Does anyone have reliable statistics (and barring that, reasonable anectdotal evidence) of the fraction of Kohanim, Levi'im, and Yisraelim in various Jewish communities today. By "communities" I don't necessarily mean geographic, but minhagic, like Chabad/Syrian/Litvak, etc.
Answer: Levites: 4%, Priests: 4%.
A scientific article which deals with the genetics of priests and Levites quotes a book from 1999 (not available for reading online) which estimates Levites and priests each at 4% of the general Jewish population. Source: http://www.sciencedirect.com/science/article/pii/S000292970763626X#bbib6 Referenced book: "The genetic origins of Old Testament priests", CE Renfrew, Editor, Population specific polymorphisms, Cambridge University Press, Cambridge, United Kingdom (1999), pp. 31–44
Djerba has almost all kohanim.