When will plant morphology affect the shape of a seed dispersal "kernel"?

Most models of dispersal assume that plants are point sources. In reality, the scale in height over which seed sources are distributed is often of the same order as the scale in distance over which most individual seeds are d ispersed. But is this sufficient to affect the fundamental shapes of disper sal frequency distributions? Most published conclusions about the effects o f canopy structure on dispersal are subjective. A model is developed to exp lore the consequences of plant canopies for the shapes of whole-plant seed dispersal "kernels". The canopies were described by simple geometric shapes , while an empirical probability density function (PDF) was used for disper sal from a point source. It was found that the resulting whole-plant PDF fo r dispersal distance was almost invariably peaked, whereas the PDF for the density of seed rain las would be measured by pitfall traps) could either b e peaked or monotonic according to the canopy shape, position of seeds in t he canopy, and mean dispersal distance. The shapes of kernels from whole pl ants (distributed seed sources) can be very different from those derived fr om a point source under certain circumstances. (C) 2001 Academic Press.