Quite true.

I would think one might classify our bodies as ecosystems.

Battlefields as well I suppose, as many of those viruses are probably invading many of those bacteria. Just happened to see a show that was talking about how viruses (bacteriophages specifically, viruses that attack bacteria) are being researched as the next replacement for all those fast becoming ineffective antibiotics against bacteria that have become resistant. Viruses are the latest domesticated ..... animal??.