The fertility and viability of pollen grains of two morphological forms of Taraxacum officinale Wigg. s.l were estimated. These forms compose common coenopopulations growing in various coenotic and edaphic conditions. The studied forms have a developed gynoecia – a large number of fertile pollen grains capable of germination under certain temperature conditions. This points to the amphimictic properties of the plants. Comparison of data on the fraction of fertile pollen grains and seed productivity allows one to assume that some seeds develop without going through fertilization. This can be treated as evidence of the apomictic properties of the plants. Therefore, the presence of optional apomixis in the species in question was indirectly confirmed in the course of our work. The fertility of pollen grains was shown to be a more ecology-dependent property of the male gametophyte than its viability. In the favorable conditions the part of fertile pollen grains in f. dahlstedtii and f. pectinatiforme differs insignificantly. Under stress conditions, the differences between the forms of the dandelion by this indicator amplify. This can be considered as a mechanism of adaptation to adverse environmental factors. The revealed differentiation of the morphological forms of the dandelion by the indicator of the fertility of pollen grains enables one to assume that edaphic and coenotic stresses lead to an increase in the differences between them by the degree of apomictic and amphimictic properties. The morphological forms of the dandelion, realizing two reproductive strategies under stress conditions, support both the quantity and genetic heterogeneity of the coenopopulations. The morphological forms studied do not differ in the proportion of viable pollen grains. This indicator rises to a certain extent only in the gradient of coenotic competition. This can be considered as a manifestation of the properties of optional apomict.

The demographic structure of 39 coenopopulations of Tulipa suaveolens Roth in the Lower Volga region was studied. It has been shown that they occupy an area from 0.01 to 20,000 ha and more. Small-area populations grow mainly closer to the northern border of the species’ range. The density of all individuals (1.6–240.7 PCs/m²) and the number of generative plants (0.1–58.2 PCs/m²) at the interpopulation level varied over a wide range, but changed significantly over years mainly in the populations exposed to recreational load or grazing. The fraction of generative individuals ranged from 2 to96%. In 2013–2016 there was a significant negative correlation between the geographical latitude corresponding to the place of growth of a coenopopulation, and the proportion of plants of generative state therein. On the contrary, in 2017–2018 in the South and West of the surveyed part of the habitat the plants of the pregenerative period prevailed while the share of flowering plants significantly decreased. The observed dynamics correlates well with the weather conditions of the growing season of tulips. In 2013–2016, in the southern part of the territory studied, arid conditions were formed just in the spring and seedlings fell out at an early stage of their development. The spring periods of 2017 and 2018 were wetter there, and seedlings successfully passed through the early stages of ontogenesis. That is, cyclical fluctuations of weather conditions significantly affect the demographic structure of T. suaveolens coenopopulations. Accordingly, the contribution of different years to the renewal of populations is different. The populations in the southern regions maintain a high number of individuals and occupy larger areas mainly due to their long life. Rare seasons with favorable weather conditions provide outbreaks of juvenile plants. In the northern regions of the studied territory, more favorable conditions for the development of sprouts of this species are formed, and fluctuations in the demographic structure of coenopopulations are less pronounced.

The number of pores in the seismosensory canals of some paired cover head bones was counted in specimens of the roach and European perch caught in 15 small ponds in the Central-Eastern part of the Udmurt Republic. On the basis of the data obtained, three indices of fluctuating asymmetry were calculated and a statistical analysis was carried out of relationships between these indices and the average (over several years) values of water mineralization of these waterbodies in different periods of the growing season and with the coefficients of their variation. In the roach the average fraction of asymmetric variants of the studied traits was significantly related with the seasonal variability of water mineralization values only, while the perch showed close and statistically significant relationships of this index with the average values of water mineralization in some periods of the growing season. Another index of the roach was similarly associated with these values, namely, the variance of the fluctuating asymmetry of the total values of the paired counting features of the head seismosensory system. Possible mechanisms of the mineralization factor influence on the degree of asymmetric manifestation of the studied traits are discussed considering peculiarities of their gradual formation in the early ontogenesis of the two fish species. As a result, some limitations of the adequate use of these indices in bioindication of anthropogenic pollution of fresh water with dissolved inorganic substances are considered.

