Habitat segregation between sympatric Tibetan argali Ovis ammon hodgsoni and blue sheep Pseudois nayaur in the Indian Trans-Himalaya

Abstract

Tibetan argali Ovis ammon hodgsoni and blue sheep Pseudois nayaur have almost completely overlapping distributions encompassing most of the Tibetan plateau and its margins. Such a sympatric distribution of related species with similar ecological requirements implies that there is some degree of resource partitioning. This may be accomplished on the basis of habitat and/or diet separation. This study evaluated such ecological separation on the basis of physical habitat partitioning by these two sympatric ungulates in Hemis High Altitude National Park, Ladakh, India, in an area where the argali established a small new population in 1978. Such separation was tested for on the basis of expected difference between the species in their proximity to cliffs, associated with species-specific anti-predator behaviour. Tibetan argali selected habitats away from cliffs while blue sheep selected habitats close to cliffs. Blue sheep also selected steep slopes whereas argali selected gentle slopes. The two species did not differ in their use of habitats in terms of elevation. They did, however, differ in their use of plant communities; blue sheep selected sub-shrub and grass-dominated communities whilst argali selected forb-dominated communities. We suggest that the two species coexist in this site as a result of the differential use of habitat associated with their species-specific anti-predator strategies.