A lower number will reduce the population size. The slider DEATH-AGE represents the maximum number of years an agent can exists. If there is no variance many agents will leave the valley at once when there is a bad year. If you have variance of the harvest some agents are lucky one year and need to use their storage another year.
The slider HARVEST-VARIANCE is used to create variation of quality of cells and temporal variability in harvest for each cell. If you increase this number much more agents than the historical record is able to live in the valley. The rest is assumed the be lost in the harvesting process. The slider HARVEST-ADJUSTMENT is the fraction of the harvest that is kept after harvesting the corn. You can adjust a number of sliders before you click on SETUP to initialize the model for different values. If you click on GO the simulation will start. If you click on SETUP the model will load the data files and initialize the model.
Initial conditions of cells and agents, and the order in which agents are updated. These abstraction is simplistic, but still captures the essence of reproduction and population growth. Based on the age of the household and the availability of food, a household may give birth to an offspring household, which is representing a daughter who leaves the house and starts a new household (immediately with 3 children that require 160 kg corn per year). In the model, reproduction is modeled at the household level. Indirectly they interact by occupying potential farm plot. If not sufficient food is available, it is removed from the system. An agent is either considered to be "fit" or not fit. Fitness of agent is determined by the amount of harvest derived and amount of corn in storage. The prediction of harvest next year is the same as the experienced harvest from this year. Agents adjust the location of farming and housing if they expect that current location is not sufficient next year. the household's age increases by one year.
#NETLOGO NORTHWESTERN UPDATE#
update water sources based on input data.The new household will derive an endowment of a fraction of the corn stock. if a household is older than the minimum fission age, there is a probability pf, that a new household is generated.agents who expect not to derive the required amount of food next year will move to a new farm location.calculate the estimated harvest for next year based on corn in stock and actual harvest from current year.if agent derives not sufficient food from harvest and storage or the age is beyond maximum age of household the agent is removed from the system.calculate the harvest for each household.Process overviewĮvery year the following sequence of calculations is performed: 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. Each household is initialized by setting a household age from the uniform distribution and by setting the value of the corn stocks by the uniform distribution. These zones have agricultural productivity that is determined by the Palmer Drought Severity Index (PDSI). 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. Each cell represents a 100 meter by 100 meter space.
A household has an age, and a stock of food surplus Each household makes annual decisions on where to farm and where to settle. HOW IT WORKS Agents and the environmentĮach agent represents a household of five persons. The model is a replication of the work of Dean et al. 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. This model simulates the population dynamics in the Long house Valley in Arizona between 8.
#NETLOGO NORTHWESTERN DOWNLOAD#
Note: If you download the NetLogo application, every model in the Models Library is included. It has not yet been tested and polished as thoroughly as our other models. NetLogo Models Library: Artificial Anasazi
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