NetLogo User Community Models
## WHAT IS IT?
The model allows for comparisons between wet season and dry season dispersal patterns by pastoralists in Kenya, and was used in Boone and Galvin (2013). Vegetation growth is represented by formulas used in Fryxell et al. (2005). A variable number of wells may be initialized, and cattle must return to those wells either in the dry season or the wet season. The period animals may go before returning to wells for water Is adjustable. See Boone and Galvin (2013) for more detail.
## PROCEDURES AND LOGIC
The SETUP procedure initializes the model and prepares for a simulation by calling a series of sub-procedures. In SETUP_PARMS, parameters are set, with many coming from Fryxcell et al. (2005). SETUP-LANDSCAPE generates a local rainfall amount and sets patch variables initializing grass growth. SETUP-AGENTS creates wells used as water sources and cattle within the ecosystem. Lastly, SETUP-DISTANCES calculates the distance from the nearest cell for each of the pixels on the landscape, and standardizes those.
The GO procedure simulates time passing in the model. First, it determines if the time being simulated is within the growing season. If it is, grass is grown. If it is not, some biomass is lost, as in Fryxell et al. (2005). Cattle are colored according to thirst or mass, as requested. Grazing is then simulated using DO-HOUR, with the grazing period for a day divided into 10 hours. Mortality of cattle is then checked, using CHECK-MORTALITY. Livestock holdings are then summarized. If at the end of the year, rainfall in a new year is estimated using PREP-NEW-YEAR-PRECIP, and plots are updated using DO-PLOT.
In DO-HOUR, the behavior of cattle is set based upon their being in one of four patterns, in 1) wet-season dispersal and in the growing season, in 2) wet-season dispersal and in the dry season, in 3) dry-season dispersal and in the growing season, or in 4) dry-season dispersal and the dry season. Each influences the manner in which animals graze and move differently, as reflected in the procedures. Weight changes are then modeled and thirst is increased incrementally.
In GROW-GRASS, grass is grown using formula from Fryxell et al. (2005). CHECK-MORTALITY removes animals based on a probability relative to animal biomass. PREP-NEW-YEAR-PRECIP generates a new year of precipitation, determining if it is to be a dry or wet year overall. It also reproduces cattle, since that is to be done once per year and the month corresponds with the beginning of the growing season. DO-PLOTS updates plots.
## CREDITS AND REFERENCES
This model is by Randall B. Boone, Research Scientist at the Natural Resource Ecology Laboratory and Associate Professor in the Department of Ecosystem Science and Sustainability, Colorado State University, Fort Collins, Colorado, 80523-1499. Any use of this model or derivatives from it should cite Boone and Galvin (in press).
Boone, Randall B. and Kathleen A. Galvin. In press (anticipated, 2013). Simulation as an approach to social-ecological integration, with an emphasis on agent-based modeling. In: Understanding society and natural resources: forging new strands of integration across the social sciences. Manfredo, M. et al. (eds.) . Springer.
Fryxell, John M., John F. Wilmshurst, Anthony R.E. Sinclair, Daniel T. Haydon, Robert D. Holt, and Peter A. Abrams. 2005. Landscape scale, heterogeneity, and the viability of Serengeti grazers. Ecology Letters 8:328-335. Doi: 10.1111/j.1461-0248.2005.00727.x
R. B. Boone, March 30, 2013
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