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In this paper we provide integrative description (morphological and genetic) of the new eutardigrade species Mesobiotus mandalorisp. nov. from central Poland, found during research on the vertical distribution of Tardigrada in the Czerniejewskie Forests. Mesobiotus mandalorisp. nov. belongs to the harmsworthi group, but it differs from the members of this group in some morphometric characters of the bucco-pharyngeal apparatus, claws and/or eggs. Morphologically, Meb. mandalorisp. nov. is most similar to Meb. pseudocoronatus, but it differs from it by a larger bare egg diameter and smaller number of egg processes on egg circumference. Morphometrical data were supported by results of comparative genetic analysis of four molecular markers: 18S rRNA, 28S rRNA, ITS2 and COI. According to COI the new species is most similar to Meb. skorackii with the genetic distance of 21.1%. [ABSTRACT FROM AUTHOR]

The paper presents information about the following eight, either exceedingly rare or infrequently recorded species of short-tongued bees of the genus Andrena Fabricius, 1775 in Poland: A. (Lepidandrena) florivaga Eversmann, 1852; A. (Lepidandrena) rufizona Imhoff, 1834; A. (Melandrena) gallica Schmiedeknecht, 1883; A. (Micrandrena) enslinella Stoeckhert, 1924; A. (Micrandrena) nana (Kirby, 1802); A. (Micrandrena) nanula Nylander, 1848; A. (Micrandrena) pusilla Pérez, 1903; A. (Micrandrena) saxonica Stoeckhert, 1935. This is the third contribution concerning the rare species of the genus Andrena Fabricius, 1775 in Poland. The studies were conducted from 2010 to 2019, and ca. 24,000 specimens from both the museum and private collections of bees of the genus Andrena from Poland were identified. Currently, the Polish fauna has 96 taxa of mining bees of the genus Andrena. For each species, the following information is provided: short diagnosis, remarks on general distribution, bionomics, published records from Poland and confirmed Polish records based on studied collections, as well as current category of threat resulted from the studies. [ABSTRACT FROM AUTHOR]

Despite its broad range and high abundance, nest sites of the European robin Erithacus rubecula, a small forest passerine, are rarely characterised, and most studies refer to human-transformed habitats. In this paper, we describe the species' nest sites in the natural conditions of a primeval forest. We also investigate robin preferences to address nest site selection which can only be assessed if the availability of potential nest sites is known. We studied robins' nest sites in Białowieża National Park, eastern Poland, on three study plots (~30 ha each) in 2016–2019. Among all nests found (n = 165), the majority (118, ~72%) were found in tree holes, followed by ground nests (25, ~15%) and root-soil plates (22, ~13%). When the availability of cavities and root-soil plates is accounted for, it appears that robins preferred tree holes over plates. Robins appeared to be weakly selective in respect to tree species, preferring hornbeam Carpinus betulus, small-leaved lime Tilia cordata and Norway spruce Picea abies over other trees. Since both cavities and root-soil plates are superabundant in the Białowieża Forest, but scarce or absent in the heavily transformed robin breeding habitats of Western Europe (parks, orchards, hedgerows or managed forests), ground-nesting may predominate there simply due to these choice limits. In summary, our results provide a basis for understanding how original nest-site choices that evolved in natural, unmodified habitats can change when a species adapts to human-transformed habitats. [ABSTRACT FROM AUTHOR]

Although white stork Ciconia ciconia counts go back to the XIX century, making the species a model in population investigations, substantial gaps remain in the knowledge of its large-scale population dynamics. In particular, incomplete past estimates from the core breeding areas leave the long-term changes uncertain. In this paper, we provide the earliest estimation of population size and spatial distribution of the white stork in its main stronghold (Poland) to reconstruct the species long-term trends. Based on original survey data collected during the 2nd (1958, incomplete in Poland) and 3rd (1974, successful) International White Stork Census (IWSC) we compared stork numbers in a random sample of villages surveyed on both occasions. We applied linear models to estimate the population growth rate between 1958 and 1974 and to assess spatial variation in population change across the country. Finally, we collated worldwide stork numbers obtained from all IWSCs and discuss the long-term population trends in light of new data. The stork population in Poland in 1958 was estimated at 46,100 breeding pairs and the nationwide density at 14.7 pairs/100 km2. A strong decline (by 30.2%, 1.88% per year) was noted between 1958 and 1974 across Poland with prominent spatial variation reflecting differences in local densities. The strongest declines in absolute terms affected the most abundant populations in Eastern Poland. Our data show that in the mid-20th century, the stork population in Poland was close to the current level, but it experienced a massive decline during the 1960s–1980s. This decline was consistent with trends in the worldwide and regional European populations, contrary to earlier statements indicating limited, if any, changes in the core European area. Overall, our data expand knowledge on the long-term dynamics in the white stork numbers and show that even massive changes may easily go undetected if based on non-solid data. [ABSTRACT FROM AUTHOR]

