The ecosystem is the ecological structural and functional unit in which living species interact with one another and with their environment.
In biology, a population is the total number of organisms belonging to the same group or species that exist in the same geographical area and can interbreed.
In biology, a community, sometimes known as a biological community, is a group of species that interact in a common environment.
All five levels of organisation in an ecosystem are listed in increasing order of size – from tiny to large – according to the five levels of organisation.
Organism → Population → Community → Ecosystem → Biosphere
The community is bigger than the population, but it's not as big as an ecosystem.