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 after they leave the parent plant, and then we examine the relative influences 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 movements. Although less studied, Phase Il dispersal is more likely to account for the patterning of plants in communities and ecosystems and is the focus of this review. Abiotic factors influence Phase II dispersal-the distance and type of movement depend on seed morphology, surface attributes, and the nature of the physical forces. Biotic factors (animals) move seeds to new sites passively either on body surfaces or by ingestion, or actively by consuming fruits or hoarding seeds. Animals also influence the movements of seeds through digging and burrowing activities. Arrival at microsites suitable for germination and establishment is critical and is affected not only by abiotic and biotic factors but also by seed morphology and germination responses. We emphasize that seed banks are much more dynamic than they are usually portrayed. Although 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 conservation efforts and for the control of alien species in all biomes.