Aquatic ecology and Biodiversity

Unit 3- Population ecology

3.14. Dispersal
Dispersal is “a phenomenon where the individuals (not all) of a population move into or out of the population”.
Dispersal is movement of individuals or their offspring into or out of an area. Dispersal allows individuals to colonize new areas. Dispersal, along with birth and death rates, regulates population size, and plays an important role in evolution through mixing of genes between populations. Dispersal is accomplished through immigration (movement into a population), emigration (movement out of a population) or migration (frequent movement into or out of a population area).

Migration : It is a periodic movement of animals from one place to another and back for breeding, feeding, and shelter - Fishes, birds, mammals etc.
• Catadromus – Fresh water to sea for spawning. Eg: Eel-Anguilla sp.
• Anadromous – Sea to fresh water for breeding. Eg: Salmons. Trouts etc.

Emigration: It is outward migration from a population. It is one way migration and migrant
never return – commit suicide. It is due to food scarcity and over population. Eg: Lemming population (Small rodents)

Immigration : It is inward migration, one way migration. It changes the structure of a stable population.