The term "population" is used to describe organisms of a single species that live together in the same area. Populations combine to form communities, and communities merge with abiotic factors to create an ecosystem.
A population of animals is capable of breeding due to their close proximity and genetic compatibility. The combined genes from each parent dictate the characteristics of the offspring. Favorable genes that help the animal survive increase in frequency, while less desirable genes appear less frequently over time.
Populations interact with other populations to form food chains and food networks. Each population serves a role in the ecosystem, such as decomposing dead organisms or preying on species and helping control its numbers.