MIHS-18P2 caseyellakillian tortles coral garbage

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WHAT IS IT?

This model shows how damaging human trash is to sea turtles in the ocean.

HOW IT WORKS

There are two main variations to this model.

In the first variation, the "tortle-trash" version, trash and tortle wander randomly around the landscape, while the trash look for tortle to prey on. Each step costs the trash energy, and they must eat tortle in order to replenish their energy - when they run out of energy they die. To allow the population to continue, each wolf or tortle has a fixed probability of reproducing at each time step. In this variation, we model the coral as "infinite" so that tortle always have enough to eat, and we don't explicitly model the eating or growing of coral. As such, tortle don't either gain or lose energy by eating or moving. This variation produces interesting population dynamics, but is ultimately unstable. This variation of the model is particularly well-suited to interacting species in a rich nutrient environment, such as two strains of bacteria in a petri dish (Gause, 1934).

The second variation, the "tortle-trash-coral" version explictly models coral (green) in addition to trash and tortle. The behavior of the trash is identical to the first variation, however this time the tortle must eat coral in order to maintain their energy - when they run out of energy they die. Once coral is eaten it will only regrow after a fixed amount of time. This variation is more complex than the first, but it is generally stable. It is a closer match to the classic Lotka Volterra population oscillation models. The classic LV models though assume the populations can take on real values, but in small populations these models underestimate extinctions and agent-based models such as the ones here, provide more realistic results. (See Wilensky & Rand, 2015; chapter 4).

The construction of this model is described in two papers by Wilensky & Reisman (1998; 2006) referenced below.

HOW TO USE IT

Set the model-version chooser to "tortle-trash-coral" to include coral eating and growth in the model, or to "tortle-trash" to only include trash (black) and tortle (white).
Adjust the slider parameters (see below), or use the default settings.
Press the SETUP button.
Press the GO button to begin the simulation.
Look at the monitors to see the current population sizes
Look at the POPULATIONS plot to watch the populations fluctuate over time

Parameters: MODEL-VERSION: Whether we model tortle trash and coral or just tortle and trash INITIAL-NUMBER-tortle: The initial size of tortle population INITIAL-NUMBER-trash: The initial size of wolf population tortle-GAIN-FROM-FOOD: The amount of energy tortle get for every coral patch eaten (Note this is not used in the tortle-trash model version) WOLF-GAIN-FROM-FOOD: The amount of energy trash get for every tortle eaten tortle-REPRODUCE: The probability of a tortle reproducing at each time step WOLF-REPRODUCE: The probability of a wolf reproducing at each time step coral-REGROWTH-TIME: How long it takes for coral to regrow once it is eaten (Note this is not used in the tortle-trash model version) SHOW-ENERGY?: Whether or not to show the energy of each animal as a number

Notes: - one unit of energy is deducted for every step a wolf takes - when running the tortle-trash-coral model version, one unit of energy is deducted for every step a tortle takes

There are three monitors to show the populations of the trash, tortle and coral and a populations plot to display the population values over time.

If there are no trash left and too many tortle, the model run stops.

THINGS TO NOTICE

When running the tortle-trash model variation, watch as the tortle and wolf populations fluctuate. Notice that increases and decreases in the sizes of each population are related. In what way are they related? What eventually happens?

In the tortle-trash-coral model variation, notice the green line added to the population plot representing fluctuations in the amount of coral. How do the sizes of the three populations appear to relate now? What is the explanation for this?

Why do you suppose that some variations of the model might be stable while others are not?

THINGS TO TRY

Try adjusting the parameters under various settings. How sensitive is the stability of the model to the particular parameters?

Can you find any parameters that generate a stable ecosystem in the tortle-trash model variation?

Try running the tortle-trash-coral model variation, but setting INITIAL-NUMBER-trash to 0. This gives a stable ecosystem with only tortle and coral. Why might this be stable while the variation with only tortle and trash is not?

Notice that under stable settings, the populations tend to fluctuate at a predictable pace. Can you find any parameters that will speed this up or slow it down?

EXTENDING THE MODEL

There are a number ways to alter the model so that it will be stable with only trash and tortle (no coral). Some will require new elements to be coded in or existing behaviors to be changed. Can you develop such a version?