The great tit Parus major inhabits various types of forests, yet it prefers deciduous forests. In the urbanized areas it is one of the commonest bird species, even where only isolated trees are present, which seems to be a relatively recent phenomenon. This paper presents results of a long-term study (2002–2015) of variation in reproductive performance (number of hatchlings, hatching success, number of fledglings, fledging success, breeding success and nest failure rate) in first clutches of two great tit populations nesting in two contrasting habitats: a mature deciduous forest and an urban parkland, in central Poland. This study shows a clear and sustained spatial pattern of variation where the forest population of great tits produced more hatchlings and fledglings per successful nests than the urban park site population. Breeding success and fledging success demonstrate a similar but slightly less obvious pattern, with higher values for the forest site than the urban parkland area occurring consistently in the vast majority of years. Also hatching success was generally slightly higher in the forest than in the urban park but did not show such a clear spatial pattern. Only the nest failure rate was higher in the forest than in the urban parkland. We suggest that caterpillar richness in the forest compared to the urban parkland is one of the key drivers of the observed differences in the breeding performance between the study habitats. We also found positive correlations between fledgling numbers and caterpillar abundance and between fledgling numbers and mean May temperatures in the forest, whereas neither breeding nor fledging success showed such correlations. In the urban parkland, fledgling numbers as well as fledging and breeding successes were positively correlated with mean May temperatures. The between-population variation we found probably reflects a more general difference between urban and forest populations of tits. [ABSTRACT FROM AUTHOR]

Alternative mating strategies, involving mating outside a social pair bond, have been studied intensively during the last few decades. However, we are still far from understanding what factors affect their frequencies in wild bird populations. In 2006–2011 we studied Eurasian Reed Warblers breeding in the nature reserve "Stawy Milickie" in SW Poland, and analysed the frequency of extra-pair paternity (EPP) and intra-specific brood parasitism (IBP). We genotyped a total of 786 nestlings from 259 nests. EPP offspring constituted 13.40% of all young (from 7.63% to 22.82% in different study years), and they were found in 21.62% of the broods (from 14.6% to 32.7% annually). The mean proportion of females with EPP young was 24.2% (from 16.2 to 41.7% annually). The proportion of EPP young in nests containing any EPP offspring ranged from 25% to 100% (on average 60%) and was not related to brood size. EPP young in one nest were sired usually by one or two males (92% of all cases), but we recorded one brood with three EPP fathers and one brood of four, where each young was sired by a different EPP male, and none by a social male. We found only one case of intra-specific brood parasitism (IBP). The brood with IBP constituted 0.39% of all examined broods, while the nestling that hatched from the dumped egg constituted 0.13% of all young whose parents were genotyped. We conclude that extra-pair paternity is a relatively common and regularly occurring alternative mating strategy in our study population of Reed Warblers, while intra-specific brood parasitism is extremely rare. [ABSTRACT FROM AUTHOR]

Many marsh birds, like bitterns or rails, are endangered species inhabiting only natural habitats and dependent exclusively on different types of emergent vegetation. In a changing environment, some of these habitat specialists are becoming more flexible, shifting their preferences by colonizing man-made habitats. We studied habitat selection by Little Bitterns (Ixobrychus minutus minutus) breeding in a fishpond landscape in south-eastern Poland. Applying a large-scale research approach, we examined several habitat features in order to predict the presence of the Little Bittern from a direct comparison of areas with and without breeding birds. Partial least squares (PLS) regression identified two components of several variables that explained 53% of the variation in the presence of the Little Bittern in a fishpond habitat. The occurrence of the Little Bittern was limited to high-quality patches of emergent vegetation, the height, width and area of which were all significantly greater in the area with breeding birds than in unoccupied patches. Patches with a highly variable edge line in the form of fringes or indentations were less favoured. An optimal water level throughout the breeding season was crucial for nest-site selection and ensured access to food. The heterogeneity of the pond dykes and pond canals positively predicted the presence of the Little Bittern by creating potential nesting or foraging sites. Interestingly, the proportion of bulrushes (Typha spp.) in the emergent vegetation patches had a negative effect on the presence of the Little Bittern. The main threat to this habitat‐sensitive species was the cutting of perennial emergent vegetation, in particular the Common Reed (Phragmites australis). [ABSTRACT FROM AUTHOR]

