Close non-murid rodent species in the fauna of Ukraine: differences, biogeography, and ecomorphology

Summaries of taxonomic revisions, analysis of identification criteria, spatial and ecomorphological differentiation of close pairs of species are summed up. Increased taxonomic heterogeneity is characteristic for 4 superspecies: Spermophilus suslicus s. l. (2 species), Sicista subtilis s. l. (2 species), Sicista betulina s. l. (2 species), and Spalax zemni s. l. (2 species). Unlike other groups of small mammals (in particular, bats and rodents of the superfamily Muridae s. lato, seu Muroidei), all these superspecies complexes are represented by allospecies. Accordingly, the differences between them by eco-morphological characters are minimal or absent. It was revealed that sympatry in each group is possible only with species from adjacent taxa of the same ecomorphological groups, in particular, susliks with marmots, forest birch-mice with steppe birch-mice, and mole rats with mole voles. In all these allospecies complexes, all species are related to the forest-steppe or steppe faunal complexes (except for the northern forest birch-mice from the superspecies Sicista betulina s. l.), as well as their spatial differentiation is based on the principal inter-river spaces, and the boundaries of their ranges are large watercourses. One of the key factors of spatial segregation is the delimitation by large rivers, first of all the Dnipro, Dnister, Tyligul, Molochna, and Donets. Cases of sympathy, even marginal, have not been revealed, but the analysis of ancient literature and collections show signs of recent expansion of species. In particular, signs of the expansion of Spermophilus odessanus to the west were detected; probably the same applies to Sicista loriger and Spalax zemni. The key biogeographic coordinate of the whole complex of "small" species of non-Muroidei rodents is the Lower Dnipro, in particular the triangle between the Lower Dnipro, the Black Sea, and the Molochna river. Guilds in all these groups are as simple as possible (practically mono-species), and in addition, three of four of these groups are presented by hibernating animals (fourth group is underground rodents). Unlike other groups of mammalian siblings, all analyzed species do not show any tendency to synanthropy and are in need of special conservation measures