![]() The global Cost per Goat can be viewed in the COST PER GOAT monitor. Their revenue for the last day will be displayed in the CURRENT REVENUE monitor and their total assets in the TOTAL ASSETS monitor. The MY GOAT POPULATION monitor will display the number of goats each student owns. ![]() GOAT POPULATION - number of goats on grazing field over time (in days)Īfter logging in, the client interface will appear for the students, and if GO is pressed in NetLogo, they will be assigned a farmer which will be described by the color in the MY GOAT COLOR monitor. MILK SUPPLY - amount of milk produced over time (in days)ĪVERAGE REVENUE - average revenue of all farmers over time (in days) GRASS SUPPLY - amount of grass available to graze upon over time (in days) GOAT POPULATION - number of goats grazing in the common area MILK SUPPLY - amount of milk produced each dayĪVG-PROFIT/DAY - amount of revenue collected from milk sale per day ![]() GRASS SUPPLY - amount of grass available to eat GRAZING-PERIOD - the time frame in which goats are allowed to graze each day GRASS-GROWTH-RATE - amount of grass growth for each tick of the clock INIT-NUM-GOATS/FARMER - initial number of goats per farmer at the beginning of the simulation LOGIN - allows users to log into the activity without running the model or collecting data SETUP - returns all farmers, goats, and patches to initial condition and clears the plot. Teacher: To start the simulation over with a new group, stop the model by pressing the GO button if it is on, press the RESET button in the Control Center to kick out all the clients and follow these instructions again from the beginning. Restart the simulation by pressing the GO button. Teacher: To run the activity again with the same group, stop the model by pressing the GO button, if it is on.Ĭhange any of the settings that you would like. To curb buying incentives of the students, increase the COST/GOAT slider.Īny of the above mentioned parameters - GRAZING-PERIOD, GRASS-GROWTH-RATE, and COST/GOAT - may be altered without stopping the simulation. Please note that you may adjust the length of time, GRAZING-PERIOD, that goats allowed to graze each day.įor a quicker demonstration, reduce the GRASS-GROWTH-RATE slider. Then press the GO button to start the simulation. Have the students acquaint themselves with the various information available to them in the monitors, buttons, and sliders. Teacher: Once everyone has logged in, turn off the LOGIN button by pressing it again. Press the LOGIN button to allow people to login.Įveryone: Open up a HubNet Client on your machine and enter your name, select this activity, and press ENTER. If you do change the settings, press the SETUP button. Optional: Zoom In (see Tools in the Menu Bar) Teacher: Follow these directions to run the HubNet activity. ![]() Ultimately, the common grazing area does not contain enough grass to sustain the overcrowding of goats, and the milk-supply as well as the farmers' revenues decline. With the increase of the GOAT-POPULATION, GRASS-SUPPLY gradually decreases. But suppose, then, that due to the farmers' own incentive to increase their own wealth and each farmer's indifference to the other farmers' decision to purchase goats, each farmer continues to buy more goats. Initially, the abundance of GRASS-SUPPLY of the patches can sustain the goats and their grazing and leads to increasing milk-supply and increasing revenue. The amount of grass they eat is equivalent to how much milk they can produce (and ultimately, the amount of profit they produce for the farmer).Īfter the GRAZING-PERIOD, the farmers may choose to buy more goats to increase their own wealth. The goats move around the screen for a time span of GRAZING-PERIOD to graze and feed themselves. They own INIT-NUM-GOATS/FARMER when they join the simulation. (The efficient market theorem states that agents, looking out for their own best interest, leads to the most efficient social outcome. This is a counterexample to the efficient (as defined in "Pareto efficiency") market theorem. Depending on the actions of the participants, the outcome may demonstrate a phenomenon called the "tragedy of the commons", where a common good or resource is over-utilized. In this example, the common resource is represented by the common grazing area, used by goat farmers to feed their goats. This model simulates the utilization of a common resource by multiple users. Note: If you download the NetLogo application, all of the HubNet Activities are included. (back to the library) Tragedy of the Commons HubNet NetLogo Models Library: Tragedy of the Commons HubNetįor information about HubNet, click here.
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