On the Dispersal of Drosophila

The data on the dispersion of Drosophila pseudoobscura reported by Dobzhansky and Wright (1943) have been reexamined; the log of the number of flies recaptured at various distances from the point of release (both for capture of individual days following release and, for practical purposes, the cumulative captures of all days) decreases linearly with the square root of distance. Crowding seems to cause an artifically rapid dispersal of the released flies. A theoretical reconstruction of the composition of a single, highly localized collection of flies reveals that as many as one-quarter of all flies in such a collection may have emerged from pupae within 25 meters of the collection site. Available data suggest that D. melanogaster, D. willisioni, and D. funebris are much more restricted in their dispersion; 60% to 80 % of individuals of these species collected at one spot may have points of origin lying within a radius of 25 meters.