Blog Post

Bruce Lewis Final Project



A Netlogo Model:  
The Value of Hunting Seasons Toward the Equilibrium
Between the Overpopulation and Extinction of Wildlife

by Bruce Lewis

 UNM  CS 590 Course:
“Learning and Teaching Computer Science for All”



Table of Contents

1.       Introduction

2.       The Problem

3.       Equilibrium Model

4.       The Results Collected

5.       Conclusion

6.       References


Introduction
    During our CS 590 course this spring the we were introduced to the Netlogo computer language and various topics in computer science.   We studied several different Netlogo models thoughout the course.  One of the models that I was initially introduced to was called Wolf Sheep Predation (which is located in the Netlogo Models Library).  In that model I was thrilled by how I could change the sliders that adjusted the size of the initial populations of the wolves and sheep and then see changes in the final outcome as to which animal would eventual be exterminated and which animal would become overpopulated.  And, maybe if I happened to get the sliders set just right, the model would be in equilibrium with neither group being overpopulated or exterminated.  
    As our course progressed,  I became interested in other models that we investigated when I could again adjust the sliders (parameters) and realize that sometimes my slight changes would end up resulting in extremely fascinating results.
    During the last part of the course, the students were given the daunting task of creating our own Netlogo model as our final project.  I was a bit overwhelmed with the idea of creating one of these models on my own.  I was slightly reassured when one of my mentors for the course mentioned that we could take one of the pre-existing models, make some interesting adaptions to it, run our tests, and come up with our own new conclusions.  At that point, I was not quite sure what model I wanted to try to create with Netlogo;  I had recently been intrigued when I ran the Flocking Vee Formations model in the Netlogo Models Library that mimicked the flocking behavior of birds in flight.  I had seen different animations in Disney movies that had showed similar behaviors among the animated birds.
    So, with the Flocking Vee Formations model as my starting point, I gradually added more to the model.  Initially, my first addition was to add some hunters that would kill the flying birds.  Also, I investigated other Netlogo Models and found a neat model called the Climate Change model.   By modifying the Climate Change model I was able to add both land and sky to my hunting model.   I eventually was able to add other animals that the hunters could shoot such as buunies and wolves.  Hunting dogs were then introduced to help the hunter find the prey.  Although, not originally intended, my model had begun to take on some neat similarities to that model that had first excited me months earlier, the Wolf Sheep Predation Model.

The Problem
    In the real world there can be a debate about the need for hunting.  Animal lovers often call for other means such as sterilization of deer populations as a more humane method than hunting for reducing overpopulation.  Also, environmentalists despair when some species face extinction by poachers.  At times, overpopulation of an animal can adversely affect other species (animal or plant life) if that species happen to be a food supply.  Hunting by mankind has a very deeply ingrained appeal to many as a means to provide food on the table, control overpopulation of animal species, and also as a means of sport.  
    In the United States there is currently a protocol of having pre-arranged hunting seasons for the different popularly hunted wildlife species.  In addition, bag limits are often set to limit the number of animals that a hunter can shoot during each hunting season.  Hunting seasons can keep an animals' population under control. Hunting seasons are  planned so that they do not conflict with the breeding seasons of each animal.  Hence, the animals get the chance to replenish their population sufficiently prior to the next hunting season.  Without a defined hunting season though, hunters could keep hunting continously throughout the year and possibly drive a species to extinction.  
    As I studied the Netlogo hunting model that I created, I realized that my model could possibly give an insight into how hunting seasons really do help to keep a balance between overpopulation of different species and also reduce the chances of a species' extinction from year-round hunting.

The Equilibrium Model
The World
    The Netlogo world for the model has a pmin-xcor = -35, pmax-xcor = 35, pmin-ycor = -35, and a pmax-ycor = 35 and the patch size = 7.   The world is broken up into a lower half of land and an upper half of sky.  The sky has some randomly-placed clouds that move across from left to right.  Some non-essential items (tents, trees, and a fire) were added that are randomly place around the land area at setup.  By clicking setup several times the user can see how these items are randomly-placed each time the model is run.  
The Hunters
    The model that I created has hunters (in equal amounts of male and female).  There is a slider that allows the user to choose the initial amount of hunters.  The hunters get to randomly walk around the land area and shoot and kill whatever comes within close range  in their field of vision.  Primarily, the hunters are shooting at ducks, bunnies, and wolves.  After a randomly set period, the hunters can reproduce at a very slow rate (but only when a male hunter and a female hunter are in a close proximity).
The Ducks
    There is a slider that allows the user to choose the initial amount of ducks.  The ducks fly together in Flocking Vee Formations.  The ducks have been modified slightly from their original Flying Vee Formations model.   At random times when they are in the land area, they land, and immediately take back off in an upward direction.  If they have not landed by the time that they reach the bottom of the world, then they are forced to land, and immediately move back in an upward direction.  The birds are also able to reproduce, but only when they are in the land area.  The ducks are being hunted by both the hunters and the wolves.  Yet, during the times when they are highest in the air, they are free from being hunted.

