Mechanistic Models for the Seed Shadows of Wind-Dispersed Plants

Abstract

I present four models for the seed shadow of an individual plant. Of these, two (the tilted-plume and Godson models) are already extant in the literature and take the form of partial differential equations based on considerations of the fluxes of suspended seeds. The other two are original and are based on a stochastic approach to modeling the trajectories of individual seeds, obtaining the seed shadow as the probability distribution of the dispersal distances of a large number of individual seeds. Some numerical and analytical results are presented for these four models, particularly concerning the dependence of mean and modal dispersal distances on seed settling velocity and plant height. I also present the results of a simple experiment on the effects of seed-release height and ground-surface type on dispersal distances. Both factors, as well as their interaction, are statistically significant. Other microclimate variables were measured, allowing me to obtain estimates of the parameters of the four seed-shadow models presented previously. The predictions of the four models based on these independently obtained parameter estimates are compared with the data. Mechanistic models of seed dispersal can provide precise descriptions of seed shadows, which promise to provide further insights into the evolution of dispersal ability and its role in population dynamics.