ISSN 2075-1117, Russian Journal of Biological Invasions, 2015, Vol. 6, No. 1, pp. 37–50. © Pleiades Publishing, Ltd., 2015. Original Russian Text © A.P. Saveljev, S. Shar, A.E. Scopin, M. Otgonbaatar, V.A. Soloviev, N.I. Putincev, N. Lhamsuren, 2014, published in Rossiiskii Zhurnal Biologicheskikh Invasii, 2014, No. 4, pp. 55–75. 37 INTRODUCTION The study of adaptation processes of biological spe- cies which have been intentionally introduced by humans is a key task in the knowledge of evolution and functioning of biosystems at the beyond-organism lev- els. These issues were quite fairly included in the list of 100 fundamental ecological questions (Sutherland et al., 2013). The ecosystem of the Uvs Nuur Hollow is in the adjacent territories of Mongolia and Tuva (Russia) and is, according to an apt expression of Prof. V.V. Bugrovskii (1990), a typical “zone of life concentration” in the arid belt of Eurasia. In this respect, wetlands in the floodplain and delta of the Tes River are the most significant. Three introduced spe- cies of semiaquatic mammals (Eurasian beaver, musk- rat, and American mink) are historically new ecologi- cal factors for the Uvs Nuur Hollow with distinct tem- poral and territorial associations at the beginning of their impact. But the ecological role of alien species in this unique region, which was included in the UNESCO World Herritage List (UNESCO, 2003), was outside the scope of the researchers. Moreover, mammalogical publications describing the range of American mink in the territory of Mongolia did not indicate the presence of the species in the Uvs Nuur Hollow (Dawaa et al., 1977, 1983; Hoffmann, 1977; Sokolov and Orlov, 1980; Batsaikhan et al., 2010). The data on American mink in the region are fragmentary (Dulamceren et al., 1996) and are based on the results of the winter expedition of the Zhitkov Russian National Research Institute of Hunting and Animal Breeding at the end of January to the beginning of February 1991) (Saveljev and Shurygin, 1997). The aim of the study is to determine the modern distribution and to assess the role of three introduced Introduced Semiaquatic Mammals in the Uvs Nuur Hollow (Current Distribution and Ecological Vectors of Naturalization) A. P. Saveljev a , S. Shar b , A. E. Scopin a , M. Otgonbaatar c , V. A. Soloviev a , N. I. Putincev d, e , and N. Lhamsuren f a Zhitkov Russian Research Institute of Game Management and Fur Farming, ul. Preobrazhenskaya 79, Kirov, 610000 Russia e-mail: saveljev.vniioz@mail.ru b National University of Mongolia, Ulan-Bator, 14200 Mongolia e-mail: shar@num.edu.mn c Hovd State University, Hovd, Mongolia e-mail: otgonbaatar_2004@yahooo.com d Tuva State University, Kyzyl, 667000 Russia e-mail: ecotsu11@yandex.ru e Ubsunurskaya Kotlovina State Nature Biosphere Reserve, ul. Kalinina 19, Kyzyl, 667010 Russia f Administration of Strictly Protected Areas of Uvs-Nuur Basin, Ulangom, Mongolia e-mail: lhamaa_uvs@yahoo.com Received December 5, 2013 Abstract—The modern status and population trends of three alien semiaquatic mammals in a transboundary (Mongolia/Russia) ecosystem of the Uvs Nuur Hollow were studied. The muskrat, American mink, and Eur- asian beaver (Sino-Mongolian subspecies) have almost equivalent size of “life arenas,” but different popula- tion trends, different success in naturalization, and different impact on native ecosystems. It is concluded that differences of naturalization in these three mammals are defined not by postintroduction history or the effect of some abiotic factors, but by the diversity and abundance of trophic niches in the Uvs Nuur Basin. It is stated that, in the conditions of a sharply continental climate and a rigid hydroregime, the adaptation to a new ecosystem is easier for herbivorous mammals having richer and stabler food resources than for carnivorous animals. The behavioral adaptive mechanisms promoting naturalization are described. The evolutionary sta- bility of the building instinct is very important for beaver colonization of new habitats. The utilitarian value of alien species for the human population of the given territory is estimated. Keywords: American mink (Neovison vison), muskrat (Ondatra zibethicus), Eurasian beaver (Sino-Mongolian subspecies Castor fiber birulai), introduction, naturalization, distribution, Uvs Nuur Hollow DOI: 10.1134/S2075111715010051