The goal of this project is to document the bird diversity of the Himalayas of north-east India, and to ask why more than twice as many species are present there than in the western Himalayas of India. A team of Indian scientists and students from the Wildlife Institute of India and the University of Chicago, USA, will work at several sites across the Himalayas, surveying densities and distributions of all species. In the laboratory, DNA sequencing methods will be used to evaluate the phylogenetic relationships among the species.
The study tackles a longstanding scientific problem: What are the historical and ecological causes of the difference in numbers of species between locations? It uses a novel approach to do this by studying patterns of decline in species numbers from east to west within many different genera of birds, and asking if the patterns are similar in each genus. The eastern Himalayas contain perhaps the second highest concentration of species in the world, but have been scarcely studied for various logistical reasons. Many animal and plant species remain to be discovered, including perhaps some new bird species. The work thus has broad conservation and educational significance.
One of the most basic of ecological questions asks: why are more species found in some places of the world than others? Over the past decade, advances in our knowledge of (1) the present day distribution of species and climate, (2) relationships among those species (from DNA sequences) and (3) earth’s history means that we can get much more rigorous answers to this question. In the work under review, we set out to collect these kinds of data to understand the cause of a more than two fold decline in the number of bird species breeding from the eastern Himalayas (where up to 600 species breeding in a 200 x 200km square) to the western Himalayas. The strength of the system is that >120 species are found in both locations, so we can study geographical variation within species, as well as assess the ecological attributes of those species with large ranges. As the conceptual basis to this study (i.e., intellectual merit), we argued that any understanding of causes of differences in species numbers between locations should begin by asking: what is it that sets the range limits of many species (i.e., what is it about the conditions beyond the range limit that prevent species from establishing there). This is particularly effective for the Himalayas, because species not only have geographical range limits, but also altitudinal ones, and these kinds of limits can be compared. First, on the basis of theoretical work, we noted that understanding of range limits almost certainly requires an understanding of resources (notably food) are responding to underlying climatic variables. The eastern Himalayas are particularly wet, and also warmer than the western Himalayas, and the big disparity in species numbers comes because certain climates are not experienced in the west at all; forest species below 2000 m decline massively from east to west, and ‘open’ species show no decline at all. However, many forest species do have ranges that extend from east to west. A critical question is whether those species with ranges that fail to go west are closely related to each other (and hence share some historical ‘constraint’), or whether close relatives often differ in range size. We find the latter is the case: many closely related groups contain one species that lives in higher, colder, drier climates, and another than lives lower down, and it is the higher up one that has a large geographical range. One of the more remarkable aspects of our work is how much we are learning the basic natural history, particularly of the little-known eastern Himalayas, which may have the second highest biodiversity in the world (after the northern Andes. By incorporating DNA analyses, we are finding multiple cryptic species in some groups (species which are very similar, but deeply genetically divergent). In this work, we are able to integrate both undergraduate and graduate students from both the US and India into both field and lab studies. The global perspective is needed to understand conservation issues, and to have much hope of conserving diversity in a region which is (1) amenable to conservation issues but (2) under considerable land and population pressure.
