(Adds Warfalla tribe rejects Gaddafi)
Feb 22 (Reuters) - Muammar Gaddafi, facing an unprecedented popular revolt, has stayed in power for four decades in part because of his adept manipulation of tribes, centres of power in what remains a conservative, sparsely-populated desert country.
Historians say the veteran ruler has used economic privileges, marital alliances and the threat of force to build ties to tribes commanding varying degrees of loyalty among most of the six million population.
Gaddafi's own tribe, the Al-Gaddadfa, one of more than 20 tribes in the country, is based around the Mediterranean coastal city of Syrte in the northern middle of the country's territory.
Despite its small size, its location - in the heart of the Syrte basin rich in oil - gave the tribe pre-eminence and led to claims by its descendents that they trace their lineage directly from Prophet Mohammad, some historians say.
The tribal view of politics in Libya is heavily marked by the violence of the country's modern history, especially during Italian colonisation from 1912-43, which made many elders generally wary of the concept of a central authority.
Gaddafi managed to pacify the tribes, or at least obtain their cooperation, mainly through crushing violence or the fear of it, exemption from the payment of taxes for the majority of those tribes that rely on pastoral activities, and alliances through marriages or economic privileges.
Gaddafi focused his effort to build alliances with tribes in the Tripolitania region, which in the Ghadamis basin holds some of the country's most significant oil deposits.
Al-Zuwayya tribe, whose leader threatened on Sunday to cut oil exports if the violence is not stopped, is located in both the Cyrenaica and Al-Kufra regions whose joint oil production accounts for little compared to the rest of the country.
On Feb. 20, Akram Al-Warfalli, a leading figure in the Warfalla tribe, one of Libya's biggest, told Al Jazeera: "We tell the brother (Gaddafi), well he's no longer a brother, we tell him to leave the country."
A source in the Warfalla sent a message to the same effect in a statement to Reuters on Feb. 21.
Following are the main tribes in Libya.
TRIPOLITANIA REGION: Warfalla, Awlad Busayf, Al-Zintan, Al-Rijban
CYRENAICA: Al-Awagir, Al-Abaydat, Drasa, Al-Barasa, Al-Fawakhir, Al-Zuwayya, Al-Majabra
SYRTE-GIBLAH: Al-Gaddadfa, Al-Magarha, Al-Magharba, Al-Riyyah, Al-Haraba, Al-Zuwaid, Al-Guwaid
FEZZAN: Al-Hutman, Al-Hassawna, Tibbu, Tuareg
AL-KUFRA: Al-Zuwayya, Tibbu (Writing by Souhail Karam; Editing by Jon Hemming)