STOCHASTIC DISPERSAL PROCESSES IN PLANT-POPULATIONS

A dispersal model for airborne pollen based on assumptions about wind directionality, gravity, and a wind threshold at which pollen is taken by the wind is developed, using a three dimensional diffusion approxi mation. The bivariate probability distribution of pollen receipt by fl owers at the same height as the pollen source is derived. Gravity, ver tical random movements, and vegetation density turn out to have simila r effects on this distribution. Maximum likelihood methods far estimat ing the combined parameters from data with multiple point or continuou s pollen sources, and one or move plant varieties, are developed. Usin g an example data set from the literature, it is shown that our model gives a better fit than more traditional descriptive dispersal models of the form e(-arb). We also show that estimates of important properti es of the dispersal distribution, such as the variances, become consid erably smaller using our model than for the more traditional models. F inally, we discuss potential extensions and evolutionary implications of these types of models. (C) 1997 Academic Press.