Dynamics of distribution of introduced mammals in Ukraine and factors influencing them

This article considers changes in the composition of the fauna and in the abundance of alien mammals from the group of introduced species over the past two decades, which in Ukraine are marked by two powerful processes. These are the distinct processes of climate warming and shortening of winters, on the one hand, and the large-scale war waged by Russia against Ukraine on the territory of Ukraine, on the other. Such changes in the natural environment lead to significant shifts in the boundaries of natural zones and, accordingly, the living conditions of all species, not only local biota but also aliens. Among the latter, a special group is made up of introduced species, as those that appeared not as a result of natural dispersal in the context of global climate change, but due to various types of introductions. Among them are three species from the superorder Rodentia ( Oryctolagus cuniculus , Ondatra zibethicus , Myocastor coypus ), three species from the superorder Carnivora ( Nyctereutes procyonoides , Neogale vison , Procyon lotor ), five species from the superorder Ungulata ( Cervus nippon , Dama dama , Ovis gmelini , Equus hemionus , Equus ferus ). The following five factors contributed to the success of the introductions: 1) captivity with the possibility to escape, 2) destruction of various kinds of nurseries (during the war), 3) reduction of the abundance of native species, 4) increase in the share of degraded habitats, 5) reduction of all forms of nature use and population regulation. The factors of successful introductions are analysed in terms of habitat types and the structure of guilds in which the introductions are integrated. It is shown that introductions of species confined to eutrophic habitats and species occupying ‘windows’ or marginal places in the guild structure are successful. Most of the introductions carried out in Ukraine have resulted in the formation of natural populations of alien species, mainly semi-aquatic mammals: rodents ( O. zibethicus , partially M. coypus ) and carnivores ( N. vison , N. procyonoides ). Terrestrial species did not show significant expansion and naturalisation, with the exception of the sika deer. The increase in the number of some alien species ( O. zibethicus , C. nippon , N. vison ) occurred simultaneously with a decrease in the number of their competitors from the native fauna ( Arvicola amphibius , Cervus elaphus , Mustela lutreola ). The most problematic was the entry of N. vison into the mustelid guild. The appearance of alien species has led to the extinction of a significant part of ecologically similar native species, and the total number of these two groups of animals has become almost equal. Hunting of animals as a means of regulating their populations has proved to be ineffective, as the volume of hunting is 1–2 orders of magnitude lower than the annual population growth of these species, which indicates that alien species are not vulnerable to hunters.