Population growth rate is defined as the net rate of natality (birth rate) and mortality (death rate) in a given habitat over a period of time. It is a measure of how fast a population is increasing or decreasing in size. The population growth rate takes into account both the number of individuals in the population and the amount of time it takes for the population to change in size. It is an important concept in ecology, as it allows us to better understand how populations of different species interact with their environment and with each other.