Reptile tribes are proliferating across Tribe.net, but none of them have many members. It’s as much due to the fact that there aren’t many reptile keepers on that site — as opposed to tattooed polyamorist Burning Man devotees — as it is to fragmentation. Herewith a list of the tribes I know about; some don’t have a public URL and must be searched for from the site.
Social-networking sites rely on the network effect to take off — i.e., the more people are on it, the better it gets. So it’ll take a while before these tribes come into their own.