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The relationship between macrobenthic communities and environmental parameters in the Oum Er Rbia estuary was investigated during the summer season. Salinity, temperature, dissolved oxygen and sediment characteristics varied throughout the estuary. Significant spatial differences in the macrobenthic community structure and composition were found along the estuarine gradient, however salinity and sediment characteristics seemed to be the major factors controlling the differences in the assemblages' composition. Nevertheless, each assemblage was found in a particular physico-chemical environment and had a specific species composition depending on environmental conditions. A total of 30 macrobenthic taxa were identified, most of which were typical of brackish and marine waters. Species richness ranged from 1 to 21 species, with an average of 6.64 ± 6.02 species, whereas abundance ranged from 1 to 2501 indiv., with an average of 288.73 ± 736.81 indiv. Diversity values were generally low (< 3) due to the high dominance of few species. Cerastoderma edule was most numerous comprising 70.34% of the total number specimens gathered, followed by Hediste diversicolor (7.43%). Three species communities were identified: The Melita palmata community lived in the lower section of the river with a stronger marine influence and a sandy bottom. The middle section was occupied by the C. edule community on sandy-muddy substrates and included two sub-communities dominated by M. palmata and H. diversicolor. The upper section with a muddy substrate was the habitat of the H. diversicolor community and was also characterized by the lowest numbers of species and individuals in the entire Oum Er Rbia estuary.
Rehabilitation of river beds is sometimes necessary, particularly when a substantial amount of bottom sediment causes unnaturally slow water flow. However, it is difficult to predict whether such procedures will negatively affect biodiversity and species composition of organisms inhabiting these sites. The effects of such procedures were analysed in the Krąpiel river in northwestern Poland. It was postulated that dredging would not reduce Heteroptera diversity, but would alter the habitat significantly and create lotic habitats for rheophilous species. It was also postulated that conditions would become less favourable for taxa preferring a bottom with accumulated mud and abundant vegetation. According to our results, dredging did not significantly affect species diversity of Heteroptera, but did cause an increase in abundances of several species. Dredging increased the number of available habitats, which were mainly inhabited by abundant pioneer species. Aquarius najas, Aphelocheirus aestivalis, Plea minutissima, Sigara falleni, Notonecta glauca, Iliocoris cimicoides and Gerridae were most successful in recolonizing the sites after dredging. CCA showed that detritus and the effects of dredging were crucial to the distribution patterns of heteropteran species in this river.
Grazing by large mammals can affect small-mammal populations by modifying the ground-layer vegetation, which provides them with food and shelter. The aim of this study was to investigate the impact of semi-domesticated reindeer grazing on smallmammal abundance in boreal forests/subarctic tundra ecosystems in a large-scale exclosure experiment in northernmost Finnish Lapland. In our experiment spanning four years, reindeer grazing affected the abundance of arvicoline voles, which were less abundant in grazed areas. This was probably due to a reduction in the abundance and height of bilberry, an important forage plant for both voles and reindeer. Changes in ground-layer vegetation affected the general condition of bank voles, which had significantly lower body mass in grazed areas. The abundance of insectivorous shrews was also reduced by grazing, probably due to a reduction in ground-dwelling invertebrates as an indirect effect of changes in the composition of ground-layer vegetation. A grazing-induced reduction in small mammal abundance can have far reaching ecological consequences for small-mammal population dynamics as well as mammalian and avian predators depending on small mammals as food.
Competitive intraguild interactions can modify the spatial and temporal territory use of predators, e.g., this phenomenon was reported among species of owls (Strigidae). This study made use of owl guild present in fragmented forests in southern Poland to investigate how the occurrence of the dominant Ural owl affects the territory distribution of subordinate (in descending order): tawny owl, boreal owl and pygmy owl. Surveys carried out in 2014–2015 showed that the tawny owl decreases in density and the distances between its territories increase in sympatry with Ural owl. The tawny owl increases in abundance during the non-breeding season, in particular in sympatry with the Ural owl, where young tawny owls try to settle within territories of the Ural owl. The distribution of the boreal owl territories was found to be random with respect to the tawny owl, but territories were clustered in space with the Ural owl territories, which suggests that the boreal owl distribution tends to follow the availability of suitable nesting places rather than the avoidance of the tawny owl. The distribution of the pygmy owl territories was random with respect to the Ural owl, but clumped with respect to the tawny owl, as both species occupied fir-spruce stands avoided by the Ural owl. In summary, this study broadens the basic knowledge about spatio-temporal relations within the owl guild by showing that the occurrence of the dominant Ural owl is a substantial factor in shaping the distribution of owls in fragmented forests.
