Ecosystems do not have to be completely the same throughout, they can have regional variations. So an ecosystem within an ecosystem is much like a neighborhood within a city.
An Eco-system isn't something that is alive. It is something where living species can depend on each other.An Eco-system can not live inside another Eco-system
An ecosystem is a community of...
parts of ecosystems may be in another ecosystem, like say a evergreen pine tree was covered in water , or the land was flooded, that would be a part of land-based ecosystem in an aquatic ecosystem.