There are several theories about immigration.

The theory of migration is population migration and species migration.

Population migration refers to the process of people moving from one place to another. Population migration can be short-term, such as travel and business travel, or long-term, such as immigration and relocation. Population migration will have an impact on both the place of immigration and the place of emigration, such as increasing labor force, promoting economic development and improving living environment.

Species migration refers to the process of biological population moving from one place to another. Species migration can be short distance, such as bird migration, or long distance, such as the spread of marine life. Species migration is of great significance to the balance of ecosystem and biodiversity. Technology migration refers to the process of transferring a technology from the place of invention to the place of application. Technology transfer can be domestic or international.

Characteristics of migration

1, migration is directional. In the process of migration, organisms usually migrate from places with poor living environment to places with good living environment. This migration helps organisms to find a more suitable environment for survival and reproduction, thus improving the survival rate and reproductive success rate.

2. Migration is seasonal. The migration activities of many creatures are affected by seasonal changes, such as migratory birds moving south in winter and north in summer. Seasonal migration helps organisms avoid unfavorable seasons and choose suitable seasons for breeding and foraging.

3. Migration is a long distance. The distance of biological migration is short and long, ranging from a few kilometers short to thousands of kilometers long. The length of migration distance depends on the habits of biological species, the change of living environment and the purpose of migration.

4. Migration is also regular. The migration activities of many creatures have certain rules, such as regular migration every year. This regular migration contributes to the spatial distribution of biological population and the utilization of resources.