Which factor is NOT considered a major determinant of a population's growth?

A population's growth is influenced by several ecological factors that can either promote or inhibit its size over time. The option identified as not being a major determinant of a population's growth is migration. While migration does play a role in changing the dynamics of population size by bringing in new individuals or allowing some to leave, it is often considered a secondary factor compared to others, such as predation, pollution, and available resources.

Predation directly affects the number of individuals in a prey population, often leading to fluctuations in their numbers based on predator presence and hunting efficiency. Pollution can have drastic effects on population health and reproduction, limiting growth potential due to declining habitat quality or direct impacts on individual organisms. Available resources, such as food, water, and shelter, are critical for sustaining population growth, as they directly influence birth rates and survival rates.

In contrast, migration typically acts as a response to other environmental factors. It reflects movements of individuals rather than directly contributing to changes in population growth rates. Therefore, while migration can be important in ecological studies, it is not as direct a determinant of growth as the other factors listed.