“Rabbits and wolves”

Introduction

The computer simulation named “Rabbits and wolves” is about models and simple systems. In the simulation, there are three main organisms, rabbits, wolves and grass all put together in a forest ecosystem. An ecosystem is a set of organism within a defined area or volume that interact with one another and with their environment (Miller & Spoolman). A system is a collection of elements or components that are organized for a common purpose (Rouse, 2005).
The purpose of this simulation is to see how these three organisms will interact with one another in the same environment. We will see how the populations of these organisms change by modifying parameters specific to each organism and how changing the start up parameter of an organism can affect the way the others grow.

Objectives

1. To view and interact with a simple scientific computer model. 2. To determine how simple changes in populations of one organism will affect populations of organism in the same system. 3. To use a computer model to complete objective 2.

Hypothesis

Placing rabbits in a larger forest will not only allow them to grow better and have enough sustenance but also to avoid being eaten by wolves.

Results

The default parameters are the following:

| Rabbit | Wolf | Maximum food capacity | 45 units | 200 units | Metabolism rate | 3 units/stage | 2 units/stage | Reproduction age | 10 stages | 10 stages | Probability of reproduction in a suitable environment | 50% | 50% | Minimum food requirement to reproduce | 40 units | 120 units | Maximum age | 25 stages | 50 stages | Initial number of | 20 | 5 | Initial food level | 10 | 150 |

Graph 1 Evolution of the wolf and rabbit population in their natural environment

The first graph shows the population statistic when the simulation is running with the default parameters for 200 iterations.

Graph 2 Evolution of the rabbit population without wolves’ presence

Wolves have been removed from the start up parameters. The simulation runs for 200 iterations.

Graph 3 Evolution of the rabbit population without wolves’ presence with a decrease of its means of sustenance Wolves are removed from the start up parameters and the initial grass value has been cut in half. The simulation runs for 207 iterations.

Graph 4 Evolution of the wolf and rabbit population in a smaller environment than the default parameters The default parameters are running but the size of the forest changed from medium to small. The simulation runs for 221 iterations.

Discussion My first objective was to view and interact with simple computer model. I was able to represent in terms of parameters the variables, watch on the simulation and examine the results. My second objective was to determine how simple changes in populations of one organism would affect the populations of organisms in the same system. I’ve changed parameters of each one of the variables and I deducted that making changes in the population of one organisms could influence the populations of other organisms. My third and last objective was to use a computer model to complete objective 2, which I don’t know if my interpretations are correct. In the first graph, with the default parameters, we can see that the rabbit population grew rapidly at first due the large amount of sustenance (grass) available and the wolf population was too low to eat them all. As their population was growing faster, after a short time, the level of sustenance started to decrease as well. All the rabbits died because the grass wasn’t growing fast enough to feed of all them. After a dramatic extinction of the rabbit population, the level of grass increased and reached its full capacity since there were no more rabbit to eat it. In the second graph, with the factor “predation” (wolves) removed, the rabbit population was growing fast with a vast amount of grass. As the rabbit populations increased the grass level decreased. As the rabbit population declined, the grass was growing back. On the graph, you can observe an up and down variation between the rabbit population and the grass amount. We can also see that it took time for the grass to renew due to the continual growth of the rabbit population. In the third graph, with the initial grass rate cut in half, the number of rabbits went down. They didn’t have enough food to reproduce at a high rate. The results in this graph showed pretty much the same results in graph 2 except that the grass rate was lower making the rabbits multiply slower. In the fourth graph, with a smaller forest ecosystem and plenty of grass, the rabbit population grew at a moderate rate at first because the wolves were eating some of them and then they started to multiply at high level. The rabbits’ fast growth made the grass level to decline and they were perishing due to starvation. Only wolves and grass were left in the ecosystem and the wolves also started to die because they can’t eat grass. It would really be interesting to add some other variables to this ecosystem. We could have added factors like bad soil, which wouldn’t allow the grass to grow well, the rabbits would die and so would the wolves with starvation. More preys could have been added to so that the wolves wouldn’t have only the rabbits as food or more predators to decline the rabbits population. If we were to add human to that ecosystem, they would take over all these three variables. They would use rabbits as food, kill the wolves not to get killed by them, and probably remove the grass to make some space for them, like building houses or use it to feed their cattle, trees in the forest to make fire, or cover their roofs. Human beings can be selfish. They use anything around them to subsist their needs. Computer simulation model are very crucial for prediction. They show real data and allow us to see how variables in the same ecosystem interact and the way they may have effect on each other as bad or good. It also make us understand better our environment, it is a good prevention tool against multiple factors that may contribute to destroy our surroundings. Resources Environmental Science: problems, connections and Solutions. 14th Ed. Miller G. Tyler JR. & Spoolman Scott. Brooks/Cole. Pacific Groove, CA. 2010/2013. Rouse, Margaret. “What’s a system?” techtarget.com. April 2005.