ABSTRACT
Dispersal has two functions in species diversification: one is in determining the range of a species and the other is in bringing about gene flow within and among populations. The seed-dispersal ability of a plant species significantly influences the regional distribution of plants. The case of pantropical plants with sea-drifted seeds (PPSS) is a remarkable example of species having wide distributional ranges. The wide distributions of these PPSS species have been explained largely by their high dispersal potential. Only a few plant species can establish and thrive with pantropical distributions like PPSS, because traveling by sea and living in coastal habitats are extremely difficult for most plants. The wider the distribution area resulting from sea-drifted seed dispersal, the greater the genetic heterogeneity among populations. Coastal vegetation has been repeatedly exposed to natural disturbances such as tsunamis, sea storms, tidal surges and sea-level rises. Local populations of PPSS can be easily damaged and may even disappear from strong natural disturbances.
