TO THE ECOLOGY OF THE SIBERIAN (<i>LEMMUS SIBIRICUS)</i> AND THE DISTRIBUTION HISTORY OF THE COLLARED (<i>DICROSTONYX TORQUATUS</i>) LEMMING (RODENTIA, CRICETIDAE) ON THE NEW SIBERIAN ISLANDS
120 Siberian lemmings (<i>Lemmus sibiricus</i>) were studied from Kotelnyi Island in the eastern sector of the Polar basin. The main habitats, abundance, nutrition, shelters, breeding and sex-age structure were described for the first time in the conditions of an arctic climate and a depleted vegetation of the New Siberian Islands. Morphological parameters confirming the subspecific status of the Siberian lemming on these islands are given. The issues that the Collared lemming (<i>Dicrostonyx torquatus</i>) inhabited the archipelago during the Late Pleistocene and in the modern period are discussed. The important roles the Siberian lemming could have played in the vegetation cover, the formation of upper soil horizons, the surface microrelief, microclimate and ecosystem productivity of the island are shown.