The Bunnies
    There is a slider that allows the user to choose the initial amount of randomly-placed bunnies.  The bunnies randomly walk around the land area in a fairly fast manner.  The bunnies are able to reproduce in a fairly fast rate, yet they are being hunted by both the hunters and also wolves.  
The Wolves
    There is a slider that allows the user to choose the initial amount of randomly-placed wolves.  The wolves randomly walk around the land area.  The wolves are also able to reproduce.  The wolves are able to hunt and kill the hunters, but only if there are 2 or more wolves in a close proximity with a hunter.  The wolves also able to individually hunt the bunnies, birds, and hunting dogs.
Hunting Dogs
    Hunting dogs are created initially by the program in equal amounts to the number of hunters.  The dogs randomly walk around the land area.  The dogs are also able to slowly reproduce. If they come in close proximity to another animal, then they alert a hunter (if the hunter is in close enough proximity to the hunting dog) and the hunter then is turned to face toward the dog at that time.    
Hunting Season
    A switch has been added to the user interface that when turned on allows for a hunting season to be in place and also a non-hunting period to also take place.  The hunting seasons and the non-hunting periods are set to be equal amounts of time.  When the switch is set in the off position, then there is no such thing as a hunting season.  Hunters can hunt year-round.
Other Buttons and Monitors
    The go button is a forever button that will run the model for a total 6000 ticks which is 10 hunting seasons and then stop.  There are monitors showing the number of each of the model's key players (hunters, ducks, bunnies, wolves, and dogs).  A tick counter is visible in order to see at any time how long the model has been running.
    There are other sliders that control the formations of the birds flight.  For more detailed information about the how to use these sliders, see the Flying Vee Formations in the Netlogo Models Library.
Experimental Methods
    I am going to run the model with the hunting season switch on and using different amounts of the key players ( hunters, ducks, bunnies, wolves, and dogs) in order to see if extermination or overpopulation of any of the animal populations occurred after 10 hunting seasons (6000 ticks).  I will run the same experiments with the hunting season switch turned off (for 6000 ticks), which in effect allows the hunters to be able to hunt year-round, again checking for overpopulation or extermination of  the animal populations.


The Results Collected
    Initial Amounts    Final Amounts (after 6000 ticks)
Hunting Season    Hunters    Dogs    Ducks    Bunnies    Wolves    Hunters    Dogs    Ducks    Bunnies    Wolves
On    0    0    50    12    12    0    0    0    0    1254
On    0    0    50    12    12    0    0    2    0    1558
On    2    2    50    12    12    0    7    0    0    1116
On    2    2    50    12    12    0    2    0    0    960
On    4    4    50    12    12    4    5    13    0    50
On    4    4    50    12    12    0    5    5    0    552
On    6    6    50    12    12    3    11    7    0    49
On    6    6    50    12    12    1    8    16    0    232
On    8    8    50    12    12    0    13    8    0    256
On    8    8    50    12    12    8    10    6    179    0
On    10    10    50    12    12    10    20    21    1273    0
On    10    10    50    12    12    9    13    58    0    16
On    12    12    50    12    12    12    20    8    113    0
On    12    12    50    12    12    0    18    19    0    28
On    0    0    50    10    10    0    0    0    0    1279
On    0    0    50    10    10    0    0    1    0    704
On    2    2    50    10    10    0    5    1    0    1372
On    2    2    50    10    10    2    6    35    0    94
On    4    4    50    10    10    4    5    20    0    78
On    4    4    50    10    10    1    8    5    0    145
On    6    6    50    10    10    9    15    1    331    0
On    6    6    50    10    10    0    9    8    0    394
On    8    8    50    10    10    1    11    26    0    79
On    8    8    50    10    10    3    11    31    0    39
On    10    10    50    10    10    15    14    23    0    0
On    10    10    50    10    10    6    15    0    0    26
On    12    12    50    10    10    13    23    9    149    4
On    12    12    50    10    10    12    20    27    0    0
On    0    0    50    8    8    0    0    3    0    954
On    0    0    50    8    8    0    0    1    0    1075
On    2    2    50    8    8    0    4    10    0    381
On    2    2    50    8    8    0    6    15    0    518

