Ecology, Genetics and Conservation of Himalayan Brown Bears [Ecologie, génétique et conservation des ours bruns de l'Himalaya].

Résumé

Asian bears are greatly threatened due to the impact of human activities, yet there is a critical lack of knowledge about their status and requirements for survival, which complicates conservation efforts. This study documents ecological requirements, genetic structure and life history of Himalayan brown bears (Ursus arctos), which have fragmented and mostly declining populations in South and Central Asia. Presently, brown bears in Pakistan are distributed over three main mountain ranges (Himalaya, Karakoram, and Hindu Kush), probably in seven populations. All of these populations are small and declining. Deosai National Park (DNP) supports the largest and most likely the only growing population (5% annual growth, based on the 14-years census). The genetic and field methods provided a population estimate of 40-50 individuals in DNP. The fecal DNA analysis revealed that the level of nuclear genetic diversity of the Deosai population was globally lower than brown bear populations that are considered to have a good conservation status, such as in Scandinavia or North America. However, in spite of the presence of a bottleneck genetic signature, the Deosai population has a moderate level of genetic diversity and is not at immediate risk of inbreeding depression. The DNP population has an exchange of individuals with neighboring populations in Pakistan and India, which is maintaining its genetic health. The analysis of the diet of brown bears in DNP, combing classical and molecular genetic techniques, indicated a great diversity in food species. They consumed over 50 plant species, invertebrates, ungulates, and several rodents. Eight plant families; Poaceae,Polygonaceae, Cyperaceae, Apiaceae, Asteraceae, Caryophyllaceae, Lamiaceae, and Rubiaceae were commonly eaten. However, graminoids made up the bulk of the diet. Golden marmots (Marmota caudata) comprised the major mammalian biomass in the park, and were also the main meat source for bears. Animal matter, comprising 36% of the dietary content, contributed half of the digestible energy, due to its higher nutritious value. Male brown bears were more carnivorous than females, probably because of their larger size, which requires higher energy and also makes them more efficient in capturing marmots. The habitat analysis (by Ecological Niche Factor Analysis) revealed that bears avoided higher elevations and steeper slopes, and showed a higher preference for more productive parts of the park (marshy, grassy, and stony vegetation types). The marshy vegetation was the most preferred habitat, probably due to its highest forage production and highest density of golden marmots. Brown bears tolerated human structures, such as roads and camps, but strongly avoided grazing areas with higher livestock density. We followed recognizable individuals from 1993 through 2006, and documented an extremely low reproductive rate in the Deosai population, due to late age of first reproduction (8.25 years), a long reproductive interval (5.7 years), and a small litter size (1.33). The family association (4.2 years) is the longest ever reported for brown bears and might have contributed to relatively higher survival of young. The reproductive rate of the Deosai population was the lowest yet documented for any brown bear population. The estimated digestible energy available to brown bears in Deosai National Park was also the lowest yet documented for any brown bear population, due to the lack of fruits and relatively lower meat content in the diet. The poor quality of the diet and high cost of metabolism in a high altitude environment probably explain the very low reproductive potential of this population. The combination of poor intrinsic growth potential and exchange of individuals suggest that the observed population growth was a product of both reproduction and immigration. The recovery of the brown bear population in Deosai is significant, because the species is declining throughout most of its range in