The paper summarizes the data obtained over 50 years of research on habitat selection, nest site choice, breeding behaviour and characteristics of nests in the Willow Warbler Phylloscopus trochilus acredula (Linnaeus, 1758) in the taiga zone of North-west Russia. In this region, Willow Warblers prefer various coniferous-deciduous forests, marshy spruce forests and spruce-pine forests while selecting their nest biotope. During nest site selection, these birds pay attention to the structure of plantings, presence of glades, clearings and other open spaces. Willow Warblers need to have free space with no barriers in front of the nest to get better visibility, reliable masking of the nest by the closest surroundings and the presence of support for the nest. Females build their nests during 4–11 days, on average 7.0±0.5 days. The construction of nests and the nest material composition are characteristic of the species as a whole. At the same time, such features of some nests as the presence of some specific material or the insufficient strength of some elements are due to peculiarities of the occupied habitats.

The density dynamics of nesting pairs of five lark species (Alaudidae) living in the territories of the Mezhuzensky and Uzeno-Dyurinsky plains, on the northwestern tip of the Caspian lowland, and in the semi-desert of the Aleksandrovo-Gaysky district of the Saratov region, and its relationship with Selyaninov’s hydrothermal coefficient are considered. Our research was carried out on 40 fixed routes of 1 km each in the nesting period of the annual lark cycle from 2011 till 2019 (annually). It was established that the abundance dynamics trends were negative in four lark species, namely: the calandra lark  (Melanocorypha  calandra),  white-winged  lark  (M.  leucoptera),  black  lark (M. yeltoniensis), and lesser short-toed lark (Calandrella rufescens); and were positive in the skylark (Alauda arvensis). The calculated trend of hydrothermal coefficient indicators for the described territory demonstrates a 5.4% annual increase in the moistening of the semi-desert zone of our survey area. To assess the relationship of the density of different lark species with the values of Selyaninov’s hydrothermal coefficient, we calculated the Spearman correlation coefficients. When analyzing the data obtained, it was found that a high positive density-moisture correlation was observed for the skylark, calandra lark, and black lark. No such relationship was found in the white-winged lark, and a high negative correlation of the density of nesting pairs with the hydrothermal coefficient was found in the lesser short-toed lark. Based on our research, it can be assumed that moistening of the semi-desert territory is one of the main factors that determine the abundance dynamics of larks. The heat-moisture ratio determines the level of vegetation and, accordingly, the quality of the lark habitats.

The paper presents data on the effect of gall mites on the state of the photosynthetic apparatus of the leaves of woody plants. The material was collected in the territory of the Dendropark of foresters of the Kirov region, located within the city of Kirov (a sub-zone of the southern taiga). To estimate the plant damage degree by gall mites, 100 leaves were collected from each site (10 leaves from each of 10 trees). At the sites with the greatest degree of damage by galling agents, 50 damaged and 50 unaffected leaves were randomly selected, whose length and width were measured. Leaves for the analysis of photosynthetic pigments were selected in the first half of the day (10:00–12:00). Leaf samples (0.15–0.25 g) were fixed with 100% boiling acetone. Plastid pigment content in the extraction was assessed using a SPEKOL 1300 spectrophotometer (Analytik Jena, Germany). Chlorophyll a, b, and carotenoids were analyzed at the wavelengths of 662, 644, and 470 nm, respectively. In the studied area, six species of gall mites widely distributed within the tree range were found on the leaves. Leaves on the linden were damaged by Eriophyes leiosoma and E. tiliae, on the bird cherry tree were by E. padi, on the aspen tree – by Aceria varia, on the rowan tree – by E. sorbi, and on the elm tree – by E. ulmicola. All the identified gall-forming species were monophagous. The most numerous species were the bird-cherry tick (E. padi) and the carob lime tick (E. tiliae). Leaf damage by gall mites did not significantly affect the size of the leaves, but led to changes in the pigment complex. The colonization of leaves with phytophages caused a decrease in the content of plastid pigments therein. Among the plants studied, the linden and bird cherry were more susceptible to damage by the galls; to a lesser extent, there were changes in the pigment fund under the action of the ticks of elm, ash and aspen. The revealed changes in the photosynthetic apparatus of woody plants when damaged by gall mites indicate the danger of this group of phyllophages for tree plantings in urbanized areas.

