Distribution and deployment of Presbytis melalophos group in Sumatera, Indonesia

Pelage color and pattern, facial markings, cranial morphology, and vocalization have been studied comparatively in the Presbytis melalophos group in Sumatera. Pelage coloration of fetuses and neonates were described for P. melalophos and P. femoralis. Based on this study, three species -P. thomasi, P. melalophos, and P. femoralis - are recognized. Using field data that have been gathered since 1981, the distribution of these three species has been mapped. The resultant map reveals that no sympatry is known and that rivers form the interspecific boundaries. However, rivers apparently are not barriers to the dispersal of species in this group. Instead, distributions appear to be limited ecologically, by competitive exclusion. Historically, it appears that the ancestral stock initially dispersed throughout this area, then the P. melalophos stock split from the P. thomasi-P. femoralis stock, the P. thomasi stock split from the P. femoralis stock, and, finally, the P. femoralis stock dispersed to eastern Sumatera. It appears unlikely that the centrifugal speciation hypothesis based on the principle of metachromism applies to deployment of the P. melalophos group.