The 2020 spring processes in the European Russia were developing according to the type of false spring. The absence or weak development of snow cover, as well as its early descent in the last decade of February, determined the rapid warming of the soil profile. A certain complex of meteorological factors led to an abnormally early start of spawning migrations of the common spadefoot toad (Pelobates fuscus (Laurenti, 1768)) and Pallas's spadefoot toad (Pelobates vespertinus (Pallas, 1771)) over a vast territory which included the northwestern, western, central and southeastern parts of the species habitat in the region. Analysis of the snow cover dynamics and the temperature course according to the data of the network of meteorological stations made it possible to assess the phenology of these species of anuran amphibians within this region using the method of reconstructing the reproductive period events of the spadefoot toads. The duration of the period between the start dates of false and true spawning migrations was more than 40 days in the west, in the center and in the south-east of the European Russia. The abnormally early formation of the 2020 false spring phenomenon in the spawning migrations of spadefoot toads is currently registered as a precedent which may have a significant impact on the reproduction success of the species of this genus.

The influence of the global climate warming on the population dynamics of the small ground squirrel at the border of its range in the northern desert zone on the territory of the Ilmenno-Prideltovy landscape area of the Caspian lowland in 1945–2019 is considered. Data on the numbers of small ground squirrels and the average monthly air temperature in January–February at the Astrakhan weather stations for the last 75 years have been analyzed and statistically processed. It is emphasized that the abundance dynamics of the species is determined by a whole complex of natural and anthropogenic factors. At the same time, in desert conditions, the distribution of air temperature and precipitation by seasons and years is limiting for the small ground squirrel. The January–February temperature effect provoking the awakening of the small ground squirrel from hibernation is analyzed. The high January temperature, followed by the February cooling, led to the mass death of animals, which would subsequently negatively affect the phenology of the main phenomena in the life of this monoestral species, disrupt the population structure and lead to a decrease in the numbers of animals. Against the background of the low January air temperatures, the awakening of the small gopher took place in February–March, and the higher February temperatures provided optimal conditions for a simultaneous exit from hibernation and participation in the reproduction of all sex and age groups of small gophers. Such a combination of January and February air temperatures took place during 1960–1979, which contributed to the growth and preservation of a relatively high level of the species' abundance. The high temperatures of the 1980–2009 winter months provoked the early release of the animals from hibernation: the numbers of ground squirrels decreased and kept at a low level. Against the background of decreases temperatures of the 2010–2019 winter periods, the effect of stabilization of the small ground squirrel population and some increase in the density of the species was observed.

The results of our studies of potential nesting sites for bustards in the Saratov Trans-Volga region are presented. Characteristics of plant communities, as well as the quantitative and qualitative composition of arthropods in these areas, are given. Specific materials obtained in 2017–2021 at 6 plots are given, namely: crops of winter wheat, millet, and sunflower; fallows of various ages; and young (2nd stage) and old virgin lands. The obtained results are compared with the data of previous years. The obtained results on the state of the forage base of bustards allow us to conclude that loss of nesting habitats by birds of this species has actually occurred. Those areas, where, despite the decrease in the abundance of insects, there are still enough of them to feed the chicks, are not used by bustards as nesting stations. These are fallows of various ages and virgin lands. The lack of a sufficient number of arthropods necessary for feeding chicks in those places where bustards prefer to nest, namely, cereals crops, leads to catastrophic consequences for reproduction, and, consequently, the survival of the species. The numbers of large orthoptera and beetles in winter crops, reflecting biomass indicators, have decreased by 10 times compared to 2000, during the period of extensive agriculture. The intensification of agricultural production, the use of pesticides on various crops, as well as the change in the structure of crop rotation are the main causes for the insufficient food supply during the period of rearing chicks. The results obtained give grounds to believe that the number of bustards will continue to decline due to the inability to raise their offspring as a result of the lack of food supply.

The fruits of Trapa natans L. s. l. (Trapaceae), which has disappeared from the territory of the Saratov region, collected in the floodplain lakes of the Khoper river in the Voronezh region (Novokhopersky district), were sown in the fall of 2019 and spring of 2020 into the Khoper and Volga rivers within the Saratov region. In the fall of 2020, 17 recipient populations were observed, and the number of water caltrop rosettes in most of them was less than that of nuts sown. The number of rosettes equal to or greater than that of the nuts sown was observed in three recipient populations only. According to the morphometric parameters of the vegetative sphere, five recipient populations (Nos 6, 7, 9, 15, and 21) from the Khoper river approach the donor ones, while only two recipient populations (Nos 7 and 9) from the Khoper river approach them by the potential and actual seed productivity. The reintroduction of T. natans populations seems more promising in the Khoper river, whilst it is difficult in the Volga river due to sudden changes in the water level during the season.

