| Abstract |
The loss of mammalian herbivores from grazing ecosystems has become a major concern,and efforts to stem such losses are stymied by lack of information on the proximate and ultimate factors influencing their distributions and diversity patterns. This research investigated the distribution, species-richness patterns and underlying mechanisms in mammalian herbivores of the Trans-Himalayan region of Ladakh, India. It adopted a multi-spatial approach to understand these issues in the little-known herbivore assemblage of the region. Since vegetation is the most important factor that determines the distribution of herbivores, first I researched the distribution and abundance patterns of vascular plants along an altitudinal gradient at different spatial scales. Both plant species-richness and aboveground biomass showed a hump-shaped relationship with altitude. Such a relationship in case of species-richness is expected, but it is contrary to my expectation of a negative linear relationship, in case of abundance. I relate this unexpected pattern to the limited precipitation and pervasive livestock grazing at lower altitudes in this dry alpine environment. I then investigated the biogeography of mammalian herbivores, and found that they form geographical groups on the basis of their evolutionary histories. Subsequently, I assessed the niche relationship between Asiatic ibex Capra ibex siberica and blue sheep Pseudois nayaur, the most common large herbivores in Ladakh, to see whether local level processes like competition generate spatial pattern of herbivore species-richness. The results showed that blue sheep constrains the distribution of ibex, which implies that competition amongst native species does play a role in structuring large herbivore assemblages in the region. Recognising the lack of information on large herbivores’ niche variation across assemblages, I also studied blue sheep’s niche width in relation to herbivore speciesrichness. It became apparent that the species’ niche varies across assemblages with different number of sympatric species, which could negatively influence the animal’s reproductive performance and population. Finally, I asked if the distributional range of the endangered Ladakh urial Ovis vignei vignei is constrained by the abundant blue sheep, and found that these two species associate randomly at large geographical scales, but cooccur at the landscape level as a result of local habitat-level resource partitioning. These results contribute towards understanding the mechanisms responsible for the formation and maintenance of large herbivore assemblages in the Trans-Himalaya and other mountainous regions of the world. |
