Co-occurrence of ungulates in multi-species assemblages has fascinated ecologists because these species seemingly belong to the same guild – feeding on plants. Across large parts of the high mountains of Central Asia, ibex (Capra sibirica) and argali (Ovis ammon), both predominantly grazers, co-occur at local and regional scales. However, little is known about the ecological and anthropogenic factors that influence their spatial distribution, co-occurrence and habitat use. We examined factors affecting the distribution and co-occurrence of these two sympatric species in Tost Tosonbumba Nature Reserve in southern Mongolia using an occupancy modeling approach. Specifically, we used single species occupancy models to examine the influence of road density, livestock density, terrain ruggedness and elevation on occupancy of these two species separately. We then assessed how these two species influence each other’s distribution by using multi-species occupancymodels.
The model-averaged occupancy probabilities for ibex and argali were 0.64 0.3 SE and 0.44 0.2 SE, respectively. Terrain ruggedness positively influenced ibex distribution, while it negatively affected the occupancy of argali. We found limited evidence of relationship with factors associated with human disturbance. The species interaction factor, which indicates the level of co-occurrence, suggested that ibex and argali occurred independent of each other (φ =0.72 0.3 SE). Together, our results imply that there was limited co-occurrence between the two species and that this was largely driven by terrain ruggedness at the scale of the home range. These results suggest that topography plays an important role in enabling these two species to co-occur at the regional scale.
Chagsaldulam Odonjavkhlan, Post-Graduate, Program in Wildlife Biology and Conservation, Wildlife Conservation Society—India, National Centre for Biological Sciences, GKVK campus, Bangalore, Karnataka 560065, India.