Species distributions and the diversity of animal and plant communities are shaped by a complex interplay of geological, abiotic, and biotic factors. Species that inhabit a biome or a wider biogeographic realm are not found throughout its extent but occur within relatively smaller spatial scales. This is because species are limited, firstly, by how far and wide they can disperse, and secondly, by their tolerance to the abiotic environment, the presence/absence of resources, the abundance of their predators and parasites, and by other competing species. Of all these factors, the abiotic environment and competition have received considerable support based on empirical evidence. Linking changes in diversity across communities to proxies of ecological niches and evolutionary histories allow community ecologists and biogeographers to decipher the drivers of community assembly.
Mountains are excellent sites for studying the drivers of species distributions and the diversity of communities. Temperature decreases consistently with increasing elevation. Correspondingly, species diversity changes idiosyncratically across taxa with elevation. Different species occupy different elevational zones and some species are often restricted to very narrow elevational ranges. As a result, adjacent elevational zones may contain a mix of species with similar/dissimilar ecological niches or evolutionary histories. Therefore, an elevational gradient inherently comprises an abiotic gradient and a gradient of changing species interactions – a phenomenon that has fascinated biologists since the time of Alexander von Humboldt. However, studies on the patterns of species distributions along mountains are biased towards easily observable taxa such as birds and plants. Additionally, many mountain ranges, especially in the Global South, remain unsampled despite supporting high biodiversity.
Alarmingly, mountains are also under immense threat from anthropogenic stressors. Most notable among the stressors is climate change which is causing species to shift their elevational distributions. Without knowing about the current state of biodiversity on mountains, it is hard to predict how different taxa will respond to future climate change. Therefore, taxon-specific syntheses of the state of mountain biodiversity may help in identifying species and regions that need prioritisation in research and/or conservation.
This thesis is an exploration of the patterns of the diversity of bats and the conservation status of bats on mountains at local and global scales, using a combination of data collected in the field (first and second chapters) and those gathered from the public domain (third chapter). In the first chapter, I investigated the change in taxonomic, functional, and phylogenetic diversity across an elevational gradient in the Himalaya. I found that species richness decreases with elevation, functional diversity decreases significantly only at the highest elevation, and phylogenetic diversity remained unchanged across the elevational gradient. In the second chapter, in order to understand the mechanisms that sustain the diversity, I investigated trophic niche partitioning among bat species in areas of high vs. low diversity using stable carbon and nitrogen isotopes. My results demonstrated that species in low elevation assemblage with the highest species richness show high niche overlap, whereas, those at the high elevation assemblage showed low niche overlap perhaps to avoid competition in a harsh, resource-poor landscape. In the third chapter, I reviewed the global distribution and conservation status of bats on mountains using data available via the International Union for Conservation of Nature (IUCN). My analyses identified 148 mountain specialists and eight high elevation specialists, a majority of which are found in the Oriental biogeographic realm. These mountain specialist and high elevation specialist species are proportionally more data deficient than lowland bat species.
Overall, the thesis fills some important knowledge gaps by adding a taxonomic and a geographical perspective to the knowledge on community ecology and biogeography. It also highlights crucial knowledge gaps in our understanding of bats found in mountains and helps identify species of conservation and research interest.
