When is it possible for a population growth rate to be less than zero?

The population growth rate is calculated as the difference between the annual birth rate and the annual death rate. For example, if a population's birth rate is 5,000 and its annual death rate is 3,000, the difference is 2,000, meaning the population growth rate is 2000. If the annual death rate were to increase to 8,000, the difference would be -3,000, meaning the population growth rate would be negative.

Plagues can decimate a population and drastically increase the death rate, but they usually pass with time. Droughts, floods, and other natural disasters can kill members of a population directly, but they can also destroy their food supply, further increasing the death rate and potentially leading to a negative population growth rate. Common causes of negative growth rates would be disease, overpopulation, or lack of food and other necessary resources.

When emigration exceeds both immigration and birthrate in the case of humans, the population of a given nation may decline.

A population growth rate can be less than zero when the number of deaths exceeds the number of births, and there is also a net out-migration, meaning more people are leaving the population than entering it. This can occur due to factors such as low birth rates, high death rates, emigration, or a combination of these factors. When the population experiences negative growth, it results in a decrease in the total population size over time.