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Long-term changes of mollusc assemblages in bottom sediments of small-isolated lakes of different trophic state

Kołodziejczyk A., Lewandowski K., Stańczykowska A.

Polish Journal of Ecology

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2009

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Vol. 57, nr 2

331-339

EN

It is a common view that increase of the trophic state of lakes has a negative effect on littoral invertebrate macrofauna, molluscs among them. However, the available data are often contradictory, and the decline of particular species is often observed only at a very pronounced raise in trophic state. The aim of this work was to present the changes of the composition and abundance of bottom malacofauna taking place during last 30 years in five small (area from 0.12 to 1.74 km[^2]), mainly shallow (mean depth from 3.7 to 11.8 m) lakes of different trophic state (eutrophic and mesotrophic), connected by a small river (Masurian Lakeland, Northeastern Poland). The research were conducted in years 1997 and 2006 and were compared with published data, collected in 1976. The trophic state of the lakes studied was still constant during the period of investigations. In the studied lakes the decrease of number of bottom mollusc species was observed in subsequent years. The previously recorded there alien, invasive species, Potamopyrgus antipodarum (J.E. Gray, 1843) and Lithoglyphus naticoides (C. Pfeiffer, 1828) also disappeared. Dreissena polymorpha (Pallas, 1771) remained the dominant species in most of the lakes. These changes were recorded in four eutrophic lakes as well as inone mesotrophic lake. The decline of the species in individual lakes didn't follow any regularity. Some mollusc species disappeared and value of similarity index between malacocenoses in these lakes decreased. It seems, that the trophic state was not the cause of disappearance of some mollusc species from the studied lakes. However, the effect of frequent anoxia in littoral zone related to eutrophication was raised up as the possible cause. The decline is of long-term character, probably resulting from small size and relative isolation of the lakes, which impede their recolonisation.

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Impact of the invasive species Elaeagnus angustifolia L. on vegetation in Pontic desert steppe zone (Southern Ukraine)

Sudnik-Wójcikowska B., Moysiyenko I., Slim P., Moraczewski I.

Polish Journal of Ecology

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2009

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Vol. 57, nr 2

269-281

EN

The Irano-Turanian species - Russian olive (Elaeagnus angustifolia L.) - is one of most commonly planted tree in the shelterbelts in southern Ukraine. The consequences of introduction of the species from windbreaks, into areas of different land use in west and central Pontic desert steppe zone are evaluated. The above steppe is unique on a European scale and exists only in some parts of the Black and Azovian Sea coasts. In recent years, the socio-economical crisis in Ukraine (less intensively cultivation, as well as limited grazing) has been responsible for the intensification of the spread of alien tree species outside the windbreaks. Studies were conducted in Kherson Region, in the immediate vicinity of the Black Sea Biosphere Reserve, where the presence of aliens is undesirable. The analysis of phytosociological material (48 releves with and without Russian olive) collected from areas of different land use type and limited human pressure (as abandoned field, former intensively grazed solonetz and extensively grazed desert steppe vegetation) show that E. angustifolia can impede the regeneration of the desert steppe. The species creates favourable conditions for the growth of geographically and ecologically alien nithrophilous weeds.

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Ten years of change in ground-layer vegetation of European beech forest in the protected area (Ojców National Park, South Poland)

Łysik M.

Polish Journal of Ecology

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2008

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Vol. 56, nr 1

17-31

EN

Long-term changes in ground-layer vegetation of unique stand of Carpathian beech forest Dentario glandulosae-Fagetum considered partly as a natural succession due to climatic changes and partly as a response to canopy dynamics, were investigated in the Ojców National Park (South Poland). Species composition and structure of the herb layer in the permanent research area were compared in 1993 and after ten years. About 77% of the study area was changed in this period, but the spatial pattern of distribution and intensity was highly mosaic. The mean intensity of changes calculated according to formula (1) derived from changes in percent cover of species was 42%. Herb cover decreased by about 15%, probably due to the rapid development of natural recruitment of trees in the study area (48% of area was covered by dense tree recruitment). In the same time the number of plant species and vegetation types (homogeneous vegetation patches of the size at least 1m2, that differed from neighbouring patches in species composition and/or species share) increased substantially. It is probably due to greater variation of light condition in ground layer created as a result of canopy gaps dynamics (the area of windthrow mounds in the study area increased approximately eight times between 1993 and 2003). There was a significant decline of species typical for beech forests, especially of vernal geophytes like Dentaria glandulosa W.K. and Isopyrum thalictroides L. Although it is too early to predict any directional changes, it is possible that the beech forest community will change into the Tilio-Carpinetum association in some parts of study area. Nowadays the expansion of invasive alien species Impatiens parviflora DC. is the great threat to the forest vegetation of the protected study area and the Ojców National Park. This species in 10 years managed to displace native species in 3% of the study area. The drastic decrease in herbaceous plants cover connected with increase in tree seedlings and saplings, systematic decline of vernal geophytes and typical beechwood species, diversification of ground vegetation structure and composition, and finally occurrence of non-native invasive plant species inform about highly dynamic nature of climax beech forests and generally of temperate forests. Changes are induced probably by both changing climate and overstorey dynamics.

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Dispersal - limited biodiversity of tropical insular streams

Covich Alan P.

Polish Journal of Ecology

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2006

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Vol. 54, nr 4

523-547

EN

Numerous species are adapted for colonization of insular fresh waters by using different mechanisms of active and passive dispersal, especially among oceanic islands at low latitudes. Over time, similar animal communities have assembled in many tropical streams and rivers on isolated islands. These freshwater communities are characterized by a relatively low number of species of fishes, decapods, gastropods and insects that typically have complex life cycles including passive, long-distance dispersal. These species often disperse during marine phases with drifting larvae or by rafting and aerial transport of resistant, dormant stages. Active dispersal is sometimes effective for relatively short-distance movements from one island.s streams to another island's nearby drainage basin within an archipelago (a "stepping-stones" dispersal pattern). Identifying distinct differences among aquatic communities on "true oceanic" islands of different ages and geologic histories requires a longterm biogeographic perspective including the degree of spatial isolation of populations and differences in rates of speciation. Consequently, the total biodiversity of insular streams is a complex combination of dispersal from multiple sources of species from continents and other islands, as well as evolution of new endemics. Recolonization of streams following natural disturbances and the impacts of introduced species result in dynamic changes in species accumulation and turnover in these insular freshwater ecosystems. Analysis of dispersal to islands provides general perspectives on managing fragmented habitats, especially the effects of invasive species that also shed light on factors affecting the equilibrium composition of animal communities in island-like ecosystems on continents.