Formation of the abundance of rodents in pyrogenic habitats
The research of the stability of natural ecosystems to the influence of external negative factors is an important and urgent problem, as in recent decades there has been an increase in the frequency and scale of natural forest fires, both on the territory of Russia and in the world as a whole. The aim of the research was to study the formation of the abundance of rodents in pyrogenic habitats after two differently occurring natural fires using the example of their three co-inhabiting species. We investigated fire-damaged biocenoses of the Visimsky Reserve (57°20'-57°31'N, 59°30'-59°50'E, Middle Urals, Russian Federation). We conducted our study in two adjacent sites affected by fire to varying degrees: site 1 burned twice - in 1998 and 2010, site 2 was subjected to a single exposure to a fire in 2010. The objects of study were cohabiting (sympatric) rodent species of the genus Clethrionomys (Myodes) - bank vole (Cl. glareolus Schreber, 1780) and grey-sided vole (Cl. rufocanus Sundevall, 1846), as well as a representative of the genus Sylvaemus, small forest mouse (S. uralensis Pallas, 1811). The animals were caught by a standard trap-line method. The total number of traps placed at 10 m from each other in two sites was 200 (100 traps each). The relative abundance of individuals was assessed by their number in the first five days of catching in converting of 100 trap-days (samples/100 trap-days). A comparative analysis of the relative abundance of the three species of rodents at two disturbed sites was carried out in the two previous catastrophes (19961997, 2008-2009), during the years of fires (1998 and 2010), and annually during the five-year period after the impact of each of the fires (1999-2013 and 2011-2015, respectively). Traps throughout the study period were located in the center of the same test squares of 10 m<sup>2</sup>, in which quantitative descriptions of the characteristics of the protective and feeding microhabitat conditions of animals in 9 variables were carried out. The area of the cover was assessed by moss, grassy vegetation, shrub, lying tree trunks, tree branches, stumps and dry trunks. We also considered the total number of underwood, living trees and measured the width of the path within the plots. This study uses the results of quantitative descriptions conducted in 1999 and 2011, i.e. a year after the occurrence of each of the two fires. We showed that the formation of the number of three sympatric species of rodents at the sites disturbed by fires occurs at different rates. The revealed differences are explained on the one hand by intrapopulation characteristics (types of functioning of local groupings), and on the other hand by the abundance level of species and their biotopical preferences at the initial stages of post-pyrogenic successions of forest biocenoses. The analysis allows us to conclude that pyrogenically transformed forest communities are ecologically unfavorable for the grey-sided vole, but microhabitat conditions are most preferable for the bank vole and small forest mouse at the twice-disturbed site, as evidenced by higher rates of recovery of the numbers of these species, in contrast to biotopes damaged by one fire. The article contains 3 Figures, 3 Tables, 32 References.