The modern period is characterized by the expansion of the areas of a number of dangerous infectious diseases, previously endemic only for the countries with tropical climate. As a result of Palearctic climate warming and humidification and under the influence of anthropogenic factors, foci of a new transmissible arboviral zoonosis – West Nile fever (WNF) – have been formed in the Saratov region. On the territory of Russia, the circulation of the West Nile virus (WNV) has been recorded since 1963, and cases of human infection have been detected since 1967. In the studied region, the circulation of the virus has been known since the mid-90s of the last century, and epidemic complications – since 2012. 142 cases of the disease were reported in 2012–2020. The ecological prerequisites for a wide circulation of WNV are associated with the increase in the number of birds – carriers, and arthropods – blood-sucking vectors, the longer activity period of mosquitoes and ticks owing to the reduced frosty season of the year. As a result of landscape mapping with the use of modern methods for decoding images of satellite maps and remote sensing of the Earth (ERS), data have been obtained that served as the basis for epidemiological WNF zoning. There are three types of potential WNF foci on the territory of the region, namely: natural, natural-anthropourgic, and anthropourgic ones. The total area of biocenoses has been established, where natural, natural-anthropourgic and anthropourgic WNF foci could be formed: 6619.94 km2, 1484.62 km2, and 70.4 km2, respectively. Cluster analysis of the environmental conditions in 38 administrative districts of the region has distinguished four groups differing in the risk level of infection of the population with West Nile fever. The data obtained are used for planning, substantiating and conducting surveys and preventive measures, and form the basis for predicting the epidemiological situation in the region.

The morphological characteristics of the North American invasive species Kellicottia bostoniensis Rousselet, 1908 were studied in 29 various types of water bodies and watercourses of the Middle Volga basin. The water bodies, which are the habitats of K. bostoniensis, are located on several territories that differ significantly in a set of characteristics, such as their geological structure, relief, climate, anthropogenic impact, hydrochemical and hydrophysical indicators, etc. The sizes of K. bostoniensis individuals in most of the studied water bodies and watercourses were measured and analyzed for the first time. A high positive correlation was found between the total body length and the posterior spine length (R2 = 0.79, p < 0.01), as well as the anterior spine length (R2 = 0.75, p < 0.01). A relationship was revealed between the lengths of the anterior and posterior spines (R2 = 0.58, p < 0.01). K. bostoniensis individuals in the studied water bodies and watercourses are characterized by large sizes, the median values of the total body length being 236–440 μm. These sizes are similar to those of individuals in the native habitats of North America and some biotopes of Europe and European Russia. Among the previously studied water bodies of Russia and other countries (Belarus, Sweden, Finland, Brazil, and Argentina), where researches of the morphological variability of K. bostoniensis were carried out, the largest body sizes were characteristic for the invader species of the Sura River. Larger K. bostoniensis specimens live in deep mesotrophic water bodies with high transparency, compared with representatives of this species in shallow eutrophic water bodies with less transparency in the Middle Volga basin. Our data on the morphological characteristics of the invading species of water bodies in the Middle Volga basin significantly expand the existing information on the morphological variability of K. bostoniensis individuals and their dependence on environmental factors.

The paper presents the results of the spatial distribution analysis of 18 Globularia bisnagarica L. coenopopulations in the Saratov, Samara, Ulyanovsk and Orenburg regions and the Republic of Tatarstan. The analysis was carried out with the Spatstat package of the R environment for statistical computing. The research reveals an aggregation tendency for the G. bisnagarica coenopopulations. It is suggested that this tendency may be attributed to the prevalence of seed reproduction and certain peculiarities of dissemination (barochory) in the studied coenopopulations as well as to the confinement of the species to eroded landforms (slopes of watersheds, gullies, runoff hollows, etc.) characterized by high heterogeneity of environmental conditions. It has been established that the majority of G. bisnagarica coenopopulations grow in heavily or moderately sodded habitats. Nevertheless, in the studied communities, G. bisnagarica occurs abundantly and dominates along with Stipa pennata, Bromus inermis, Salvia nutans, Elytrigia repens, Poa compressa, etc. Finally, the spatial structure of G. bisnagarica coenopopulations is impacted by the interspecific competition in calciphilous phytocenoses under the invasion of eurybiontic steppe grasses.

