Final answer:
Population ecology studies how species' population sizes change over time and the factors influencing these changes within a specific environment.
Step-by-step explanation:
The study of population ecology focuses on understanding the number of individuals of one species in an area and how and why that number changes over time. This branch of ecology is concerned with factors such as birth rates, death rates, and migration patterns that influence population size and structure. Unlike organismal ecology, which looks at individual adaptations, or community ecology, which examines interactions among species, population ecology zeroes in on the dynamics of species populations within a specific environment.