Transformation of Vegetation as a Limiting Factor for the Existence of Rodent Populations in Open Spaces (on the Example of Spermophilus suslicus)

A comparative analysis of the composition and structure of plant communities in two places of former habitation of the speckled ground squirrel (Spermophilus suslicus) in the Nikolaevsky district of Ulyanovsk oblast is given. The analysis of a modern state of the S. suslicus populations in the Volga region demonstrated that over the past fifty years, a critical decrease in the species number (and its complete disappearance in some regions) is observed. A number of researchers note that dynamic changes in the vegetation have a certain effect on these processes. Therefore, the aim of our work was a comparative study of biotope vegetation at the time of a high number of animals against the background of intensive grazing and in the absence of ground squirrel settlements for more than 15–20 years in the absence of grazing. Our studies demonstrated that there is an increase in the species richness and structural diversity of the communities due to the introduction of the species of pine, nemoral, and boreal ecologocenotic groups into their composition. Phytocenoses of steppe meadows with a high involvement of Festuca valesiaca, Poa pratensis, Helictotrichon pubescens, Elytrigia repens after the cessation of grazing are replaced by the cenoses of meadow steppes with a dominance of Bromopsis riparia, Poa angustifolia, Calamagrostis epigeios. There is an increase in the total projective cover of the grass stand (from 40 to 60–70%). Forage species that are background at the moment of high number of animals sharply decrease their involvement in the grass stand. Changes in ecological conditions of the biotopes are typical: modern communities are formed in drier, less nitrogen-rich and “acidic” habitats. A preservation and possible restoration of the speckled ground squirrel settlements in the Volga region is possible under scientifically substantiated anthropogenic effect realized in the form of haymaking and grazing.