For the first time, a comparative analysis of the specific diversity, changes in the biomass of macrophytobenthos in the reserve “Karan’sky” coastal zone from 1964 to 2016 was performed on the basis of a landscape approach. A landscape map of the underwater coastal slope has been drawn up, three bottom natural complexes (BNC) have been identified. The BNC of psephite deposits dominated by C. crinita and Tr. barbata (up to 89.7–78.6% of the total biomass of macrophytes) is the main one. This complex is characterized by high floristic diversity and maximum values of the biomass of macrophytobenthos. The BNC of psephite deposits with C. crinita and Tr. barbata to predominate and with pebble-gravel deposits with broken shells alternate, where Ph. crispa is the dominant species, is characterized by high floristic diversity and a decreased proportion of C. crinite and Tr. barbata, the contribution of Ph. crispa to the total biomass of macrophytes is 14.4%. The BNC of psammitic deposits with Ph. crispa to predominate and with separately randomly located blocks, where Nereia filiformis and Zanardinia typus predominate, is characterized by low floristic diversity, the predominance of Phyllophora crispa (74.3% of the total biomass of macrophytes), and the preservation of perennial species. For more than 50 years, there was a reorganization and degradation of the plant component in all BNC (depth 0.5–10 m), which was probably due to the intensification of anthropogenic activity in the coastal zone. Eudesme virescens, Dictyota dichotoma, Feldmania irrgularis, Dasya baillouviana and Rhodochorton purpureum, which live in clean, open areas of the coast, have disappeared from the bottom vegetation, and macrophytes (Cladophora laetevirens, Ectocarpus siliculosus and C. virgatum), typical for eutrophic waters, have appeared in the duodenum. The biomass of epiphytes has increased (from 0.1 to 42.6% of the total biomass of macrophytes), and the role of dominant species has decreased: C. crinita, Tr. barbata (from 99.9 to 78.6%) and Ph. crispa (from 52.9 to 14.4% of the total biomass of macrophytes). The organization of the “Karan’sky” Reserve contributed to the preservation and partial restoration of the unique natural complex of marine flora and bottom vegetation, which is confirmed by the increased floristic diversity of algaeindicators of clean waters and the increased proportion of the Red Data Book species.

Data on the weather conditions and monitoring of vegetation ecosystems in the Northern Caspian semi-desert for the 70-year period were analyzed. A gradual increase in the average air temperature per hydrological year by 2.73ºC (0.039ºC/year) has been revealed. Before and after the 2000s its increase was caused by warming of the cold and warm period of the year, respectively. An increase of the annual atmospheric precipitation in the spring-summer period was detected, mainly in 1978–1995 due to April-June precipitation. The humidification coefficient dynamics allows distinguishing three periods. The first period (1951–1977) is characterized by insignificant fluctuations around the average value (0.30); the second period (1978–1994) is characterized by good moisture, and the third period (1995–2020), on the contrary, – by severe aridity. These climate changes have led to significant transformation of the snow cover formation mechanisms, the surface runoff of spring melt water, and the ground water level. Despite such fluctuations of natural conditions, the annual productivity of virgin vegetation remains in dynamic equilibrium, changing over time in a wave-like manner, with no introduction of heterogeneous species. The protective afforestation has no chance for sustainable development due to warming of the winter months by 2000, which led to the absence of additional moistening of forest crops for a long period due to the deficiency of snow accumulation and surface inflow of spring melt water. The shrinkage of forest stands was intensified by recurrent annual summer atmospheric droughts. The production of agricultural crops was discontinued since the mid-1990s due to their annual failure, as well as the aridity of the growing seasons. The climate warming of the last two decades has brought the landscape of the flat semi-desert territory of the Northern Caspian region ever closer to its original state without agricultural fields and forest plantations. The population of the region is forced to return to extensive cattle breeding, which has existed here since ancient times.