Try changing the reproduction rules -- for example, what would happen if reproduction depended on energy rather than being determined by a fixed probability?

Can you modify the model so the tortle will flock?

Can you modify the model so that trash actively chase tortle?

NETLOGO FEATURES

Note the use of breeds to model two different kinds of "turtles": trash and tortle. Note the use of patches to model coral.

Note use of the ONE-OF agentset reporter to select a random tortle to be eaten by a wolf.

RELATED MODELS

Look at Rabbits coral Weeds for another model of interacting populations with different rules.

CREDITS AND REFERENCES

Wilensky, U. & Reisman, K. (1998). Connected Science: Learning Biology through Constructing and Testing Computational Theories -- an Embodied Modeling Approach. International Journal of Complex Systems, M. 234, pp. 1 - 12. (The Wolf-tortle-Predation model is a slightly extended version of the model described in the paper.)

Wilensky, U. & Reisman, K. (2006). Thinking like a Wolf, a tortle or a Firefly: Learning Biology through Constructing and Testing Computational Theories -- an Embodied Modeling Approach. Cognition & Instruction, 24(2), pp. 171-209. http://ccl.northwestern.edu/papers/wolftortle.pdf .

Wilensky, U., & Rand, W. (2015). An introduction to agent-based modeling: Modeling natural, social and engineered complex systems with NetLogo. Cambridge, MA: MIT Press.

Lotka, A. J. (1925). Elements of physical biology. New York: Dover.

Volterra, V. (1926, October 16). Fluctuations in the abundance of a species considered mathematically. Nature, 118, 558–560.

Gause, G. F. (1934). The struggle for existence. Baltimore: Williams & Wilkins.

HOW TO CITE

If you mention this model or the NetLogo software in a publication, we ask that you include the citations below.

For the model itself:

Wilensky, U. (1997). NetLogo Wolf tortle Predation model. http://ccl.northwestern.edu/netlogo/models/WolftortlePredation. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.

Please cite the NetLogo software as:

Wilensky, U. (1999). NetLogo. http://ccl.northwestern.edu/netlogo/. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.

COPYRIGHT AND LICENSE

CC BY-NC-SA 3.0

This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License. To view a copy of this license, visit https://creativecommons.org/licenses/by-nc-sa/3.0/ or send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.

Commercial licenses are also available. To inquire about commercial licenses, please contact Uri Wilensky at uri@northwestern.edu.

This model was created as part of the project: CONNECTED MATHEMATICS: MAKING SENSE OF COMPLEX PHENOMENA THROUGH BUILDING OBJECT-BASED PARALLEL MODELS (OBPML). The project gratefully acknowledges the support of the National Science Foundation (Applications of Advanced Technologies Program) -- grant numbers RED #9552950 and REC #9632612.

This model was converted to NetLogo as part of the projects: PARTICIPATORY SIMULATIONS: NETWORK-BASED DESIGN FOR SYSTEMS LEARNING IN CLASSROOMS and/or INTEGRATED SIMULATION AND MODELING ENVIRONMENT. The project gratefully acknowledges the support of the National Science Foundation (REPP & ROLE programs) -- grant numbers REC #9814682 and REC-0126227. Converted from StarLogoT to NetLogo, 2000.

Comments and Questions

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Click to Run Model

globals [ max-tortles ]  ; don't let tortle population grow too large
; tortle and trash are both breeds of turtle.
breed [ tortles tortle ]  ; tortle is its own plural, so we use "a-tortle" as the singular.
breed [ trash a-trash ]
turtles-own [ energy ]       ; both trash and tortle have energy
patches-own [ countdown ]

to setup
  clear-all
  ifelse netlogo-web? [set max-tortles 10000] [set max-tortles 30000]

