What are the different communities in an Ecosystem?

The textbook for your class probably has the specific answer they are looking for. Otherwise "communities" tend to refer to the various different groups of organisms in an ecosystem, like pond flora/fauna, stream flora/fauna, field critters, etc.

My daughter studied ecosystems in the 4th grade so I did learn alot about them last year. I do not remember the use of the word communities, but I would guess it like roborne explained.