SYSTEMATICS, SPECIATION AND BIOGEOGRAPHY OF THE DWARF CHAMELEONS (BROOKESIA, REPTILIA, SQUAMATA, CHAMAELEONTIDAE) OF NORTHERN MADAGASCAR

Brookesia dwarf chameleons, endemic to Madagascar, were surveyed at th e following localities in northern Madagascar (north of 16 degrees S): Montagne d'Ambre, Ankarana, Manongarivo, Tsaratanana, Marojejy and Ma soala. A total of 15 species occur in this region. Six new species are described and five new synonyms are identified. The genus Brookesia, the most speciose chamaeleontid genus in Madagascar, contains 23 speci es. Almost all the northern Brookesia species are restricted to rainfo rest and occupy a relatively narrow elevational range. Although the no rthern rainforests represent just one-third of the total rainforest an d about 5% of the total island area, 65% of the Brookesia species occu r in this region, and 52% are endemic to the northern rainforest. Five new biogeographic regions of the northern rainforest are identified b ased on centres of Brookesia endemicity: Montagne d'Ambre, Northwest, Tsaratanana, Northeast and East. Speciation is thought to have been fa cilitated in the north through geographic isolation, with the Tsaratan ana mountain range and the dry forests south of Montagne d'Ambre formi ng barriers to dispersal, and the Tsaratanana mountains acting as a ce ntre of isolation. The fragmented distribution of several Brookesia sp ecies of low altitude rainforest suggests a period in Madagascar's his tory when the climate was wetter and low altitude rainforest much more widespread.