Sugarscape
What is it?
This project explores an artificial society known as Sugarscape. This society was conceived of by Joshua Epstein and Robert Axtell (http://www.brook.edu/SUGARSCAPE). In this society, agents (red) wander around on a landscape consisting of two connected mounds of sugar (yellow). As the agents move around on the landscape they metabolize some of their existing sugar. The agents are constantly looking for new sugar, and when they find it they add it to their resources. If the agents ever eat all of their sugar, then they will die. If they get enough sugar, then they can reproduce. Each agent has a random value for its metabolism, initial quantity of sugar, and vision level (that controls how far around it can look for more sugar). The sugar itself can grow back at different rates. For a more thorough description of Sugarscape, check out the Sugarscape web site (http://www.brook.edu/SUGARSCAPE).
How to Use It
Click the SETUP button to setup the agents (red). Click the GO button to start the simulation. The N-AGENTS slider controls the initial number of agents. The HATCH-THRESHOLD slider sets the sugar level at which the agents reproduce. The CAPCITY-CONSTANT slider controls how much sugar there is initially. The MILLI-ALPHA slider controls how fast the sugar grows back if it is not growing back instantly (controlled by the INSTANT-GROWBACK? slider). The BLACK-IS and WHITE-IS sliders control the color coding of the sugar. The BIRTH slider controls whether (1) or not (0) the agents can give birth. The SHOW SUGAR button colors the turtles based on how much sugar they have. The SHOW VISION button colors the turtles based on how great their vision is. The SHOW METABOLISM button colors the turtles based on the value of their metabolism. |
Things to Notice
Watch the COUNT-TURTLES monitor to see how the agent population changes over time. You can also watch the AVERAGESUGAR, AVERAGEVISION and AVERAGEMETABOLISM monitors to see how the average values of these turtle traits change over time. The plot window graphs the total number of agents, as well as these average values, over time. The values of these traits can be influenced by the environmental conditions. Sometimes coniditions will strongly select for longer range vision, or lower metabolism.
Explorations
Under the current setting, the agents can survive and reproduce. Is the current Sugarscape capable of supporting an infinite number of agents, or is there a limit? How is that limit determined? How does the growback rate affect turtle vision and metabolism? How are these two quantities related in the population of turtles and within individual turtles? There are many extensions of this model that are described in the Artificial Societies book. Can you implement some of them?
StarLogo Features
The turtles in Sugarscape are all called from an "ask-turtles" inside of an Observer procedure. This keeps the turtles in sync with each other. This also keeps them in sync with the patch procedures that are growing back the sugar. The turtles also make use of the "leap" command. This command is like the "jump" command, except that turtles will not execute it unless there are no other turtles on the patch they are trying to get to. By calling leap within the recursive turtle procedure "relocate", it is ensured that no two turtles stay on the same patch.
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