  Initial Amounts    Final Amounts (after 6000 ticks)
Hunting Season    Hunters    Dogs    Ducks    Bunnies    Wolves    Hunters    Dogs    Ducks    Bunnies    Wolves
On    4    4    50    8    8    0    7    5    0    491
On    4    4    50    8    8    0    7    12    0    370
On    6    6    50    8    8    2    10    22    0    94
On    6    6    50    8    8    5    7    21    728    16
On    8    8    50    8    8    8    12    17    0    14
On    8    8    50    8    8    5    14    14    1009    5
On    10    10    50    8    8    15    16    4    4903    0
On    10    10    50    8    8    10    14    11    192    7
On    12    12    50    8    8    11    20    12    79    0
On    12    12    50    8    8    12    24    3    1852    0
On    0    0    50    6    6    0    0    14    0    367
On    0    0    50    6    6    0    0    0    0    717
On    2    2    50    6    6    0    2    40    0    160
On    2    2    50    6    6    0    6    10    0    279
On    4    4    50    6    6    2    5    18    0    124
On    4    4    50    6    6    0    4    13    0    89
On    6    6    50    6    6    6    9    61    0    0
On    6    6    50    6    6    2    11    9    0    92
On    8    8    50    6    6    6    15    15    0    16
On    8    8    50    6    6    3    12    1    0    28
On    10    10    50    6    6    10    15    3    0    0
On    10    10    50    6    6    4    17    8    55    18
On    12    12    50    6    6    12    17    10    0    0
On    12    12    50    6    6    12    18    2    0    0
On    8    8    50    12    6    4    13    4    21    48
On    8    8    50    12    6    8    13    7    13222    0
On    8    8    50    10    6    3    16    16    0    11
On    8    8    50    10    6    8    13    17    0    10
On    8    8    50    12    6    12    11    21    17    16
On    8    8    50    12    6    8    10    5    40177    0
On    8    8    50    8    4    8    14    12    0    6
On    8    8    50    8    4    5    14    20    67    8
On    8    8    50    8    4    7    12    66    6    4
On    8    8    50    10    6    2    16    15    0    132
On    8    8    50    10    6    4    12    12    0    42
On    6    6    50    8    4    1    12    25    0    79
On    6    6    50    8    4    6    12    25    0    0
On    6    6    50    10    6    6    7    132    0    35
On    6    6    50    10    6    9    8    18    0    49
On    6    6    50    12    8    6    12    11    0    40
On    6    6    50    12    8    2    8    11    0    110

    Initial Amounts    Final Amounts (after 6000 ticks)
Hunting Season    Hunters    Dogs    Ducks    Bunnies    Wolves    Hunters    Dogs    Ducks    Bunnies    Wolves
Off    12    12    50    12    12    12    18    2    0    0
Off    10    10    50    10    10    10    15    10    0    0
Off    8    8    50    8    8    7    11    18    0    0
Off    6    6    50    6    6    6    10    2    0    0
Off    4    4    50    4    4    4    6    13    18175    0
Off    2    2    50    10    10    2    3    9    0    51
Off    0    0    50    10    4    0    0    0    0    1486
Off    2    2    50    4    4    2    4    54    0    1
Off    2    2    50    12    12    0    2    14    0    455
Off    6    6    50    10    10    5    13    9    0    0
Off    8    8    50    12    12    4    15    0    0    22
Off    10    10    50    6    6    9    16    4    0    0

Conclusions
Equilibrium
    While running my experiments with the model, I found that the duck population seemed to be the one animal that stayed in equilibrium the most (ducks did not become exterminated or overpopulated on a regular basis).  Although, the duck population was a bit higher when the switch for having duck seasons was on compared to when it was off (and hunting was a continuous affair).  I had hoped for more of an equilibrium for all of the animals because of the hunting seasons.  I may need to tinker with code and ever so slightly increase the birth rate of the bunnies.
Extermination
    Another fairly certain conclusion can be stated that when the switch for duck season was off (hence continuous hunting), the extermination of both the wolves and bunnies populations by the hunters was quite regular.  Also, even when the duck hunting season switch was on, the bunnies were exterminated on a regular basis by the wolves and the hunters.  And, extermination of the bunnies and the wolves occurred more frequently when the number of hunters was large.  

Overpopulation
    Obviously, it was found that when the number of hunters was low, the populations of especially the wolves increased dramatically.   This would also occur at other times as well;  when the wolves' population increased dramatically it effected (reduced dramatically) the populations of the bunnies and birds.  
Other Minor Comments
    Looking at the data, the dog population seemed to increase at a slightly higher rate than maybe it should have.  Hence, the dogs' birth rate in the code could possibly be lowered.  Also, a similar large increase in the hunter population occurred once; hence the hunters' birth rate could be lowered slightly as well.  And, it was noticed a bit too frequently that the hunters' population decreased from captures by the wolves.  The code could probably be changed to reflect that it would need 3 wolves (instead of just 2) in close proximity with a hunter in order to kill the hunter.
Final Comments
    I enjoyed doing this project very much.  I learned a bit more about coding and am a bit less hesitant about getting involved with the NM Supercomputing Challenge.  During the spring semester,  I especially enjoyed working with Nick and Maureen.  I think that we (Northwest Region) were very lucky to have them as mentors!!!


References
Nathan, A. & Barbosa, V. C. (2008). V-like formations in flocks of artificial birds. Artificial Life, 14(2), pp. 179-188. (available at http://arxiv.org/pdf/cs/0611032)

Tinker, R. and Wilensky, U. (2007). NetLogo Climate Change model. http://ccl.northwestern.edu/netlogo/models/ClimateChange. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.

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

Wilkerson-Jerde, M., Stonedahl, F. and Wilensky, U. (2009).  NetLogo Flocking Vee Formations model.  http://ccl.northwestern.edu/netlogo/models/FlockingVeeFormations.  Center for Connected Learning and Computer-Based Modeling, Northwestern University

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Submitted by Bruce Lewis on Fri, 05/10/2013 - 12:49

Here are the files that go with my project...  Bruce