During the studies on the invertebrate fauna of the subterranean part of the "Wieliczka" Salt Mine in Wieliczka, Poland, the presence of many specimens of the dipteran species Meoneura obscurella (Fallén 1823) was observed. Organic remains and faeces related to the presence of mice (Mus musculus) were indicated as a potential food source for the insects. M. obscurella displays lecithotrophic viviparity (ovoviviparity), which has developed due to extremely harsh abiotic conditions and a lack of food. This is the first documented case of lecithotrophic viviparity within the fly family Carnidae. Based on the ability of this species to inhabit and reproduce in the conditions of the subterranean part of the "Wieliczka" Salt Mine, it is proposed to classify the species as a troglophile. The occurrence of Niptus hololeucus (Faldermann 1835), a species of beetle representing the family Ptinidae, was also confirmed in the subterranean part of the "Wieliczka" Salt Mine. [ABSTRACT FROM AUTHOR]

Analysis of the qualitative signature of fatty acids in tissues of organisms is an increasingly utilized tool in studies of trophic ecology in aquatic and terrestrial ecosystems. Here, we studied a colonial waterbird, the black-headed gull Chroicocephalus ridibundus, nesting in three colonies. We aimed to investigate whether fatty acid composition of its eggs is affected by the location of the colony (reflecting the spatial variation in habitat composition and, in turn, female diet at the time of egg formation), and the egg laying sequence (reflecting the temporal variation in female diet). We found that the composition of fatty acids in eggs of black-headed gulls differed among colonies, but not among subsequent eggs within the clutch. We interpret these results in the context of spatial differences in the diet of females breeding in different colonies and a lack of temporal variation in the diet of individual females. The pattern of the ratio of omega-3 to omega-6 fatty acids reflected the contribution of aquatic/terrestrial prey to their diet, and was consistent with the area of water courses around the colonies. High levels of omega-6:omega-3 can promote inflammation and thus lead to increased susceptibility to antigens. Further studies with prey sampling are required to reconstruct the diet composition of females during egg formation in more detail. [ABSTRACT FROM AUTHOR]

The Clouded Apollo, Parnassius mnemosyne is a charismatic West Palaearctic butterfly, threatened in some European countries and listed in Appendix IV of the Habitats' Directive. We investigated a large lowland population of the species inhabiting a complex of irregularly coppiced light forest and adjacent wet meadows in the anthropogenic landscape in the valley of the Narew river in NE Poland. A mark-release-recapture (MRR) method was used over 4 years to estimate population size, adult catchability, daily survival and lifespan. The beginning and length of the flight period (which lasted 4-6 weeks) differed over the years and was clearly related to weather conditions (temperature, sunshine) in April, i.e. the most important period for larval development. The seasonal population size varied from 555 to 942 adults. In contrast to some previous studies, the sex ratio turned out to be well balanced, although the catchability of males was significantly higher than that of females in each year. The quality of the wings deteriorated during the season in both sexes, but it was generally better in the case of females, which indicates that they are less active. Inter-seasonal variation in the lifespan (6.36-12.45 days) is more difficult to interpret, but it is worth noting that individuals lived the longest in the coldest and least sunlit flight period. The temporal fragmentation index (i.e. the ratio of flight-period length to adult lifespan) also varied (3.37-5.97) but was generally relatively low, which suggests that there is no threat of reduction of the effective population size at the moment. Nevertheless, the investigated population may be at risk of decline due to the observed intensification of meadow use and especially the possible conversion of grasslands into cornfields. [ABSTRACT FROM AUTHOR]

