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## NetLogo User Community Models

WHAT IS IT?

This model explores the stability of predator-prey ecosystems with fragmented habitats.

HOW TO USE IT

The general rule: proceed left to right, top to bottom. Never go backwards or things might crash.

1 - init (clear all), set movie and file switch (to produce "out.mov" and "out.txt", respectively)
2 - setup (defines grass and random predators and prey)
3 - draw walls for habitat fragmentation (optional)
4 - draw doors on the walls to connect fragments, or make openings w/ the mouse (optional)
5 - draw a box around the field (suggested - otherwise it's a torus!)
6 - go..

Parameters:
INITIAL-NUMBER-SHEEP: The initial size of sheep population
INITIAL-NUMBER-WOLVES: The initial size of wolf population
SHEEP-GAIN-FROM-FOOD: The amount of energy sheep get for every grass patch eaten
WOLF-GAIN-FROM-FOOD: The amount of energy wolves get for every sheep eaten
SHEEP-REPRODUCE: The probability of a sheep reproducing at each time step
WOLF-REPRODUCE: The probability of a wolf reproducing at each time step
GRASS-REGROWTH-TIME: How long it takes for grass to regrow once it is eaten

Notes:
- one unit of energy is deducted for every step a wolf takes
- when grass is included, one unit of energy is deducted for every step a sheep takes

THINGS TO NOTICE

With increasing predator quality ("wolf gain") spatial waves can form. High densitiy waves typically lead to extinction of prey and then predator. Howwever, introducing barriers and connectors improves coexistence.

THINGS TO TRY

Try different framgentation schemes with different number of boxes and doors.

EXTENDING THE MODEL

There are many possibilities, the most obvious being the introduction of different migration speed (and different life cycle) for predator and prey.

CREDITS AND REFERENCES

George Kampis and Istvan Karsai 2010: Breaking Waves in Population Flows, in: Kampis, G, Szathmary, E., Karsai, I, Jordan, F. (eds): Darwin Meets von Neumann. Proceedings of the 10th European Conference on Artificial Life, Springer, in press.

Istvan Karsai and George Kampis 2010: Connected Fragmented Habitats Facilitate Coexistence, submitted.

Wilensky, U. (1998). NetLogo Wolf Sheep Predation model. http://ccl.northwestern.edu/netlogo/models/WolfSheepPredation. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.