Data used or generated by PAS programs are stored in files called *.DAT. Model parameters are stored in files called *.MO1 for single-species models and *.MO2 for two-species models. Autocorrelation data in files called *.ACF and partial rate correlations in files called *.PCF ( * refers to a name you supply while the riders .DAT, .MO1, etc. are added automatically by PAS.) . The PAS Time Series Analysis program P1a uses population census data to identify possible forms for R-functions generating observed population fluctuations. The program is most appropriate for organisms with discrete generations or breeding cycles; e.g., animals with a single generation per year or that breed at a particular time each year. However, it can also be used, with some caution, on data from continuously breeding populations.
All data should be in the form of population density counts containing all age classes or developmental stages, or of a particular stage (e.g., eggs, adults, etc.) taken at discrete and equidistant points in time (e.g., at the same time each year). For example, the density of insect eggs measured in early May each year for 20 years.
PAS data files are stored in ASCII format. Data files can be built while running P1a, the single-species time series analysis, or with a spreadsheet or line editor. If data are entered other than by P1a, they must be entered on separate lines in the following format:
Before entering data you should consider rescaling them so that the smallest number is larger than 1 (preferably > 10). This can be done by multiplying all the data by a scaling constant. For example, if the smallest datum is 0.67 insects per square meter, then one can adjust the sample size to 100 square meters, in which case the smallest datum becomes 67.0 per 100 sq. m. You must then multiply all other data by the same scaling constant. Occasionally the data may consist of very large numbers, in which case it may be advisable to scale them down. For example cone beetle densities in Tutorial #1 were actually measured per acre but were rescaled to numbers per 0.1 acre by dividing all data by 10. Scaling the data to numbers that are neither too large nor too small produces better graphics and eliminates negative logarithms but has no effect on the analysis itself.
We also recommend that data files be organized on floppy disks or sub-directories according to subject; e.g., insects, mammals, fish, birds, etc.
PAS allows you to save all sorts of data on disk, including data you enter, data simulated by models, model parameters, and so on. These data can be accessed by other programs (word processors, spreadsheets, etc.) as well as by other PAS programs.
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