However, depending on the context, you could consider these options:
General opposites:
* Chaos: The opposite of a balanced, interconnected system.
* Isolation: The opposite of a system where organisms interact and depend on each other.
* Disorder: The opposite of an organized system.
More specific opposites:
* Artificial environment: An environment created by humans, not naturally occurring.
* Unnatural environment: An environment altered significantly by human activity, not a natural system.
* Simple system: A system with fewer components and interactions than a complex ecosystem.
The best opposite word for "ecosystem" will depend on the specific context in which you are using it.