The stone moroko (Pseudorasbora parva) is an invasive species which spreads rapidly in European water bodies and occupies free ecological niches. In the years 2019-2020, monthly analyses of its population structure were carried out in the Wardynka River (western Poland), determining the age, size (TL and SL), body weight, growth, Fulton's condition factor, and the parameters of the length-weight relationship. In addition, quantitative descriptions of the parasite communities were made. End-point PCR was used to verify the presence of Sphaerothecum destruens in the fish. The age structure of the population was dominated by fish at the age of 1+ to 3+, and the maximum age was 5 +. The TL of the fish ranged from 2.50 to 10.60 cm (average 6.24 cm), SL from 2.10 to 9.50 cm (average 5.20 cm), and body weight from 0.15 to 11.43 g (average 2.74 g). The average body weight and length of males were higher than in females. The average Fulton's condition factor for the whole sample was 1.44 ± 0.24 and was similar for both sexes. The slope of the regression line (b > 3) indicates an allometric relationship between the length and weight of fish of both sexes. Back-calculated estimates of standard length fitted the von Bertalanffy growth function, although Taylor's criterion showed that the asymptotic length (Linf) was overestimated. Comparison of the von Bertalanffy growth function parameters revealed differences between sexes. The presence of parasites not previously recorded in stone moroko in Poland was confirmed: Dactylogyrus squameus, Phyllodistomum elongatum, P. folium, Posthodiplostomum cuticola (metacercaria), and Bivalvia gen. sp. (glochidia). Electrophoresis of the end-point PCR product did not reveal any signs of amplification for either of the primer sets used. S. destruens was not detected in any of the analysed samples of stone moroko. [ABSTRACT FROM AUTHOR]

Water level appears to be crucial for waterbirds, especially in the changeable conditions prevailing in river valleys. One of the best preserved Central European rivers is the Biebrza in north-eastern Poland, which seasonally overflows in spring, creating optimal habitats for various waterbirds. We examined a number of environmental factors which could strongly influence different foraging groups and bird assemblages with respect to water surface area and depth. Number of waterbirds peaked during the second half of March, when a large wave of geese and ducks stopped over there. The species diversity was the greatest in the first half of April, when more species arrived from their wintering grounds. We did not find any relationship between water depth and total abundance, but the former did significantly influence the numbers of some ecological feeding groups of waterbirds, i.e. diving omnivores, diving carnivores and surface carnivores. We assume that higher water level in a river valley is favourable to birds during their spring passage, because it creates areas of shallow floodwater that are intensively used by many different aquatic species. Owing to the well-preserved hydrological conditions and its full protection as a national park, the Biebrza valley not only offers optimal conditions for migratory waterbirds, but is also a good research area for studies of the phenomena taking place in avian communities during their migratory staging. [ABSTRACT FROM AUTHOR]

The black stork Ciconia nigra is a rare species of bird that inhabits old forests near wetlands. The early 21st century has brought a regress of its population in north-eastern Poland. We verified the assumption that an important reason for the observed changes was the colonization of the study area by white-tailed eagle Haliaeetus albicilla, because we observed a correlation between decreasing numbers of the black stork and increasing numbers of the eagle. Based on the long-term monitoring, we analyzed changes in the numbers and distribution of the black storks' nests and compared the colonization of the study area by the white-tailed eagle in the most extensive forest complex in Poland. We found 42 occupied territories of storks and no eagles in 1989 within the study area. In 2019, there were just 23 stork pairs, but the population of eagles increased to 13. We found a correlation between the rate of decline of the black storks population and the increase in the white-tailed eagles. In the first half of study period, storks' nests have been distributed randomly, after which they became clustered. The pattern of nests distribution was influenced by the increase in the population of the eagle over time, with this ensuring the aggregation of the nests of storks in places more distant from the nests of eagles. Similarly, the nearest neighbor distance of storks' nests was dependent on distances from the nests of eagles and the shares of territory accounted for by forests. We surmise that changes in the population size of storks were induced mainly by the growth of population of eagles. Storks avoided occupying nests less than 4.6 km from the eagles' nests. Our study suggests that the determining role can be played by fear of the predator. Overall, it must be concluded that the protection of top predators can affect other co-occurring species in unexpected ways. In the Augustów Forest (north-eastern Poland), the number of the black stork Ciconia nigra over 30 years has strongly declined and the distribution of its occupied nests has changed from almost solitary to clustered. The colonization of the study area by the white-tailed eagle Haliaeetus albicilla was a plausible reason for the observed changes. Storks avoided occupying nests less than 4.6 km from the white-tailed eagles' nests, which can be defined as a safety distance. The determining role can be played by the fear of the predator more than by direct predation. [ABSTRACT FROM AUTHOR]

Nesting habits of the digger wasp Lindenius albilabris (Fabricius, 1793) at two localities in Poland were studied. The female hunts nymphs or adults of plant bugs Lygus rugulipennis Poppius, 1911 and L. pratensis (Linnaeus, 1758), depositing up to 10 individuals per cell, depending on their size. Nests are built in a wide variety of sandy habitats, on dirt roads, and in wastelands. The nest consists of a 10–12 cm long main burrow and one to three cells. Males are usually found on flowers of wild carrots Achillea millefolium, Daucus carota, Peucedanum oreoselinum, Pimpinella sp. and Tanacetum vulgare. The nest kleptoparasite Metopia argyrocephala was recorded in nests of this species. The mature larva is first described in this study and its morphology is compared with other species of the genus. [ABSTRACT FROM AUTHOR]

