So, communitites are part of an ecosystem--the biotic part, while the ecosystem is the sum of biotic (living) and abiotic (nonliving) components.
(communitites; are; part of an ecosystem) (the ecosystem; is; the sum of biotic (living) and abiotic (nonliving) components)
communitites the ecosystem
are is
part of an ecosystem
the sum of biotic (living) and abiotic (nonliving) components