Final answer:
The term used to describe changes in population size over time is 'growth rate,' which encompasses the effects of birth, death, immigration, and emigration rates.
Step-by-step explanation:
The term used to describe the increase or decrease in the number of individuals in a population over time is growth rate. The population growth rate is determined by a formula that includes the birth rate (b), death rate (d), immigration rate (i), and emigration rate (e). The equation looks like this: r = (b + i) - (d + e), where a positive growth rate indicates a population is increasing, and a negative growth rate indicates a decrease. Immigration contributes to population growth by adding individuals, while emigration diminishes the population by subtracting individuals. Together, these factors are crucial in understanding demographic changes and managing population dynamics.
Emigration, which decreases the population size and growth, often occurs in conjunction with other factors like birth and death rates within a population. Hence, the combined effect of births, deaths, immigration, and emigration defines the population growth of an area.