A Fortran Program for Population Study with Minimal Computer Training

Abstract

A flexible FORTRAN II program for use in population studies is described. The program can be used after brief instruction regarding the IBM 1620 computer and the associated card reader and punches; no knowledge of programming is required. Variable parameters include age and sex distribution of the initial population; maturity limits for both sexes; frequency of reproduction for females and birthrate (each is variable by age of the female); proportion of females in each age-class that will breed; maximum number of females bred per male; proportional, density-dependent, and densityindependent mortality on an ageand sex-specific basis and in various combinations; maximum length of life; and the length of the run. Certain variables may be changed in midrun. Output may be in the form of punched cards, typed sheets, or graphs and is detailed both within each age-class and for the population as a whole. The program is available from the University of Alaska Computer Center and will be submitted to the IBM 1620 Users Group Program Library. During the course of several years and after modifications made by several people, we have formulated a number of population problems for use in teaching the basic courses in wildlife management and population ecology. Initially, one of the principal objectives was to demonstrate the inertia of a growing population subjected to harvest of females. The students first calculated population figures representing several years of unimpeded increase. Following this, various combinations of mortality were substituted, with some students working on modifications of the harvest of males, some harvesting females in various amounts, and others exploring combinations of the male and female harvests. While some feeling could thus be gained for the force of increase operating under normal reproductive conditions, a great deal of the students' time was spent on mechanics rather than learning, even with the use of desk calculators. During the past 3 years, three programs for the IBM 1620 computer have been written by graduate students or programmers in the Department of Mathematics working in cooperation with the senior author. The first, written by Ethan Scarl and presented in machine language, was found to be less flexible than was desired and has been superseded, although Scarl's efforts did much to pave the way for the second and third programs. The second program was a 20,000 storage-position FORTRAN program with less flexibility and lower potential than the third. The latter is a 40,000 FORTRAN II program and will be described below. We also wish to acknowledge some very significant suggestions made by Dr. Oliver P. Pearson, University of California, Berkeley. The FORTRAN II program was written by the junior author and has performed successfully to the point where we wish to make it available to individuals with similar problems. The program should prove useful both in teaching and in research and is expected to be applicable to management operations as well. Students in the course on principles of wildlife management now formulate problems, work them out with the computer, and present their results to the entire class. The program is written so that it can be handled by junior, senior, and graduate students who have had no previous experience with electronic computers or their programming other than