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The distribution of the Nilgiri langur (Semnopithecus johnii) a threatened colobine endemic to the southern Western Ghats and the hanuman langur (Semnopithecus priam) an endemic to south India and Srilanka abuts each other in some parts of their common boundary i.e. they show a parapatric distribution in the southern Western Ghats. There have been reports of hybridization between them in some areas. Natural hybridization has been reported between several primate species. However, studies that have systematically documented extent of parapatry and zones of hybridization of primates are very limited. Co-occurrence and importance of natural hybridization in primates is only now being recognised. This project is part of a larger study on the extent of parapatry between these langur species in the southern Western Ghats, which aims to identify regions of possible hybridization and understand the influence of specific environmental and habitat factors on the distribution pattern of these primate species. Specifically, this project supported the field work in the Anamalai hills. Given the ambiguity in the langur taxonomy, data on distribution, parapatry and zones of hybridization from this study will be of considerable importance.
- To what extent are the langurs distributed parapatrically in the southern Western Ghats?
- Do specific environmental and habitat factors influence this pattern of distribution?
- Detection/non-detection data, collected systematically, was used in an occupancy framework to model the site-level probability of occupancy of the two species, species-interaction, co-occurrence and identify factors that influence their occupancy. Our results indicate that the occupancy of Nilgiri Langur (NL) was higher than Hanuman Langur (HL) in the study area.
- The two species had contrasting habitat preferences: NL preferred low aridity areas with closed canopy at high elevations while the HL preferred more arid areas at elevations lower than those occupied by the NL.
- The probability of co-occurrence is 0.29 indicating that the two species were parapatrically distributed.
- Maps of the probability of occurrence of the langurs indicate that in this landscape, the NL was found across a larger, more contiguous area compared to the HL, which occurred more on the disturbed eastern slopes of the Ghats. The revision in taxonomy, hybridization with NL, and smaller and fragmented occurrence in disturbed habitats, warrants a reassessment of the status of the HL.