Habitat niche breadth for Palearctic Arvicolinae species was estimated at both local (α- niche) and global (the entire geographic range, γ-niche) scales using occurrence records of species and environmental (climate, topography, and vegetation) data. Niche breadth was estimated in the space of the first two principal components of environmental variables using kernel smoothing of the densities of species occurrence points. The breadth of α-niches was estimated for a set of random points inside the geographic range in a series of buffers of increasing size around these points. Within each buffer, we calculated the overlap between the distribution of environment values for the kernel smoothed densities of species occurrence points and the distribution of environment values in the background environment. The α-niche breadth was calculated as the slope of the linear regression of the niche breadth for buffers of different size by the ln area of these buffers with a zero intercept. The γ-niche breadth was calculated as the overlap between the distributions of environmental values for the kernel smoothed densities of species occurrence points over the whole geographic range and the distribution of environmental values in the background environment and also approximated by linear regression of the species’ average α-niche to the geographic range area of this species. The results demonstrated that the geographic range size was significantly related with the α- and γ-niche breadth. The γ-niche breadth was significantly positively correlated with the α-niche breadth. Finally, the differences between the γ-niche breadth values that were directly estimated and extrapolated from the α-niche breadth (Δ) values were positively correlated with the geographic range size. Thus, we conclude that the species occupy larger geographic ranges because they have broader niches. Our estimations of the γ-niche breadth increase with the geographic range size not due to a parallel increase of the environmental diversity (spatial autocorrelation in the environment).

In the course of our long-term studies of the phenology of spawning migrations of anuran amphibians, which began in the Medveditsa river valley (near the Uritskoye village, Lysogorsky district, Saratov region) in 2009, an abnormally early end of the wintering period was recorded for the red-bellied toad (Bombina bombina) in the spring of 2020, namely, March 13. The anomaly was longer than a month in relation to the long-term average date of arrival of this species to its spawning grounds (April 18). The water temperature in the shallow waters of the spawning reservoir on this day was 10.2°С to a depth of 0.1 m, and 4.8°С at a depth of 0.5 m, and did not differ significantly from the average values typical for this phase of the B. bombina annual cycle in adjacent populations. The possible significance of this anomaly for the reproduction of local populations of B. bombina is discussed.

The paper considers the fact of the black woodpecker (Dryocopus martius L.) colonization of the Dyakovsky (Saltovsky) forest area, which occupies more than 18,000 hectares on the Yeruslan sands in the Saratov and Volgograd Trans-Volga regions. This forest area is located 25 km from the semi-desert of the Caspian lowland. According to our data, the black woodpecker appeared in the Dyakovsky forest in the winter of 2011–2012 after an extensive fire in the very hot summer of 2010. The mass of dead trees led to an outbreak of xylophagous development, which most likely led to the emergence of a settled population of the black woodpecker in the Dyakovsky forest. For 10 years, we have been conducting observations of the named population. Using the route method, parameters of its density in the winter period were determined, part of the nesting sites was identified, which confirms the year-round habitation and reproduction of the black woodpecker in the Dyakovsky forest. Our observations of the black woodpecker dispersal in the Trans-Volga region are consistent with the data of those authors who established the appearance of this species on the Lower Volga in the Volga-Akhtuba floodplain. In all likelihood, the black woodpecker dispersal in the Trans-Volga region is associated with both some change in the structure of habitats, with some increase in the abundance of this species in the main part of the habitat, and with other factors cited in this work. According to modern concepts, the location of habitats is determined by the “climatic space”, which is potentially suitable for the settlement of a particular species. Other factors interacting with the climate determine the actual development of the territory of this space by the species. Such facts of changes in the boundaries of the habitats of separate species as a result of climate change and factors interacting therewith are widespread in the world.