  ; Check model-version switch
  ; if we're not modeling coral, then the tortle don't need to eat to survive
  ; otherwise the coral's state of growth and growing logic need to be set up
  ifelse model-version = "tortles-trash-coral" [
    ask patches [
      set pcolor one-of [ pink blue ]
      ifelse pcolor = blue
        [ set countdown coral-regrowth-time ]
      [ set countdown random coral-regrowth-time ] ; initialize coral regrowth clocks randomly for blue patches
    ]
  ]
  [
    ask patches [ set pcolor pink ]
  ]

  create-tortles initial-number-tortles  ; create the tortle, then initialize their variables
  [
    set shape  "turtle"
    set color 52
    set size 5  ; easier to see
    set label-color blue - 2
    set energy random (2 * tortles-gain-from-food)
    setxy random-xcor random-ycor
  ]

  create-trash initial-number-trash  ; create the trash, then initialize their variables
  [
    set shape "garbage can"
    set color gray
    set size 4  ; easier to see
    set energy random (2 * trash-gain-from-food)
    setxy random-xcor random-ycor
  ]
  display-labels
  reset-ticks
end 

to go
  ; stop the simulation of no trash or tortle
  if not any? turtles [ stop ]
  ; stop the model if there are no trash and the number of tortle gets very large
  if not any? trash and count tortles > max-tortles [ user-message "The tortle have inherited the earth" stop ]
  ask tortles [
    move
    if model-version = "tortles-trash-coral" [ ; in this version, tortle eat coral, coral grows and it costs tortle energy to move
      set energy energy - 1  ; deduct energy for tortle only if running tortle-trash-coral model version
      eat-coral  ; tortle eat coral only if running tortle-trash-coral model version
      death ; tortle die from starvation only if running tortle-trash-coral model version
    ]
    reproduce-tortles  ; tortle reproduce at random rate governed by slider
  ]
  ask trash [
    move
    set energy energy - 1  ; trash lose energy as they move
    eat-tortles ; trash eat a tortle on their patch

  ]
  if not any? tortles [ user-message "congrats you killed them all. https://www.seeturtles.org/billion-baby-turtles-donations/" stop ]
  if model-version = "tortles-trash-coral" [ ask patches [ grow-coral ] ]
  ; set coral count patches with [pcolor = pink]
  tick
  display-labels
end 

to move  ; turtle procedure
  rt random 50
  lt random 50
  fd 1
end 

to eat-coral  ; tortle procedure
  ; tortle eat coral, turn the patch blue
  if pcolor = pink [
    set pcolor blue
    set energy energy + tortles-gain-from-food  ; tortle gain energy by eating
  ]
end 

to reproduce-tortles  ; tortle procedure
  if random-float 100 < tortles-reproduce [  ; throw "dice" to see if you will reproduce
    set energy (energy / 2)                ; divide energy between parent and offspring
    hatch 1 [ rt random-float 360 fd 1 ]   ; hatch an offspring and move it forward 1 step
  ]
end 

to reproduce-trash  ; trash procedure
  if random-float 100 < trash-reproduce [  ; throw "dice" to see if you will reproduce
    set energy (energy / 2)               ; divide energy between parent and offspring
    hatch 1 [ rt random-float 360 fd 1 ]  ; hatch an offspring and move it forward 1 step
  ]
end 

to eat-tortles  ; trash procedure
  let prey one-of tortles-here                    ; grab a random tortle
  if prey != nobody  [                          ; did we get one?  if so,
    ask prey [ die ]                            ; kill it, and...
    set energy energy + trash-gain-from-food     ; get energy from eating
  ]
end 

to death  ; turtle procedure (i.e. both trash nd tortle procedure)
  ; when energy dips below zero, die
  if energy < 0 [ die ]
end 

to grow-coral  ; patch procedure
  ; countdown on blue patches: if reach 0, grow some coral
  if pcolor = blue [
    ifelse countdown <= 0
      [ set pcolor pink
        set countdown coral-regrowth-time ]
      [ set countdown countdown - 1 ]
  ]
end 

to-report coral
  ifelse model-version = "tortles-trash-coral" [
    report patches with [pcolor = pink]
  ]
  [ report 0 ]
end 

to display-labels
  ask turtles [ set label "" ]
  if show-energy? [
    ask trash [ set label round energy ]
    if model-version = "tortle-trash-coral" [ ask tortles [ set label round energy ] ]
  ]
end 


; Copyright 1997 Uri Wilensky.
; See Info tab for full copyright and license.

There are 2 versions of this model.

		Uploaded by	When	Description	Download
		casey ella killian hh	over 6 years ago	we fixed it	Download this version
		casey ella killian hh	over 6 years ago	Initial upload	Download this version

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