Read Me First
Nearly all of the models used to simulate population dynamics in the book: An illustrated guide to theoretical ecology by Ted J. Case can be downloaded from this web site. These programs are written in the systems modeling software Stella ® (1999, High Performance Systems, Hanover, New Hampshire) and in a few cases Matlab® (The Math Works). In both cases, the individual models will run on a PC or Macintosh computing platform with the appropriate software.
A special run-time version of Stella ® that will allow users to run the models and change parameters, can be downloaded free from the High Performance Systems website: http://www.hps-inc.com. This program allows the user to change parameters and initial conditions, but not add new variables and parameters. A guide to using the Run-time Stella is also available from the Stella website. Each Stella model consists of three pages. The first page gives the output illustrations and input devices for the model. An example of this page follows. Note the arrows pointing to important control features for observing the model and its output.
The next two pages of this model are:
Students may purchase a discount edition of Matlab from The MathWorks, Natick Massachusetts (http://www.mathworks.com). At the time of writing, the most recent version is Version 5. The Matlab models for this book, however, should be compatible with earlier versions.
To run a Matlab model, the name of the model must be typed in the command window. The files containing the model all have the suffix ".m", but this does not have to be typed. The files may be opened in a separate window for editing. An example of these two windows follows:
In this case we could run this program by typing "compete2sp" after the prompt: EDU>
in the top control window. Matlab is case-sensitive, so you can not exchange capital letters for lower case ones. After typing the file name, hit the return key and the program executes and asks for some input values, then it produces the following graphs, which show up in their own windows.
In the edit window of Matlab, you may also change parameters and initial conditions, then re-save the program, and run it again from the command window. A useful key to use in the command window is the "up arrow",
·. By hitting this key, the command window will automatically recall the last command typed, e.g. the name of the program that you previously ran. By typing a few letters, and then ·, the last command beginning with those letters will be recalled; then hit the return key to re-execute that command. Roughgarden’s "Primer of theoretical ecology" (1998, Prentice Hall) is an excellent introduction to Matlab as applied to ecological modeling.The models for this book are bundled by the Chapter in which they are introduced. In most cases, the parameters are set to produce figures as they appear in the book but students should explore how changes in parameters and initial conditions change results.
Finally, another neat approach is Ecobeaker for Macs or PC’s developed by Eli Meir. These are individual-based models. The web site is http://www.ecobeaker.com.