Population biology is the study of organism populations as a whole. This branch of biology includes many different facets of biology, including evolution, statistics and genetics. It is used to understand how the population works together, the health of the population and how it grows and develops.
Rather than studying individuals, population biology takes a look at the whole population, be it the population as a whole or the local population. Evolution and genetics are an important part of this because isolated populations evolve and change different from one another, even when starting from the same place. Studying a population can help show scientists how abundant food is and which traits are most helpful for survival. For example, if one birthing season results in a lot of new young, then the food is plentiful and the population is thriving.
Population biology also looks at group dynamics to understand the social structure of the population, where the population fits into the larger group of populations in the area, and how the geography affects the population. In addition, invasive species are of particular importance to this division of biology. Because population geography is such a wide-reaching branch, it covers all forms of life, including both animals and plants.