Responses of Tibetan antelope population to environment changes during the Holocene

Tibetan antelope (Chiru, Pantholops hodgsonii), an endemic species of the Tibet Plateau, inhabits the open alpine and desert steppe areas ranging 3250 to 5500 m altitude. In the past decades, the antelope population has been significantly affected by human activities, including massive illegal hunting, followed by strict protection policies and establishments of natural reserves. Various techniques have been devoted to monitor antelope population changes and study their habitat, but these are limited to the past several decades and can only provide limited information on past changes in antelope population. We reconstructed antelope population changes during the Holocene using sediment cores at Lake Zonag, one of the most important calving grounds for Tibetan antelope. We measured the content of 24-ethyl-coprostanol and 24-ethyl-epicoprostanol, signature fecal sterols of herbivores, as a proxy for the antelope population. The fecal sterols captured the sudden decrease in antelope population due to illegal hunting in 1980s, as well as the recent recovery because of protection, giving us confidence in using fecal sterol as the proxy for population changes of the Tibetan antelope. The results show the antelope population in Lake Zonag region fluctuated significantly during the past 9000 years, with clearly low population at 5.1-4.5 and 4.1-3.7 ka. Fluctuation of antelope in the Lake Zonag catchment show strong response to environment changes during the Holocene. When the environment was relatively humid with dense vegetation cover, the antelope population increased, and vice versa. Over the past 400 years, the changes in the population size of Tibetan antelope have been affected by human activities.Our study was the first to identify the signature fecal sterols to represent the population changes of the Tibetan antelope. Understanding how the population size of Tibetan antelopes responded to environment changes in the past would provide scientific basis for long-term conservation policies for Tibetan antelopes.