A DAY IN THE LIFE OF A SEED - MOVEMENTS AND FATES OF SEEDS AND THEIR IMPLICATIONS FOR NATURAL AND MANAGED SYSTEMS

We develop a model that outlines the movements and fates of seeds afte r they leave the parent plant, and then we examine the relative influe nces of abiotic and biotic factors on those movements and fates. Phase I dispersal is movement of a seed from the parent to a surface, while Phase II dispersal includes subsequent horizontal or vertical movemen ts. Although less studied, Phase Il dispersal is more likely to accoun t for the patterning of plants in communities and ecosystems and is th e focus of this review. Abiotic factors influence Phase II dispersal-t he distance and type of movement depend on seed morphology, surface at tributes, and the nature of the physical forces. Biotic factors (anima ls) move seeds to new sites passively either on body surfaces or by in gestion, or actively by consuming fruits or hoarding seeds. Animals al so influence the movements of seeds through digging and burrowing acti vities. Arrival at microsites suitable for germination and establishme nt is critical and is affected not only by abiotic and biotic factors but also by seed morphology and germination responses. We emphasize th at seed banks are much more dynamic than they are usually portrayed. A lthough often poorly quantified, seed mortality can occur at any point in the model. Sufficient differences exist among biomes that certain generalizations can be made regarding seed dynamics. Knowledge of seed movements and fates is essential for ecosystem restoration and conser vation efforts and for the control of alien species in all biomes.