Populus 2.10, August 1992 Overview The Populus software contains a set of simulation model

Master Index Current Directory Index Go to SkepticTank Go to Human Rights activist Keith Henson Go to Scientology cult

Skeptic Tank!

Populus 2.10, August 1992 Overview The Populus software contains a set of simulation models that we use in teaching population biology and evolutionary ecology at the University of Minnesota. All of the simulations share a common format, as follows: After a model is chosen from the menu, the program displays (optionally) several screens of background material which introduce the mathematics and end with basic references. Next, there is a screen listing all of the input parameters; students can move among the parameter boxes and change initial defaults to values of their own choosing. The program maintains a record including permissible maxima and minima for each parameter and filters input values accordingly. Usually there are several possible outputs (e.g., N vs T graphs and phase planes) which can also be selected from the parameter input screen; alternatively, students view the different outputs in sequence, by pressing the space bar between views. Context-sensitive help screens are available (press ) from the input and output screens of every model, and by pressing twice one can see a menu of additional help screens which includes discussions of function and editing key assignments implemented by the program, printing protocols, video options, etc. Hardware Requirements The program is written in Turbo Pascal to run under DOS on IBM and compatible computers. To implement the full range of Populus features, about 500KB of RAM are necessary, free of memory-resident utilities and drivers. The program will use LIM expanded memory, reducing the frequency of disk reads and speeding program execution. Although the code will emulate an xx87 coprocessor if one is not present, many of the models are computationally intensive and will run much more rapidly on a machine with the floating-point chip. Since overlays are read during program execution, the program files (populus.exe, populus.ovr and populus.txt) should be copied to a hard disk (or a RAM disk emulator). If this is not possible, the program will run from two 720K (or larger) diskette drives, and will prompt users for a path to the Populus.ovr file. Version 2.10 will run on any IBM-compatible video system which permits graphic displays, including "Hercules," "CGA," "EGA," "VGA," and "IBM8514." In most cases, the software will recognize and accommodate your video system automatically. If your display emulates one of the color systems in shades of gray (as many LCD screens do, with varying success), consider using the option which forces output to the monochrome mode. The IBM8514 system is detected as VGA by Turbo Pascal; IBM8514 users who desire full 1024x768 resolution (beautiful!) can select that video mode from the Populus Options Menu (Alt-O) and save a populus.cfg file to disk so that their preferred configuration loads automatically each time the program is run. Populus 2.10 contains a set of commercially produced drivers by Ryle Design that supports a wide variety of printers, including 9-pin and 24-pin dot matrix printers, HP laserjets and deskjets, the HP paintjet, and printers implementing the Postscript page-description language. Print files may also be saved to disk and sent to the printer later using the DOS Print command. Set the appropriate printing configuration on the Populus options menu. Note that Postscript supports graphics-mode printing only. Our introductory narratives and all outputs are rendered in graphics mode, but the parameter inputs and help windows are text mode screens. To print them on a postscript laser printer you will have to set it up as an HP emulator. Bells and Whistles For many problems and exercises it is desirable that students be able to read numerical values accurately from the graphical output. We have included several new video routines for this purpose. A gridding function (press ) plots horizontal and vertical lines from the major axis ticks, and a second grids the minor ticks. A third press toggles the feature off. Our video zooming function (press ) pops up a rectangle whose corners can be moved (with the cursor keys) to any point on screen. Pressing then zooms this new rectangle to full-screen size. By zooming in on an interesting equilibrium region and gridding the output, final frequencies can be read with any desired degree of accuracy. For many time trajectories of ecological dynamics, comparison of arithmetic and logarithmic plots has pedagogical value. Populus plots arithmetic time trajectories by default but allows you to toggle a semi- logarithmic plot (press ). Like other video utilities in Populus, the feature is turned off (and the screen-bottom options line is cleared) with the same keystrokes that turned it on. Populus models that display in the lower-right corner of their input window include a routine that allows on-screen comparison of outputs resulting from two different sets of parameter values. To implement this feature, simply toggle . Graphical output from the current parameter values will be plotted in the normal colors, while output of the previous run will be shadowed in black. A second press of toggles the graphical comparison routine off. Stability analyses are important in helping students to understand the dynamics of ecological and evolutionary models, and we have provided a rich set of stability tools in Populus. Many of the genetical simulations begin from several different starting gene frequencies automatically. Optional stability analyses are also available with the phase-plane graphs of ecological dynamics. To implement this feature, press after a phase diagram is complete; a cursor will pop up and can be moved to any point on the screen. Pressing will then initiate a trajectory from that point, and the dynamics can be run forward or backward. Alternatively, multiple-starting-point stability analyses may be run by pressing after . The program will then initiate trajectories from the perimeter or from a gridded pattern of points (the number and position of starting points is set from the options menu) to illustrate the stability of internal equilibria. In addition to these video utilities, Populus now includes several file- handling routines. Output data from any of the simulations can be saved to disk for analysis using a spreadsheet, statistical package, or graphics editor. To do so, call up the options menu after running your simulation, and specify a path and name for your data file. Similarly, Populus can save to disk and reload sets of model parameter values; you might use this feature to save a series of parameter files that show particularly instructive examples, and ask your students to load, run, and analyze them as part of a lab exercise. Finding Documentation This file contains only a brief introduction to Populus. Full descriptions of each feature and a listing of the keystrokes necessary to call and implement it are built into the program, and are accessible from the Main Help Menu. To see this menu, press (or if you are already in one of the model parameter or output screens, press twice, to get past the context-sensitive help). We recommend a tour of the Main Help Menu as the quickest way to familiarize yourself with the capabilities of Populus. Sponsorship and Distribution This software has been underwritten by IBM, the University of Minnesota, and the Undergraduate Course and Curriculum Development Program of the National Science Foundation (USE-9150887, USE-919155967); it is not a commercial venture and we encourage you to distribute it without charge to any colleague or student who will put it to good use. If you find a bug please tell us. We will fix it and provide you with an update. Don Alstad Department of Ecology, Evolution & Behavior University of Minnesota 318 Church St. SE Minneapolis, MN, USA 55455-0302 612-625-0488


E-Mail Fredric L. Rice / The Skeptic Tank