Mass Dispersal - Population Dispersal
A population is inherently dynamic in nature since individuals are always leaving or entering the populations. But such changes normally do not affect the size of a population. It is because emigrations balance immigrations or because gains and losses in terms of entry and exit of individuals are compensated by changes in natality and mortality. However, mass dispersal may bring out rapid changes in the population e.g., immigration may speed up population growth or in case of extreme reduction may prevent extinction.
Mass dispersal affects the balanced population in other ways also e.g., the immigration of large number of blue gill fishes into a pond already full of blue gill population may result in reduced growth of the fish population and also result in smaller average size of fishes due to environmental limitations. So even though the biomass density remains unchanged, the size of fishes may be much reduced affecting the fishing process.