NetLogo Models Library:
Note: If you download the NetLogo application, every model in the Models Library is included.
This model simulates the population dynamics in the Long house Valley in Arizona between 800 and 1400. It is based on archaeological records of occupation in Long House Valley and shows that environmental variability alone can not explain the population collapse around 1350. The model is a replication of the work of Dean et al. (see references below).
Each agent represents a household of five persons. Each household makes annual decisions on where to farm and where to settle. A household has an age, and a stock of food surplus previous years. Each cell represents a 100 meter by 100 meter space. Each cell is within one of the different zones of land: General Valley Floor, North Valley Floor, Midvalley Floor, Arable Uplands, Uplands Non-Arable, Kinbiko Canyon or Dunes. These zones have agricultural productivity that is determined by the Palmer Drought Severity Index (PDSI).
The initial number of households is 14. Each household is initialized by setting a household age from the uniform distribution [0, 29] and by setting the value of the corn stocks by the uniform distribution [2000, 2400]. The quality of the soil of the cells is initialized by adding a number drawn from the normal distribution with standard deviation specified by HARVEST-VARIANCE.
Every year the following sequence of calculations is performed:
If you click on SETUP the model will load the data files and initialize the model. If you click on GO the simulation will start. You can adjust a number of sliders before you click on SETUP to initialize the model for different values. The slider HARVEST-ADJUSTMENT is the fraction of the harvest that is kept after harvesting the corn. The rest is assumed the be lost in the harvesting process. The default value is around 60%. If you increase this number much more agents than the historical record is able to live in the valley. The slider HARVEST-VARIANCE is used to create variation of quality of cells and temporal variability in harvest for each cell. If you have variance of the harvest some agents are lucky one year and need to use their storage another year. If there is no variance many agents will leave the valley at once when there is a bad year. The slider DEATH-AGE represents the maximum number of years an agent can exists. A lower number will reduce the population size. The slider FERTILITY-ENDS-AGE represents the maximum age of an agent to be able to produce offspring. A lower number will reduce the population size. The slider FERTILITY is the annual probability an agent gets offspring. A lower probability will reduce the population size.
POPULATION GRAPH: the blue line shows the historical data, while the red line the simulated population size.
Maps. With the MAP-VIEW chooser you can select different ways to view the landscape on the right.
If HISTORIC-VIEW? is on you will see the locations of settlements according to the data. The settlements are shown as houses, and the size (area of the house shape) is proportional the number of households on that location.
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NetLogo replication of Artificial Anasazi model by Jeffrey S. Dean, George J. Gumerman, Joshua M. Epstein, Robert Axtell, Alan C. Swedlund, Miles Parker, and Steven McCarroll
This model is a lightly adapted version of the prior replication work of Marco Janssen (with help of Sean Bergin and Allen Lee) who reimplemented the Artificial Anasazi model in NetLogo (the original model was written in Ascape).
The code of this complex historical model is in the process of being refined by the NetLogo team, and still differs greatly from the usual standards of the Models Library.
Janssen's version of the model is available at: https://www.comses.net/codebases/2222/releases/1.1.0/. (Furthermore, this "Info tab" is adapted from the ODD model documentation that accompanies that model.)
Janssen's replication is discussed further in the following academic journal paper, which curious readers are highly encouraged to examine:
Janssen, Marco A. (2009). Understanding Artificial Anasazi. Journal of Artificial Societies and Social Simulation 12(4)13 <http://jasss.soc.surrey.ac.uk/12/4/13.html>.
Some follow-up work on calibration and sensitivity analysis of this model is published in:
Stonedahl, F., & Wilensky, U. (2010). Evolutionary Robustness Checking in the Artificial Anasazi Model. Proceedings of the AAAI Fall Symposium on Complex Adaptive Systems: Resilience, Robustness, and Evolvability. November 11-13, 2010. Arlington, VA. (Available: http://ccl.northwestern.edu/papers/2010/Stonedahl%20and%20Wilensky.pdf)
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Copyright 2010 Uri Wilensky.
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