Climate change and extreme weather events may be seen as an opportunity to help understand the mechanisms by which birds adjust their breeding parameters to environmental variability. In the breeding season of 2020, several factors, such as a prolonged drought period, a relatively warm winter with no snow cover, and a cold spring (the coldest May in Poland since 1991) affected many bird populations in Poland. The great tit Parus major tended to produce much smaller clutches, much fewer fledglings, and had very low breeding success, increasing with the progress of the breeding season in 2020, in contrast to the more typical breeding season characterised by average weather parameters in 2018. In light of the results obtained, we agree with the view that the phenotypic plasticity of the breeding parameters of the studied birds, such as phenology, may be insufficient to adjust to the upcoming extreme weather events. Additionally, further examining of the impact of extreme weather events on the breeding biology of animals is an important goal for future studies. [ABSTRACT FROM AUTHOR]

We hereby provide the first documented data on the occurrence of a viable Procambarus virginalis population in a nature reserve in Poland and the steps that were taken to prevent further introductions of the species in the country. To date, Poland represents the most north-eastward distribution area in Europe, where the species occurs in ecosystems with natural water temperature regimes. The ecological plasticity of P. virginalis and its obligate parthenogenetic reproduction make this crayfish an exceptional invader. The crayfish may have detrimental effects on the native invertebrates, amphibians, and fish, and alter the state of the entire ecosystem. Therefore, we investigated the presence of the species in the nature reserve of Pojezierze Łęczyńskie Landscape Park after a suspected P. virginalis individual was found by a local citizen. The nature reserve also includes an area designated to protect native amphibians and turtles. Our study revealed the presence of a thriving population of P. virginalis in the protected area and clear indications of its impact on native and invasive species, both in aquatic and terrestrial environments. If no action is taken, the species will likely expand to other water bodies across the country. An extensive sensibilization campaign allowed us to find additional invaded areas and significantly contribute to the effective ban of this and other invasive crayfish species from private and commercial online trade. Raising public awareness and banning invasive crayfish species trade is essential for successfully detecting and preventing further introductions. [ABSTRACT FROM AUTHOR]

Long-term research has become increasingly important in predicting ecological changes, although only a few studies have reported changes in amphibian communities over long time scales in urban areas. The main aim of the research was to determine the changes in the number and species composition of amphibian communities in small water bodies of two Olsztyn (NE Poland) settlements in the period between 1997 and 2015. The examined settlements are characterized by a high concentration of small water bodies and different degrees of urbanization. A decrease in the diversity index of reproducing amphibian communities was found between the years 1997 and 2015 at both settlements. Over the period of 18 years, one species – the northern crested newt – disappeared from both settlements, and another – the fire-bellied toad – disappeared from one of the two settlements. We demonstrate a significant relationship between the probability of occupancy of a water reservoir by fire-bellied toad, common frog, edible frog, and pool frog and the degree of isolation of these water reservoirs. Moreover, a decrease in the average number of species in a single water body and in the average values of diversity was also observed. The diversity of amphibian communities in water reservoirs depended mainly on the distance to the nearest water reservoir, the nearest building and the area of vegetation in the water reservoir. Available data suggests that the newly created water reservoirs play a positive role in the protection of amphibians in urban spaces, but the restoration of local amphibian communities is related to the degree of urbanization, and mostly applies to generalist species. [ABSTRACT FROM AUTHOR]

The impact of fish-eating birds on fishery has long been debated. It is therefore important that the arguments in this debate be scientifically based. The Great Cormorant Phalacrocorax carbo is a flagship example of a conflict species that has been well studied. In some areas, however, such as the southern Baltic estuarine lagoons, the Goosander Mergus merganser may be more abundant, exerting a potentially greater impact on fisheries. However, this aspect has not been well studied in this region, so this article is an attempt to fill this knowledge gap. Based on the digestive tract content of 23 Goosander drowned in gillnets in Poland, it was found that the most frequently consumed species was Ruffe Gymnocephalus cernua (70% of biomass), followed by Zander Sander lucioperca (13% of biomass), Perch Perca fluviatilis (9% of biomass) and Roach Rutilus rutilus (8% of biomass). Average Goosander numbers in the Vistula and Odra estuaries in 2011–2018 were 11,000 in winter, 4,500 in spring and 2,800 in autumn. These fish-eating ducks were found to consume 242 t of fish annually during this period, whereas at the same time fishermen caught an average of 4,400 t of fish. The species caught by both Goosander and fishermen were mainly Zander (32 t vs 189 t), Perch (21 t vs 668 t) and Roach (19 t vs 701 t). No negative impact of Goosander foraging in the winter preceding the fishery season was demonstrated for any of the above species (Zander R2 = 0.022; Perch R2 = 0.834; Roach R2 = 0.881). [ABSTRACT FROM AUTHOR]

