realtive and total populations. Also note that it is easiest to spot patterns when waitTime is set to 0, since this allows the simulation to run cycles quicker.

THINGS TO TRY

We recommend starting at the following values for how much food turtles get, and playing around from there: agr-agrFood = 0, agr-nonAgr food = 3.

RELATED MODELS

Check out the models in the Social Science category of the models library: many of them explore or simualte similar principles to the ones shown in this simulation. More specifically: Altruism, Cooperation, and the models in the Prisoner's Dillema folder.

CREDITS AND REFERENCES

This model is mostly based on this video by Primer: https://youtu.be/YNMkADpvO4w?si=U0TPOxsYml1Sqmwo. Credit to this video for sparking my interest in behavioral simulations and the prisoner's dillema: https://youtu.be/mScpHTIi-kM?si=7q3HA5SyK_TxGaLV. Credits to the programs in the Model Library/Social Science/Prisoner's Dillema folder for helping inspire some functionality in this simulation.

There is only one version of this model, created 4 days ago by Samuel Sunko.

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