Final answer:
Population changes are influenced by demography, which includes fertility, mortality, and migration, as well as density-dependent and density-independent factors from nature.
Step-by-step explanation:
Populations change in size due to a variety of factors that can all impact the rate at which a population grows or declines. Demography, the statistical study of populations, analyzes changes in population composition and size. Key factors that cause population changes include fertility, mortality, and migration. These demographic variables impact not only the number of individuals within a population but also the composition and distribution of the population across different geographic areas.
Nature also contributes to the regulation of population growth through density-dependent and density-independent factors. Density-dependent factors are influenced by population density and include aspects like competition for resources, which can affect both growth rate and mortality. In contrast, density-independent factors impact mortality in a population regardless of its density, such as natural disasters or seasonal changes.
Demographic theories like the Malthusian theory and demographic transition theory help sociologists and biologists understand and predict population dynamics, including growth patterns and potential outcomes concerning the planet's natural resources.