Hello Patric,
Glad you find my work useful in your PhD studies.
First, when you said social communities, do you just mean online communities? If that is the case, then I don't think they are separated. People belong to social networks through pre-established interpersonal relationships, but we also at the same time belong to many communities through common interests with other people.
You can take a look at a later article that I've written on this subject that explains why there are communities in social networks, but there are also social networks within communities. You can find the discussion in this blog article:
Cyber Anthropology: A Unified View of Communities and Social Networks
I don't know what your PhD thesis is on. But feel free to explore the rest of this series on Cyber Anthropology. I hope to see you on Lithosphere in the future.