In genetics a population is a group of interbreeding individuals of the same species, which is isolated from other groups. In population ecology a population is a group of individuals of the same species inhabiting the same area. Interbreeding is seldom considered in ecological studies of populations. The exceptions are studies in population genetics and evolutionary ecology. Populations can be defined at various spatial scales.
Local populations can occupy very small habitat patches like a puddle.
A set of local populations connected by dispersing individuals is called a metapopulation. Populations can be considered at a scale of regions, islands, continents or seas. Even the entire species can be viewed as a population. Populations differ in their stability. Some of them are stable for thousands of years.