Biological dispersal
Biological dispersal refers to those processes by which a species maintains or expands the distribution of a population. Dispersal implies movement—movement away from an existing population (population expansion) or away from the parent organisms (population maintenance). In the latter case, dispersal may simply involve replacement of the parent generation by the new generation, with only minor changes in geographic area occupied. In either case, dispersal is important because new life must replace old, and the two generations cannot easily occupy the same physical space during the transition. More significantly, dispersal enables the species population to occupy much of the available habitat, thereby maximizing resources in its favor and providing a hedge against local adverse events.
In most cases, organisms (plants and especially sedentary animals) have evolved adaptations for dispersal that take advantage of various forms of kinetic energy occurring naturally in the environment: water flow, wind, falling caused by gravity.