A population is a group of organisms belonging to the same species that live in the same area and interact with one another.
A community is all of the populations of different species that live in the same area and interact with one another. A community is composed of all of the biotic factors of an area.
An ecosystem includes the living organisms (all the populations) in an area and the non-living aspects of the environment. An ecosystem is made of the biotic and abiotic factors in an area.
