Answer
A population is a group of the same species living together in the same geographic location. A community is several groups of different species all living in the same geographic and interacting with each other. An ecosystem is all populations of a community, and the physical environment they live in, interacting.
In summary: a population is one species group. Many populations are a community. A community and the physical environment it lives in is an ecosystem.
Work Step by Step
A population is one group of a species. Many populations in a location is a community. A community and their environment is an ecosystem.