Shapes of ballistic seed dispersal distributions: a comparison of Oxalis corniculata with a theoretical model.

Rezvani M, Cousens RD, Zaefarian F, Karimmojeni H & Robinson AP (2010). Shapes of ballistic seed dispersal distributions: a comparison of Oxalis corniculata with a theoretical model. Weed Research 50, 631–637. Summary A previously published ballistic dispersal model, based on fluid dynamics and a point source, predicts that the probability of dispersing a given distance has maxima close to the origin and at the greatest dispersal distance. We show that in plants of two taxa of Oxalis corniculata, the maximum probability of dispersal is very close to the parent, with a very minor secondary peak at intermediate distances. Using generalised additive mixed-effects modelling, we show that seed mass increases with distance from the parent and that distances dispersed by the two taxa differed. We conclude that although prediction from physical first principles is a justifiable goal, the complexity of plants as seed sources and in-flight obstacles means that predictions from very simple models may only rarely mimic reality. Until more realistic models for ballistic dispersal are developed, considerable care should be taken in the selection of dispersal functions in population models. Wherever possible, model structure should be supported by the collection of empirical data.