A simple simulation model of dispersal of animals among units of discrete habitats

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Abstract
A simple simulation model of dispersal of animals among units of discrete habitats has been constructed. This model outputs the numbers of animals reaching each of twenty-five “habitats” at preselected loci in a grid under a variety of operating conditions. These conditions consist of variables controlling directionality, velocity and mortality during dispersal. The relationship between numbers of animals reaching a particular site and the distance of that site from the starting point was investigated. Similarly, the effects of directionality (as determined by the variance of the normal distribution used to assign directions of movement), mortality and velocity on the overall rate of success were studied. A negative exponential-type drop off in numbers of animals reaching a site was predicted with increasing distance from the starting point. The relationship between percent success, directionality and rate of mortality was predicted to be curvilinear; the percentage declining with decreased directionality and increased mortality. A positive linear relationship was indicated between the spatial displacement per iteration used and percent success. Wherever possible the assumptions and predictions of the model are compared with available data. The assumptions concerning initial and subsequent directions of movement were found to be borne out by the data examined as were the results showing the relationship between numbers at each site and distance from starting point. The other results of the simulations were more difficult to compare with available data and some of these remain to be tested. The advantages and disadvantages of the model and the prospects for its expansion are discussed. It is concluded that the model is simplistic but that this gives it a generality and versatility which make it a useful tool for further thinking and investigation on the process of dispersal.