Living on the edge: distribution patterns of steppe mammals in Transcar­pathia (Ukraine)

We analysed the composition of the steppe assemblage in the mammal fauna of Transcarpathia (Ukraine), which is represented by three rodent species such as the European ground squirrel Spermophilus citellus, the common hamster Cricetus cricetus, and the steppe mouse Mus spicilegus. These species have not been considered in the composition of the local fauna or they were mentioned only in general checklists, or even with obvious mistakes in descriptions of both key characters and record localities. Here we present detailed descriptions of distribution of each steppe species based on actual record localities as well as ecological and biogeographic features. In total, we have generalized data on 13 record localities of Spermophilus citellus, 7 of Cricetus cricetus, and 8 of Mus spicilegus. We also revealed and described general trends in the distribution of these species: all of them occur in the lowland part of Transcarpathia between the valleys of the Tisza and Latorica rivers and adjacent areas. Generally, steppe species in Transcarpathia are related to anthropogenically transformed biotopes: the European ground squirrel mainly occurs along banks of dammed rivers in zones of floods, while the common hamster and the steppe mouse are both related to agricultural lands. The absence of natural populations in indigenous biotopes and, in fact, the absence of typical key steppe habitats suggest that steppe species appeared in Trans­carpathia as the result of expansion from their main geographic range as suitable habitats gradually appeared at the range periphery. The closest centre of distribution of each species is located beyond the studied region, namely in the Great Hungarian Plain, and the records described here are marginal: they are instable and attributed to the zones of range pulsation, which depends on climatic factors and current landscape features of the lowland part of Transcarpathia. The state and dynamics of range-edge populations of steppe species in Transcarpathia might be largely affected by the hydrological regi­me, wintering conditions, human activity, etc., as well as by “edge effects” that usually take place in fragmented populations. The influence of such processes probably could explain the low abundance and rarity of steppe species in the region, and, in the same time, makes topical the issue of their conservation. At present, conservation issues especially concern two species, namely the European ground squirrel and the common hamster, which are keystone species in steppe and forest steppe ecosystems.