The aim of this study was to determine the levels of Na, K, Ca, Mg, Fe, Zn, Cu, Pb and Cd in the muscle, liver and gills of roach (Rutilus rutilus) and perch (Perca fluviatilis) from three polymictic and eutrophic lakes in poor ecological condition in north-western Poland. Metals in the waters of the lakes, as well as in the muscle, gills and livers of fish, were determined by atomic absorption. Oxygen deficits in summer and high concentrations of Cd and Pb were responsible for the low water quality of the lakes studied. Perch and roach showed a potential to accumulate metals from the water (bioconcentration factor >1). The lowest concentrations of Na, Fe, Zn, Cu, Pb and Cd were found in the fish muscle. The highest concentrations of Cd and Pb were recorded in the liver of both species. Differences in metal concentration between the species were mainly due to significantly higher levels of Fe, Cu and Zn in the muscle of the roach than in the perch (p < 0.05). A portion of 100 g/day of roach or perch muscle can be a complementary source of elements essential to the human diet, because Dietary Reference Intakes were below 2% for Fe, 5% for Na, Ca and Cu, and 10% for K, Mg and Zn. With regard to Pb and Cd levels, consuming the muscle of these fish from the studied lakes should not pose a health risk (Acceptable Daily Intake less than 1%). [ABSTRACT FROM AUTHOR]

Egg size is an important determinant of offspring weight and survival. However, despite extensive research on factors affecting egg dimensions, causes of egg variation are not fully understood. Between 2000 and 2016 we studied a population of little bitterns in western Poland, and examined a total of 529 eggs from 88 clutches. Furthermore, we conducted an extensive literature search for data on clutch and egg size from other populations of the species to test hypotheses explaining the relationships between these variables and latitude. Little bitterns in western Poland laid big eggs but also produced large clutches compared to most other studied populations of the species. The ratio of largest to smallest egg calculated for egg volume was 1.75 for all studied eggs, and up to 1.35 within clutches, suggesting a huge variation between and within clutches in the studied population. Egg dimensions were highly intercorrelated, but egg size was not related to clutch size in the study population. The comparison of data from different populations of the species revealed that egg volume increased significantly with latitude and was positively correlated with clutch size. These results support the embryonic temperature hypothesis and clutch cooling rates hypothesis, but contradict the optimal egg dimensions hypothesis. [ABSTRACT FROM AUTHOR]

The Białowieża Forest is the only place in Europe where the full development cycle of temperate forest can be observed on a large scale, starting from the regeneration phase until the terminal (decay) phase. At present, the terminal phase is not observed in most forests in Europe due to management practices such as logging and removal of dead trees. In this study, we analysed plant-dwelling spider communities in three developmental phases (optimal, terminal and regeneration) of a primeval oak-lime-hornbeam stand in the Białowieża National Park. Spiders were sampled from May to October in 1998 and 1999 using a sweep net. A total of 3693 spider individuals from 13 families were collected, of which 2278 were identified at the species level. In total, 63 spider species were recorded (including species identified based only on juvenile individuals): 33 in the optimal phase, 36 in the terminal phase, and 41 in the regeneration phase. The composition of plant-dwelling spider communities in three developmental phases was similar. Among adult individuals, Linyphia triangularis (Clerck, 1757) was the most numerous species on the plot in the optimal phase, whereas Bathyphantes nigrinus (Westring, 1851) was the most abundant species on the plots in the terminal and regeneration phases of the stand development. Significantly higher species diversity (calculated for the whole study period) was found in the regeneration and optimal phases compared to the terminal phase. We revealed no difference in the abundance, species richness, and species diversity (calculated per sample) between the analysed plots. On the other hand, each of the developmental stages was characterised by a significant proportion of exclusive species, even though they were represented by a few individuals. This suggests that the presence of different forest stages in a given area favours higher species diversity. [ABSTRACT FROM AUTHOR]