What Can We Learn about Seed Dispersal from Seed Trap Experiments at Fruiting Trees? Efficiency of Dispersal Traits



Abstract A new index that measures efficiency of dispersal traits is proposed to replace the “removal rate.” Escape from the mother plant is essential for survival of seeds. The percentage of escaped seed is therefore a good indicator of the efficiency of dispersal. However, seed trap experiments measure only an apparent rate of escaped seed (AES), because of contamination by seeds from other conspecific trees. If we assume that as many seeds of the experimental tree are carried to conspecific trees as travel in the reverse direction, AES is a good estimate of seeds escaped from both the mother and conspecific fruiting trees. This may be called the rate of effective escaped seeds (EES), because the seeds carried to conspecific trees have no more meaning for survival than those defecated beneath the mother tree. As an example, two fruiting traits, synchronous ripening and extended ripening, were compared for their efficiencies in terms of AES(? EES) at an urban botanical garden for two seasons. In the extended ripening species, about 80 percent of seeds were successfully dispersed away from the parent plant or conspecific plants for both seasons, but the percentages fluctuated, between 60 and 86, in the synchronous one.