Data on the leukocyte blood composition of two co-habiting species of freshwater turtles, Emys orbicularis and Mauremys caspica, from the Republic of Dagestan (Russia) are provided. Lymphocytes are the predominant cells in the blood of females and males of both species. Heterophils predominated among granulocytes. Two-way multivariate analysis of variance showed a statistical significance of the influence of two factors on the leukocyte formula of freshwater turtles, namely: species (λWilks = 0.459, p < 0.001), sex (λWilks = 0.809, p = 0.019) and their interaction (λWilks < 0.001, p < 0.001). The blood formula (WBC) of E. orbicularis females showed higher levels of eosinophils (z = 3.040, p = 0.001) and basophils (z = 5.394, p < 0.001) and reduced levels of heterophils (z = 3.579, p < 0.001) and lymphocytes (z = 3.391, p < 0.001) compared to M. caspica females. Males of E. orbicularis differed from those of M. caspica by increased levels of eosinophils (z = 2.716, p = 0.003) and basophils (z = 4.829, p < 0.001) and a reduced level of heterophils (z = 3.474, p < 0.001). With general adaptive responses, interspecific differences were clearly expressed: the variability in the parameters of the white blood cell system of E. orbicularis was associated with rearrangement of the ratio of granulocyte cells (heterophils, eosinophils and basophils). The predominance of a specific component of the immune system (lymphocytes) was found in the immune responses of M. caspica. Changes in the leukocyte profiles of freshwater turtles were associated with a change in the agranulocyte–granulocyte ratio, which was confirmed by statistically significant differences in the integral leukocyte indices. The leukocyte profile of Emys orbicularis testified to the insufficient resource of adaptive mechanisms in specific environmental conditions. On the other hand, the blood formula (WBC) showed the possibility of an active response, more pronounced in M. caspica than in E. orbicularis.

The authors discuss the use of the Greenell concept of ecological niches to analyze the taxonomic structure of communities and their relationship with environmental factors. The modeling of ecological niches was carried out using the results of 30-year studies of macrozoobenthos’ communities on 90 small and 12 medium-sized plain rivers in the region of the Kuibyshev, Saratov and Volgograd reservoirs. Geoclimatic indicators, relief characteristics and hydrochemical assessments of water quality at sampling points were considered as abiotic factors, where 11 variables with the least collinearity were taken. The multidimensional space of the initial abiotic factors was projected onto the orthogonal axes of the first two principal components; there were constructed ordination diagrams with plotted points of presence of species. The model of the potential ecological niche of each species was represented as an area in the space of latent variables, in which the habitat suitability index Z, estimated by the probability density of occurrence, corresponds to the given constraints. The authors used the Schoener and Hellinger indices to quantify the proportion of overlapping niches belonging to two different benthos taxa. The matrix of distances between overlapping niches was formed for all possible paired combinations of 40 most ecologically significant macrozoobenthos species. The cluster analysis of the obtained distance matrix was carried out by the methods of hierarchical agglomeration and fuzzy k-means. In the general multidimensional space of abiotic variables of the studied region, 4 areas of collective niches for groups of species with maximum distances between their centroids were identified. The analysis of intergroup variation of environmental factors is given and the characteristic features of each group are discussed: ecological strategy, biological characteristics and tolerance level.

The results of our studies of resources and the state of coenopopulations of three species from the genus Viola, namely, V. canina L., V. tricolor L., and V. arvensis Murray, conducted in Romanovsky, Balashovsky and Kalininsky districts of the Saratov region in 2016–2021 are presented. Descriptions of the species’ habitats with geographic coordinates are given. The species V. canina, V. tricolor, and V. arvensis have medicinal, honey-providing and decorative value. Populations of the species are confined to meadow-steppe grass-forb phytocenoses. The phytocenoses with the participation of the studied species differ in dominant and codominant species. As a result of our study of the ontogenetic structure of V. canina cenopopulations (CP), it was found that both CPs have unimodal spectra with a maximum on plants of the virginal group. The cenopopulation type according to the «delta-omega» criterion is transitional. The CP of V. tricolor and CP 2 of V. arvensis are characterized by average reproduction efficiency. The CP 1 of V. arvensis has low reproduction efficiency; the value of the recovery index of its age spectrum is less than one. Regeneration processes in CP 1 of V. arvensis are difficult and unstable. Our analysis of the age structure of CPs using the delta-omega classification has shown that the CP of V. tricolor and CP 1 of V. arvensis are maturing, while CP 2 of V. arvensis is transitional by its position in the delta-omega coordinate system. The yield of the species depended on the degree of moisture in the year. On average, over 5 years of the study, the yield of V. arvensis, V. canina and V. tricolor was 21.51, 19.09 and 27.2 t/ha, respectively. In order to restore the populations, the exploitation of thickets of all species of the genus Viola should be carried out once every three years on 1/3 of the area of thickets.