A Computer Program for Calculating Degree of Biogeographical Resemblance Between Areas

A program, written in the computer language BASIC, is described that calculates by various formulas the degree of biogeographical resemblance between areas. The various formulas are described, and the proper machine instructions for each are indicated. In their recent analysis of the distributional patterns of North American mammals, Hagmeier and Stults (1964:131) summarized the various formulas that have been proposed by biogeographers for use in the analysis of the degree of relationship between two areas. They chose three of these formulas to use in their calculations, and listed four more that had been suggested and used by various authors. The decision by Hagmeier and Stults to use the "Coefficient of Community" and the "Simpson Coefficient" was based on the simplicity of the formulas and the ease with which they could be calculated. Several of the other formulas used, such as the "Resemblance Equation" of Preston (1962), include logarithms, square roots, or consultation of tables, and the increased amount of effort involved has interfered with their use by biogeographers. Since most of the formulas were introduced as attempts to eliminate difficulties resulting from different sample size, it seems likely that a worker might wish to see what results all would give with his data. In the past, however, biogeographers have usually chosen one formula, because if the number of localities involved is very large, the amount of time devoted to the calculation of values is almost prohibitive. The advent of computers greatly facilitated such calculations, and there has been an increase of attempts to deal with such data. But the computer has presented additional problems of accessibility, programming, and cost. Time-shared computers, which I have discussed elsewhere (Peters, in press), have eliminated these problems by using a teletype connection to a central computer used simultaneously by many subscribers. Since the teletype can be installed any place, access is maximum. The cost, because of the simultaneous use, is very low, and is well within the range of tolerance of museum budgets. The programming, representing a major breakthrough, is usually in the user oriented computer language called "BASIC," developed at Dartmouth University. I have written a program for such a time-share computer that will calculate all of the formulas for biogeographic comparisons known to me. This program runs all formulas at the same rate of speed, and the difficulties presented by square roots or logarithms no longer exist, since the machine can do all such calculations. It should be clearly understood at this point that the biogeographer does not need to understand the jargon of the program, nor does he need previous experience with a computer. I am assuming only that he has access to a teletype connected to a computer, and that he either knows or will take five minutes to learn the rudiments of teletype operation and how to contact the computer. After that, all he need do is to insert his data as directed here, and watch the answers being printed out for as many different formulas as he wishes to test. The following program is written in BASIC. There should be little difficulty in converting it into another language, if anyone reading this paper has access to a computer that does not accept it. Ordinarily, this will have to be done by a computer programmer, because, although work is being done on machine translation