Null Models and Dispersal Distributions: A Comment on an Article by Caley

[FIRST PARAGRAPH] In a recent article Caley (1991) outlined a null model for dispersal distributions against which he suggested empirical data should be compared. He first presented Waser's geometric model (Waser 1985), which can be derived as follows: Dispersing individuals move in a straight line from the natal site and settle in the first unoccupied site they encounter. If unoccupied sites occur independently at random with probability t as a result of turnover within the habitat, then the distribution of dispersal distances will follow a geometric distribution in which the probability of settling at distance i is given by p(i) = t(l - t)' for i = 0, 1,2,3,. . .

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