The common sandpiper is a small wader showing no sexual dimorphism in plumage and some dimorphism in size. Discriminant function analysis was applied to a set of morphometric traits of birds captured in Poland during migration. In total, 247 males and 111 females were measured and sexed molecularly. On average, females were larger in all measurements than males. The most sexually-dimorphic trait was wing length. Individuals with wing shorter than 111 mm were males and those with wing longer than 117 mm were females. These values are based on a large sample of individuals sexed molecularly and better describe the range of wing size characteristic of each sex compared with previously published works, where common sandpipers with wings longer than 115 mm were sexed as females. The best discriminant function included wing and tarsus plus toe lengths. The jackknife crossvalidation showed that this equation allowed for correct sexing of 77.1% of birds (87.5% of males and 54.1% of females). When identifying birds with this discriminant function, the values smaller than -0.33 indicate males, while greater than 1.26 indicate females. This allows for correct sexing of 95% of birds of each sex.
We studied the responses of red squirrels, Sciurus vulgaris, to food supplementation and avian predation risk during two winters in Finland, when the level of natural food production, spruce seeds, varied markedly. We performed an open experiment with 6 replicates in the landscape where squirrel signs were counted near a feeding station and/or active predator nest and control site. Within each site, we counted squirrel snow-tracks and feeding-signs and checked the usage of two nest-boxes. We observed that during the winter when natural food was less plentiful, red squirrel snow-tracks decreased at sites with predator. The same was observed, only less clearly, during the winter with more natural food. Food supplementation had no obvious effect. We conclude that predators have a clear effect on red squirrels in winter. Furthermore, in situations where a species is specialized in using fluctuating amounts of natural food resources, the role of artificial food supplementation may remain unclear.
The red squirrel (Sciurus vulgaris) is an arboreal species, relatively common in mixed, deciduous and coniferous forests and in urban parks. From autumn to early spring the main diet of red squirrels is seeds in closed conifer cones. In this study, we investigated characteristics of a habitat in western Poland where red squirrels were feeding on Scots pine (Pinus sylvestris). Understory cover, number of tree species, distance to an open area, distance to the nearest great spotted woodpecker (Dendrocopos major) anvil, and size of ten randomly selected Scots pine trees were measured on 70 transects. We used binary logistic regression to test which forest habitat parameters affected the presence of feeding signs of red squirrels. Feeding signs of red squirrels were found from sites close to forest edges with less understory cover, higher tree-species richness and larger size of trees. Red squirrels did not avoid sites close to great spotted woodpecker anvils. We conclude that forest stand structure is important for red squirrel feeding site occurrence, but red squirrels do not avoid close contact to open areas.
The objective of the study was to investigate the taxonomic structure and spatial distribution of ciliate communities, and to identify the environmental factors determining the taxonomic structure of the assemblages. Additionally, we compared ciliate communities inhabiting ponds on King George Island (Antarctica) with those on other islands of the maritime Antarctic. The taxonomic richness, abundance and biomass of ciliates in microbial mats varied among ponds increasing with their eutrophication level. As the level of eutrophication increased, there was a decrease in the abundance of predatory and omnivorous ciliates and a decrease in that of algivorous taxa. The canonical correspondence analyses of the spatial distribution of ciliates showed that all environmental variables together explained 76% of the total variance. The Monte Carlo permutation test showed that dissolved orthophosphates, nitrate and total organic carbon had the most significant effect on the distribution of ciliates. The proportions of individual functional groups of ciliates varied among ponds. The proportion of heterotrophic taxa increased with the trophic state of the ponds, while the proportion of mixotrophic taxa decreased.
The latitudinal diversity gradient predicts higher species richness at lower latitudes. Here, we utilize the data from a long-term monitoring with malaise traps to analyse if spider communities in Sweden are affected by geographic gradients and if these effects hold independent of forest type. The species richness and the effective number of species in spider communities were not significantly related to the latitudinal gradient. The effective number of species and the taxonomic distinctness of spider communities were related to longitude, with a higher number, but fewer related species in western parts of Sweden. The species and family composition were significantly related to latitude independent of forest type, with a dominance of Linyphiidae individuals and species in the north. Our study demonstrates the suitability of malaise trap sampling to contribute to a better understanding of local spider communities, as several rare and locally new species were recorded in this study.
The return of apex predators re-shape population densities of their prey species, creating conflicts and challenges for the conservation and management of both predator and prey populations. The population of white-tailed eagles (Haliaeetus albicilla) in the Baltic Sea has grown rapidly since the 1980s after a previous population collapse, causing growing predation pressure on its prey species. However, little is known about variation in the prey use in the landscape or changes in time. We provide detailed information about the diet of the white-tailed eagle along landscape-scaled gradients and about temporal changes in their diet over 25 years. We used an extensive data set with 7700 identified prey remains collected during the breeding season on the Åland Islands (Finland) 1985–2010. The results support the view of the white-tailed eagle as an opportunistic hunter, preying on the most available prey and switching to other prey when the availability changes.