POPSIZE README FILE --------------------------------------------------------------------------- CONTENTS: 1. What is PopSize? 2. Copyright and Disclaimer 3. Installation 4. Running PopSize 5. Technical Stuff 6. Contact Information ---------------------------------------------------------------------------- 1. What is PopSize? The mark-recapture (or capture-recapture) method is used by ecologists to estimate the size of animal populations. First a sample of individuals is captured, marked and then released. Later, a second sample is taken and the number of marked individuals determined. If one makes certain assumptions, the population size can be estimated from the proportion of marked individuals in the second sample. I wrote PopSize to give my ecology students a deeper insight into the mark-recapture method. I use it to supplement an exercise carried out with real populations in the field. With this program students can run hundreds or thousands of simulated mark-recapture experiments and observe the result. Sample size, mortality and emigration can all be varied to see how this affects the estimate. There are also two models to choose from. In addition to what it teaches about the mark-recapture method this program also gives students a more intuitive grasp of statistical sampling in general. For example, students should have a better understanding of what a 95% confidence limit means after running the simulation 1000 times and observing that the confidence limits do not always encompass the true population size. The professional literature on mark-recapture, capture-recapture and capture-remove techniques is immense. It is not the purpose of this program to elucidate every model or technique that is in common use. In particular, the program does not cover the multiple recapture methods. This program is a teaching tool for beginning to intermediate ecology students, though it may also be useful in graduate courses. ----------------------------------------------------------------------------- 2. Copyright and Disclaimer This program is freeware, but is not public domain. It is copyrighted by Robert P. Gendron. You are free to use this program only if you adhere to the following conditions. a. Under no circumstances may you sell this program. You are, however, encouraged to make it freely available to your students. b. If you distribute the program to others you must do so with all of the supporting program files and this Readme file. If you distribute the program to students in your class you do not have to include the laboratory exercise or worksheets since you may prefer to use your own. c. You are welcome to use and modify the accompanying laboratory exercise and worksheets as long as some mention is made of the original source. d. If you use this program in your course you must let me know. Comments and suggestions would also be appreciated. If you develop teaching materials I would like to see them for possible use in my own course. I have spent many hours developing this program and have tested it on a variety of machines (386 and Pentiums running Windows 3.1, 95 and XP). However, I make no claims or warranties. You use it at your own risk. If you have difficulty running the program or have questions send me an e-mail and I will try to help. If you find a bug please let me know. If I can fix it I will send you a corrected version of the program on disk. ----------------------------------------------------------------------------- 3. Installation If you downloaded PopSize from my web site (http://nsm1.nsm.iup.edu/rgendron) you chose either the version with or without the setup program. The latter version is smaller for faster downloading, but you have to copy files to the appropriate directories using Windows Explorer or Program Manager. Installing PopSize without the setup program a. Using Windows Explorer or Program Manager create a directory where you want the program to reside (e.g. C:\PopSize). Download or copy POPSIZE.ZIP to this directory. b. Unzip the file. c. Copy the 13 DLL and OCX files to your Windows System directory. (If you already have these files on your computer only overwrite them if the copies that came with PopSize are newer). d. Use the program manager or explorer to run PopSize.EXE. If you wish you can use Explorer to create a shortcut to the program. Installing PopSize with the setup program a. Download or copy PopSizeI.zip to a temporary directory and then unzip it. b. Run Setup.exe. Setup decompresses files and copies them to the appropriate directory. It allows you to specify where to put the main PopSize program (e.g. c:\popsize). A new directory will be created if it does not already exist. The supporting DLL and OCX files will be copied to the Windows System directory. However, the Setup program will *NOT* copy an older version of the file over a newer version. Files will be replaced only if the ones included with PopSize are newer. If replacing old Windows DLL files makes you nervous you can take the precaution of making backup copies of these files in a temporary directory. Then if a problem develops you can restore them. These files are listed in a text file called SETUP.LST. c. The Setup program will create a separate folder called PopSize where you will find the program. ----------------------------------------------------------------------------- 4. Running PopSize There are two main screens in PopSize, one for setting the parameters and one for viewing the simulation. In the Parameter Input Screen you can set: True Population Size Number of animals captured in the first sample - these are marked and released Number captured in the second sample The relative catchability marked vs. unmarked animals Percent mortality of marked animals Percent mortality of unmarked animals Percentage of marked animals emigrating Percentage of unmarked animals emigrating Percentage of marked animals that lose marks In addition there are several option buttons that let you choose between, Two models for estimating population size Three formulas for calculating confidence limits Two confidence limit sizes (95% or 99%) On the display screen results are shown in two graphs. The top graph shows, for each simulation, the estimated population size and confidence limits. You can see at a glance if the confidence limits encompass the true population size. After running the simulation a number of times it becomes obvious if there is a bias in the estimate (e.g. if there is differential mortality of marked animals). The bottom graph shows a frequency distribution of estimates. To the right of the graphs are displayed the results of the last simulation: number of marked animals recaptured estimated population size upper & lower confidence limits Also displayed are some cumulative results: # times the confidence limits hit or missed the true population size average estimate of population size average width of the confidence limits average deviation of the estimate from the true population size To see how I use this program in you class look at the attached Word document (POPSIZE.DOC). This includes a laboratory handout, worksheets and instructor notes. ------------------------------------------------------------------------------------- 5. Technical Stuff I wrote PopSize in Visual Basic 4.0 Professional Edition. This program will run on Windows 3.1, Windows 95 and WindowsXP. The basic algorithm behind the simulation is fairly simple and uses a random number generator is to simulate the stochastic sampling process. The true population size and the size of both samples is set by the user. The probability that a captured animal is marked is determined by the size of the first sample, any mortality or emigration that occurred and any sampling bias. To simulate the process of collecting the second sample the program generates a random number for every individual in the sample. If the number is less than the probability of capturing a marked animal the animal is considered to be marked, otherwise the animal is unmarked. This continues until the second sample is complete. ---------------------------------------------------------------------------------- 6. Contact Information If you use this program I would like to hear from you. My address is Robert P. Gendron Biology Department Indiana University of Pennsylvania Indiana, PA 15705 rgendron@iup.edu http://nsm1.nsm.iup.edu/rgendron