In Service Studio you can use process activities that are exposed by another eSpace, called, in this context, a Producer. Simply add these process activities as eSpace references of your eSpace, called, in this context, a Consumer eSpace.
How to Add a Process Activity Reference:
Once process activities are added as references, you can use them in your eSpace:
With process activities System actions to manage them.
Add/Remove eSpace References | Expose a Process Activity | Overview of System Actions