"Community" is term with a whole bunch of associations: collective, fuzzy boundaries, warm, social, perhaps a little suffocating, possibly a bit leftie.
"Tribe" has a different set of associations: also collective but harder boundaries, us against them, perhaps a little ruthless, possibly a bit atavistic.
Etienne Wenger and his many collaborators produced the theoretical work around communities of practice in learning & knowledge sharing. Meanwhile marketers & advertisers chose to identify* consumers based on the tribe they belonged to - trying to link abstract market segmentations to real social relations.
As online social spaces proliferate, we are hearing more about communities & tribes. But the more I hear these terms, the less I think they usefully describe what these new social groupings are. Few of our online groupings are either "tribes" or "communities" as most people would understand them. They are too loose, too ephemeral, too dynamic.
We don't have the words for what these things are yet. We have a language lag.
*And identity is important to both communities & tribes.