Spatial variability of the Siberian brown lemming Lemmus sibiricus (Kerr, 1792) abundance in Western Siberia: Population approaches in distribution analysis

Analysis of small mammal distribution in Western Siberia is often carried out for a group of species as a whole or for one species in a relatively small area. In both cases, the research results are species essays with a brief description of the spatial heterogeneity of quantitative indicators to the placement of animals on the accepted level of data aggregation. The influence of environmental gradients on the distribution of species or groups is usually assessed by given natural and anthropogenic factors; their composition is not formalized and varies depending on the objectives of a particular study. All of the above makes it difficult to generalize the results of studies of the species distribution in different areas, as well as the comparison of data on the spatial variability of biotopic preferences and its causes for different species in the same territory. The main tasks of our research were to compare biotopic preferences, abundance and number across all species of small mammals and to develop a general classification reflecting similarities and differences in their distribution across Western Siberia as a whole. The study is not ecological, but zoogeographic, so the terms should be uniform, at least in seasonal terms. The main zoogeographic meaning of the work is to identify the general patterns of distribution of the studied species and environmental factors that correlate with the spatial heterogeneity of their abundance. Therefore, the preliminary division of the territory into habitats, as well as key sites and time of observations should be uniform. The collected and analyzed information can be used for environmental purposes, in assessing the territorial variability of prey resources for hunting birds and commercially sold fur-bearing mammals, the number of which depends significantly on the level of abundance of small mammals. The aim of this research was to analyze the distribution of Siberian brown lemming in Western Siberia and to assess the impact of the identified environmental factors on its abundance heterogeneity using population methods and approaches. The methods and approaches implemented to study the animal population were successfully used to analyze the distribution of individual species of small mammals. It allows to secure within the limits of strict separation of habitats according to similarities in the abundance and avoid their subjective dividing into groups. The distribution of the Siberian brown lemming was analyzed by the results of small mammal surveys carried out in the second half of the summer from 1954 to 2016 in the plains and mountains of Western Siberia. The abundance indices for all years were averaged by groups of vegetation maps within the zones, subzones and subzonal belts of the plain and mountain provinces. The spatial-typological organization of the biotope distribution was revealed by means of factor classification, one of the methods of cluster analysis. As a measure of similarity, the Jaccard-Naumov coefficient for quantitative characteristics was chosen. To evaluate the relationship of habitat classification, we used the linear quality approximation of the coupling matrix. The total number of Siberian lemming was obtained by converting the relative abundance indicators into absolute ones taking into account the areas of natural zones, subzones and subzonal belts. The relative error and asymmetric confidence intervals of the generalized population estimate are calculated with a confidence probability of 0.9. Siberian brown lemming within the West Siberian plain is widespread to the North of the typical Northern taiga (See Fig. 1). It was not encountered in the Altai and Kuznetsk-Salair mountain regions, although literary sources note its presence in the mountain tundra of the Northern Urals. In structured classification, five types of habitats are identified according to their degree of favorability for the Siberian brown lemming: optimal, suboptimal, subpessimal, pessimal and extreme (See Fig. 2). Most of its abundance is in the tundra and lowland meadow-willow-moss communities in the Northern moss tundra subzone belt (See Fig. 3A). Slightly less favorable are habitats of Arctic tundras. The next type includes swamps to the North of the Middle taiga and non-forest biotopes from low-shrub subarctic tundras to the Northern taiga light forests. The environmental conditions in pre-tundra open woodlands and the Northern taiga light forests are severe for the Siberian lemming. The last, extreme, type of favorability combines areas of the plain to the South of the Northern taiga light forests and mountain areas, where this lemming does not enter. Using the cluster analysis, the list of environmental factors is revealed: heat availability (the mode of zoning and subzoning on the plain, altitudinal zonation and provinciality in the mountains), zoning and subzoning on the plain separately, macro relief of areas (plain-mountains), type of vegetation, forest cover degree, swampiness, pouring in the flood and human development degree. The greatest connection with the heterogeneity of the abundance of Siberian brown lemming is traced for heat availability and zoning and subzoning (See Table 1). The other factors are less significant, their local influence is undoubted, but small, in general, for the studied area. Multiple evaluation of the relationship with all identified environmental factors and their combinations gives 78% of the recorded variance (multiple correlation coefficient 0.88). In total, the number of Siberian brown lemming in Western Siberia is estimated as 374 million individuals, almost 90% is concentrated in the Northern subarctic tundra of the plain (See Fig. 3B, Table 2). The total number of species depends on the areas of habitats of different favorability by zones, subzones and subzonal belts. Spatial variability of relative abundance (individuals per 100 cylinder-days) and total number (million individuals) is diamond-shaped. These values are declining from the Northern moss subarctic tundras to the North, in Arctic tundras, and to the South from low-shrub subarctic tundras to the Northern taiga light forests.