In biology, a population is defined as a group of organisms belonging to the same species that occupies a specific geographic area at a given time. Population ecology is the study of the size, density, and distribution of these groups, and how these factors change over time. The dynamics of a population are governed by several key processes: birth rates, death rates, immigration (the entry of individuals from outside the area), and emigration (the exit of individuals). Changes in population size can lead to shifts in the species' interaction with its physical environment and other neighboring species, which forms the basis of understanding ecosystem stability and community structure.