Distribution, habitats and abundance of the Eurasian Least Shrew Sorex minutissimus (Eulipotyphla, Soricidae) in the North-East of the European part of Russia

Eurasian least Shrew, Sorex minutissimus, occupies large area in Northern Eurasia from Norway, Sweden, and Belarus to the Pacific Ocean shore, and Sakhalin and Hokkaido islands. It is marked in Mongolia and China, in Northern America (Alaska) and in western part of Canada. Sorex minutissimus can be met in different zones from forest tundra in the North through boreal spruce forests to mixed forests and forest steppe in the South. The Eurasian least Shrew is rare species all over this area. In addition, it is very difficult to catch shrews with usual catching methods. Thus, the distribution and ecology of this species have not been studied enough until now. The northern boundary of this area, within North-East of European part of Russia, is almost unknown. Until recently, only five records of Sorex minutissimus were registered on the region territory. This work aims to analyze all materials of the last decades on Eurasian least Shrew distribution in the North-East of European Russia and summarize the data on biotopic distribution of this species and its number. To catch and count shrews, we used standard 50m length trench with five catching cones embedded in the bottom. We considered the number of caught animals per 100 cone-days as count index (an. per 100 c-d.). Mean indexes of species abundance were indicated based on long term counts in eight locations. Three of them (Yany-Pupunyor, Garevka, and Kybla-Kyrta) are located in the Ural Mountains, one in extremely northern taiga subzone (Karpushevka), one in plain northern taiga subzone (Kamenny), and the last two in medium taiga subzone (Dan’ and Yaksha). Over the last 30 years, we could discover 14 new habitats of Eurasian least Shrew. It undoubtedly inhabits wider area, but catching trenches, which can catch this species, were used in very little number of habitats. For example, this only can explain the absence of the Eurasian least Shrew species in the Subpolar Urals. All records of Eurasian least Shrew are located in taiga zone of the region. This species was not found in European plain tundra and forest-tundra. The northern boundary of this area from Pinega State Reserve to the East crosses of the Mezen’ River in its lower course. On the territory of the Republic of Komi, the most northern habitats where the species was found are the middle stream of the Tobysh River (66º00′15′′N, 51º08′29′′E) and the outskirts of Karpushevka village (See Fig. 1, See Table 1) in extremely northern (thin) taiga subzone. From here, the northern distribution boundary of the Eurasian least Shrew in the region goes to the central Polar Urals, where it was caught on the eastern slopes of Rai-Iz Mountain. In the Northern Urals on the territory of Pechora-Ilych State Reserve, it was found both in the South (Yany-Pupunyor Mountain Ridge) and in the North (Saran-Iz Mountain Ridge) of the mountain area. The Eurasian least Shrew is considered as the one of most eurytopic species of shrews. In taiga zone of the North-East of European part of Russia it inhabits different biotopes: spruce and pine forests, cleared spaces, meadows, upland bogs, and ecotones (boundaries of biotopes). The use of index of fidelity to biotope made it possible to find preference of Eurasian least Shrew to communities of taiga type (See Fig. 2). This connection occurred in all studied habitats. Shrubby green-moss spruce forests are the optimal stations. In these biotopes, were caught 90.9% of all animals in Kamenny locality and 85% in Yaksha, respectively. In Dan’ habitat, more than 50% of all shrews were caught in two biotopes – sphagnum-moss spruce forest and shrubby green-moss spruce forest. Similar biotopic preferences were registered in other areas on European North as well [12]. In some localities, cleared places of different type and green-moss pine forests were also among the preferred biotopes. A specific feature of Eurasian least Shrew is omnipresent low abundance. This is also typical for territory of the North-East of European part of Russia, where mean abundance indexes in different locations vary from 0.2 to 1.2 an. per 100 c-d. (See Table 2). The Sorex minutissimus occupies one of the last positions in the population of shrews with its share ranging from 0.1 to 1.8% in different regions. Some possible causes of habitat versatility and low abundance of least shrew may be due to energetic features of this species. Very small body size requires significant energy loss for survival of this species. Therefore S. minutissimis is exigent to local environmental factors (humidity, micro-climate, and food resources). Micro-stations, which occupy small territory in different habitats, are the optimal environment. Small (< 4-5 mm), abundant and accessible arthropods with high occurrence are prevalent in feeding of least shrew; thus, this species (if relevant environmental factors are present) occupies many biotopes, including poor habitats. However, the abundance of least shrew is restricted by fragmentarity of its population and low ecological capacity of micro-stations.

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