Presbytis species sympatry in Borneo versus allopatry in Sumatra: an interpretation

Abstract

A review of the diversity of opinion on the number of Sumatran species recognizable for the genus Presbytis sensu stricto, indicates that an over-reliance on sympatry as a criterion for specific status, produces an underestimation of the species number in Sumatra, compared with Borneo. It is advocated that, for reasons of consistency, geographic variation in pelage colour must retain senior taxonomic status over geographic variation in adult male loud vocalization, but that the latter character corroborates the conspecificity rather than convergence of the Bornean and Sumatran grey-backed species, Presbytis comata. It is inferred that Presbytis potenziani was the sole species of its genus to survive an early stadial of the most recent glaciation, and that Presbytis comata derived from it during the subsequent interstadial and was approximately restricted to its modern distribution by a milder second stadial. The remaining species of the genus have derived from Presbytis comata since the glaciation. Allopatry in Sumatra is attributed to the northern part of the island forming a more active post-glacial dispersal centre than the comparable area in north Borneo. Only one Bornean species, Presbytis frontata has derived from Presbytis comata in Borneo. The other two, Presbytis femoralis and Presbytis rubicunda, had their origins in Sumatra.