Population biology is the study of the factors determining the size and distribution of a population, as well as the ways in which populations change over time. The discipline of population biology dates back to the 1960s, when researchers merged aspects of population ecology with aspects of population genetics. It employs a traditional empirical approach which consists of observation of the numbers of individuals in a population and the variation in those numbers over time and space, and the measurement of physical (abiotic) factors and the living (biotic) factors that may affect population numbers.

Given optimum conditions, the populations of most organisms grow at a constant rate of increase, doubling in size at regular intervals, which is known as exponential growth. Exponential population growth is explosive but it is usually opposed by factors that reduce numbers, such as disease, predation, or harsh climates. The result is...