The paper presents the results of comparative analysis of the terms and duration of phenological phases in the little gopher population in the central part of the Ergenin Upland in 1926–1932, 1972–1982, and 2000–2015. It was observed that in 1926–1932 all the main phenological stages of vital activities in the little gopher populations took place exclusively during the spring-summer period (March–August). It was substantiated that under the influence of the current climate warming conditions in 2000–2015, as compared to 1926–1932, the emergence from hibernation had started to occur in winter months (January–February). The start and end of the gestation period was registered between the first ten days of February and the third ten days of March. Respectively, the preparation to hibernation (battening) among the adult specimens happened earlier (March–April) and terminated, predominantly, in May. The first appearance of the young stock on the surface and its dissemination started to take place in April–May. Young animals’ going dormant in mass was noted in late June-early July. An upward trend, as compared to the period of 1926–1932, in the total duration of young stock hibernation (July–January or February) was noted. The lower intensity of feeding migrations among adult gopher individuals to topographically low areas was also revealed.

An attempt has been made to assess the status and trends of ecosystems of differenttype reservoirs in Europe and Asia (the Saratov and Volgograd ones, closing the Volga cascade, and the Iriklinsky one, which is the largest on the Ural river) on the basis of the relationship of basic hydrochemical parameters. The ecological status of water bodies was considered from the position of the stability of their ecosystems, which was evaluated using some statistical approaches based on the data of long-term monitoring. The proportion of variability of the main components, the index of plasticity (reliability) corresponding to the average module of the correlation coefficients of hydrochemical parameters were calculated. The desirability function method for qualitative assessment of aquatic ecosystems, characterized by a large number of hydrochemical parameters, was applied. This method allowed minimizing a large amount of information and overcoming the dimension problem. The results of the application of the calculated statistical indices allow us to consider the volume of water flow and summer water temperature as the main factors affecting the content of basic hydrochemical ingredients in the Volgograd and Iriklin reservoirs. The hydrochemical regime of the Saratov reservoir, due to its high flow rate, is determined mainly by the waters coming from the Kuibyshev storage reservoir, and therefore such dependencies were not established. During the study period, the entropy index in the Volga reservoirs fluctuated at the same level, but significantly increased in the Iriklinsky one. The highest values of plasticity are characteristic for the Iriklinsky reservoir, which has the greatest spatial and seasonal heterogeneity of its aquatic environment. During the study period, there have been trends of increasing plasticity in the Saratov reservoir and decreasing in the Iriklinsky one. A decrease in the desirability function indicates some destabilization of their ecosystems.

Modern methodological approaches were applied to analyze the zooplankton community spatial distribution (with the example of the middle river part of the Cheboksary Reservoir). Zooplankton communities were sampled in the middle river part of the Cheboksary Reservoir (from the city of Nizhny Novgorod to Vasilsursk town) in the summer low-water period in 2018. The boundaries between the communities in the Cheboksary Reservoir were gradually changing during the history of the Cheboksary Reservoir from the time of its construction to present. In the middle river part of the Cheboksary Reservoir there are two distinct spatially stable zooplankton communities associated to the Oka and Volga streams. The distinction between these two zooplankton communities was demonstrated by hierarchical cluster analysis. Redundancy analysis has shown that chlorophyll-a and pH were the main factors influencing the specific zooplankton structure. Chlorophyll-a concentration reflects the meso-scale heterogeneity of the horizontal phytoplankton distribution and hence the distribution of the zooplankton’s food sources. The relation of zooplankton to pH level reflects the high sensitivity of the species of the genus Brachionus Pallas, 1766 to high acidity. The influence of pH as an environmental factor was less evident. However, this variable is well known as one of the leading factors determining the structure of zooplankton communities. Its role in zooplankton community assembly of lowland reservoirs deserves further investigation.

The feeding of Lacerta agilis was studied by means of the content analysis of lizards' stomachs conducted in the vicinity of Saratov City from April till September 1983, 2003 and 2007. The maximum daily diet was characteristic in July and reached 2.5–2.7 g/day, while the minimum one was in April and September (1.1–1.2 g/day). The highest and lowest numbers of food objects were recorded in May and September, respectively. Insects are the basic food objects of L. agilis, their occurrence frequency being 100% during the whole active-life period. Coleoptera representatives predominated in  the  diet  (25.4–40.5% by  number, 43.5–70.9% by  weight). The  fractions of Lepidoptera, Hymenoptera, Diptera, etc. were somewhat lower. Well-flying and quickly-moving insects predominated in the food spectrum of L. agilis. Rather many invertebrates with cryptic colour, poisonous, stinging and badly smelt ones were frequently met among the nutrition objects. Moreover, vegetable remains (seeds, leaves, flower fragments etc.) and various small stones to act probably as gastrolytes were found in many stomachs.