Population ecology is the study of how populations — of plants, animals, and other organisms — change over ... and rates of infection increase with population density and can eventually ...

Populations ... population by changes in reproduction or survival. Wauters & Lens (1995) studied how food availability and density combine to limit red squirrel reproduction rates.

Population density (often abbreviated PD) is a compound measure that tells us roughly how many people live in an area of known size. It is commonly used to compare how 'built-up' two areas are.