Ecological correlates of explosive seed dispersal

Based on the constraints of the ballistic mechanism, we suggest that plants that utilize explosive dispersal are either maximizing ballistic distances or maximizing secondary dispersal (and thus are ballistically short-distance dispersers). Explosive seed dispersal of seven plant species was investigated in terms of factors contributing to the distance that seeds are thrown. As predicted, the long distance dispersers (4 species) showed more constancy in distance that seeds were thrown relative to the ballistically short-distance dispersers (3 species). The distribution of explosively dispersed seeds in terms of a resource for post-dispersal predators was evaluated by computer simulation. The results indicated that seed predation is unlikely to contribute to maximizing seed dispersal distance. A model for explosive seed dispersal was developed, based on the constraints of such dispersal. Long-distance dispersers were expected to use small, closely-spaced patches or to use large patches in which inbreeding depression or competition selects for maximal dispersal distances. Short-distance dispersers were expected to use small, widely-spaced patches where ballistic dispersal in itself is an inadequate means to disperse seeds, or to use large patches in which there is no premium for dispersal distance. Preliminary evidence supported the model.