ANALYSING INTERACTION FROM RADIO-TRACKING DATA: PROGRAMS FOR PCs
Three programs can be downloaded here, for analysis of interaction between concurrently tracked pairs of individuals (DYNAMIC), overlap and concordance in the utilisation distributions of pairs of home-ranges (STATIC), and definitive shifts in the location of a range over periods of weeks or months (DRIFT). For more background information, see:
The programs run on any IBM-compatible computer using MS-DOS. For a Mac version, use Wildtrak.
The programs will write to, and read from, temporary files created on the default drive. The analyses are performed most quickly if the programs are called up from a hard disk, where the data files are also stored.
Data should be contained in ASCII files, one file per animal with co-ordinates in sequential order. Each data line should contain the following variables: time (hrs and minutes or decimal hours), date (with 4 digits for the year), x- and y-co-ordinates (integers), activity (optional). For nocturnal tracking data, remember that the date changes at 00:00 hrs. These variables can be positioned in any order along the line, but they must occupy the same column positions throughout the file. This is because the programs identify the variables on the basis of the columns they occupy. The first time you run one of the programs you will be able to create a separate file of these column positions. This can then be called up on subsequent runs of this or the other programs.
Try running the programs on the sample data (ANIMAL01.TXT and ANIMAL02.TXT with COL.DEF to identify column positions). Just type the name of the program you want to use and then press the enter key ("DRIFT<enter>" etc.). The programs are self-explanatory. When running DRIFT on ANIMAL02.TXT, look at weekly, monthly, or yearly changes in range size and location (and the relation of cumulative fix total to range size) using 5x5m grid-cells with the option of influences and a 15-mins independence interval. When running dynamic on these two sample files, use a time-block of 15 mins and a critical separation distance of 10m.
The programs will ask you to specify an independence interval. If you give 10 mins (say), then the selection will be done for you so that only fixes spaced apart by at least 10 mins are taken (for example, skipping every other fix where you have 5-min intervals between fixes).
The main function of these programs is to help you explore your data and to give numeric values to relationships between individuals that you already know about in a qualitative way.
Beware of apparent dynamic interaction resulting from two animals regularly coming and going at similar times from the same or different sleeping positions. Use only active fixes or data from the middle of the night to get around this problem.
Note also that instantaneous (or nearly so) fixes may be easier to obtain when the pair of individuals are close together than when they are far apart. If so, you could end up with a greater proportion of paired fixes at close separation than is representative of the actual time they spend together, and the extent of positive dynamic interaction will be over-estimated.
The correlation coefficient for static interaction is best used in comparisons between pairs of animals. If you want to compare the concordance in utilisation distributions of a pair to random expectation, then it might be useful to simulate model territories of similar size and overlap but containing random fixes. Several runs of the model data through the static program will give a mean + confidence intervals for the correlation coefficient under the null hypothesis of random utilisation (see for example Taber, A.B. et al. 1994. Mammalia, 58: 61-71; Doncaster, C.P. & Macdonald, D.W. 1997. J. Zool. Lond., 241: 73-87).
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