Caribou – Wolf Interactions

• http://www.youtube.com/watch?v=nK1JOmMQ5Fc

Issues with Simulations• Realistic Movement

– Moving toward desired areas– Keep animals from getting “stuck”

• Validation

• Boundary conditions– What happens at the edges?

• Disappear/die (need immigration as well)• Reverse direction• Wrap to the other side (not realistic)

• Model stability

• Model complexity/Performance

Moving Toward Desired Areas

• Use Distance Raster– Desired area:

• Spawning ground, feeding grounds

– Destination is desired area– Pixels with lower cost are closer to desired

area– Animals move to adjacent pixels with lower

cost

Moving Through Networks

• Use polylines with network nodes

• Move in direction (or against) of polylines

• Need to make decisions at nodes

Getting “Stuck”

• Certain conditions arise and animals can become stuck and just move back and forth– Add additional randomness– Examine environmental layers for unrealistic

values• Streams not flowing perfectly down hill• Bays not connected with the ocean

Validation

• Run models over and over again

• Record locations, births, deaths, feeding– Create probability surfaces

• Validate against existing datasets– Are observations/measurements within the

predicted areas?– Could use likelihood/AIC…

Model Stability

• Density dependence– Most species struggle more when crowded– Reduces food availability, increases disease– Places a control the number of individuals

• Balancing birth rates and death rates

• Realistic lifecycles, predation rates

Model Complexity

• Typically there are lots of agents

• Need to keep the behaviors and attributes simple

• The group behaviors are typically more complex than expected from the individuals

• Model a population– Convert “groups” of individuals to

populations when they cluster

Monte Carlo-Markov Chain

• Markov Chain:– A series of states of being that have

probabilities associated with transitions (i.e. the state is not deterministic but has some stochastic component).

Performance

• Select the right resolution for rasters– High enough to be realistic– Low enough for speed– May have to just simulate a smaller area

than desired.

3D and Temporal

• Simulations are almost always temporally based

• 3D is common but requires more hardware/time– Also requires special software and 3D data

Ecological Modeling

• Water, carbon, nutrient cycling

• Trophic models

• Population models

• Predator/Prey

• Disease

wsu.edu

Sustainable Fisheries

www.niwa.co.nz

Can operating rooms in Second Life teach

real doctors?- Discover

World of Warcraft

Sims

Tools

• NetLogo

• HexSim

• MASON Multi-Agent Simulation Toolkit

• Repast

• Programming!– Python– Java

• Books: “Agent-Based Models of Geographical Systems”

Envision – Policy Simulation

Simulations

• Parameterization– Based on mechanisms/theories– Typically include random effects– “Tweeked” to fit reality

• Validation– Run over observed space and time

• Do simulated measures match observed?

– Run it over and over• Observed fit into “Confidence interval”?

Simulations

• Startup:– Either simulate a known situation– Or, run until reaches an expected state

• Stability– Populations tend to breed out of control or

die out over time– Build in realistic limitations

NetLogo

• Environment for 2D simulations• Easy to program• OpenSource, free• Was a “kids” language • Now used for education, visualization,

simple simulations• Can install outside “Program Files”• Run NetLogo.exe• See included Tutorials

NetLogo – Model Interface

NetLogo Design

• NetLogo is a world made up of: – Turtles: The agents that move – Patches: Agents that do not move (i.e.

grass, buildings, roads) – Links: Connections between turtles – Observer: Oversees the action

Ecological Modeling

• Combination of cellular automata and individually based models:

Grid of cells(raster)

Individuals

NetLogo - Code

HexSim

• Visit Hexsim.net to download

• Decompress the folder

• Can run “Hexsim.exe” from within the folder without other installation

• See the “Examples” on the HexSim website to get started– The User’s Guide has good information on

how HexSim works

HexSim Basics

• Set the workspace:– HexSim -> Set Workspace– Select a “*.grid” file

• Double click on a scenario to “open”– Adds a tab for that scenario– “Scenario” menu items work on the currently

selected tab

• View spatial data:– In the “Spatial Data” panel, open items– Double-click on “-> 1” to show the data

HexSim Basics

• Select “Scenario -> Run Simulation”

• Save an XML file for the run

• Click “Start” in the window that is displayed

• These examples are not yet parameterized so you may need to modify them to do something interesting

Comparison of Software

• http://en.wikipedia.org/wiki/Comparison_of_agent-based_modeling_software

Simulation Modeling

• Plate tectonics:– http://www.youtube.com/watch?

v=ryrXAGY1dmE

• Wolf simulation game– https://www.youtube.com/watch?v=idr0A-

yl56Q

Possible Simple Models

• Fire w/fire fighters

• Zombies and humans

• Reef fish

• Wolves and elk

• Invasive species (w/managers)