Population Growth Rate
From the Encyclopedia of Earth
"The population growth rate measures how populations change in size over time. The units of population growth rate are individuals per time. Population size can only be changed by four factors. Births add new individuals to a population whereas deaths remove individuals from a population. Similarly, immigration into a population adds new individuals whereas emigration out of a population removes individuals. Population growth rates are positive when more individuals are added to a population than are removed, negative when more individuals are removed than are added, and are equal to zero when an equal number of individuals are added and removed. This population size is known as the carrying capacity and is the size beyond which no significant increase can occur due to limitations of some type, e.g., food, water, space, . . .".