Closing the seed dispersal loop_Benjamin C.Wang and Thomas B. Smith

Box 1. The seed dispersal cycle

It is important to distinguish between the process of seed dispersal, whereby seeds are moved from parent plants, and the seed dispersal cycle, which is a succession of processes (including the process of seed dispersal) whereby seeds produced by an adult plant are moved from the parent plant, germinate to seedlings, and recruit to adult plants,
influencing the fruit and seed availability of the next generation (Fig. I). Although seed dispersal is only one of the many processes in this cycle, we have chosen to call it the seed dispersal cycle to emphasize its role as a ‘demographic bridge’ linking the end of the reproductive cycle of adult plants with the establishment of their offspring [a]. Not all seeds are dispersed, and most dispersed seeds do not complete the seed dispersal cycle. However, the parents that produce seeds that successfully complete the cycle pass a disproportionate amount of their genes to the next generation and thus have a disproportionate influence on the vegetation composition of the succeeding generations.
Reference a Herrera, C.M. et al. (1994) Recruitment of a mast-fruiting, bird-dispersed
tree: bridging frugivore activity and seedling establishment. Ecol. Monogr. 64, 315–344

Fig. I. The two main approaches used to investigate animal-mediated seed dispersal
and its consequences: (1) Working forwards entails trying to follow the seed dispersal
process in the direction that it happens in nature (in the direction of the arrows). These
studies tend to focus on patterns and processes on the right side of Fig. I (given in red),
and many of them are classified as ‘seed dispersal studies’. A major hurdle has been
the difficulty of following the dispersers from parent plants to where they deposit
seeds to track the fates of those seeds. (2)Working backwards examines the
consequences of the seed dispersal process – seed, seedling, sapling, and adult plant
distribution – and tries to deduce the influence of seed dispersal in determining those
patterns. These studies focus on patterns and processes on the left side of Fig. I (given
in green), and many of them are studies of plant demography. Processes (given in
bold) generate the patterns (given in boxes) that can be measured.

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