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Von 1995 bis 1998 wurde die Cladoceren- und Ostracodenfauna des eutrophen Feldungelsees nördlich Osnabrück untersucht. Die Anzahl der Cladocerenarten ist gegenüber einer früheren Untersuchung auf 39 gestiegen. Ceriodaphnia laticaudata, Megafenestra aurita und Simocephalus exspinosus v. congener traten erstmalig im See auf. Die zwei Daphnia-Arten aus Nordamerika, D. ambigua und D. parvula, bewohnen weiterhin den See. 1995 wurden die jahreszeitliche Verbreitung und die Sexual perioden untersucht. Bei den meisten Cladocerenarten wurde Monozyklie beobachtet, 3 Arten traten dizyklisch auf. 17 Muschelkrebsarten wurden nachgewiesen, die für diese Gegend und diesen Lebensraum charakteristisch sind.
Global landscapes are changing due to human activities with consequences for both biodiversity and ecosystems. For single species, terrestrial mammal population densities have shown mixed responses to human pressure, with both increasing and decreasing densities reported in the literature. How the impacts of human activities on mammal populations translates into altered global density patterns remains unclear. Here we aim to disentangle the effect of human impacts on large-scale patterns of mammal population densities using a global dataset of 6729 population density estimates for 468 mammal species (representing 59% and 44% of mammalian orders and families). We fitted a mixed effect model to explain the variation in density based on a 1-degree resolution as a function of the human footprint index (HFI), a global proxy of direct and indirect human disturbances, while accounting for body mass, trophic level and primary productivity (normalized vegetation index; NDVI). We found a significant positive relationship between population density and HFI, where population densities were higher in areas with a higher HFI (e.g. agricultural or suburban areas – no populations were located in very high HFI urban areas) compared to areas with a low HFI (e.g. wilderness areas). We also tested the effect of the individual components of the HFI and still found a consistent positive effect. The relationships remained positive even across populations of the same species, although variability among species was high. Our results indicate shifts in mammal population densities in human modified landscapes, which is due to the combined effect of species filtering, increased resources and a possible reduction in competition and predation. Our study provides further evidence that macroecological patterns are being altered by human activities, where some species will benefit from these activities, while others will be negatively impacted or even extirpated.
In West African savannas, human land use affects the density of woody species seedlings and saplings (juveniles) by altering the state of the physical, chemical, and biological characteristics of the land resulting in different land-cover types. We determined juvenile densities of 25 characteristic woody savanna species on non-arable sites, in fallows and in a protected area (in total 39 plots), and analyzed the influence of land use on juvenile densities. We further related the influence of land use on juvenile densities to 23 environmental parameters describing soil properties and vegetation structure. Soil acidity, particle size distribution of the soil, and vegetation structure differed between land-cover types. In terms of human impact, we detected five groups of species responding similarly to land use. Although we detected significant differences in soil properties, their direct effects on juvenile densities are less pronounced than their indirect effects. By altering the availability of resources, soil properties affect height and cover of all plants growing in the surrounding of a young woody plant, increasing the competition for light, water and nutrients during the establishment and initial growth. These effects are intensified by human land use and vary between land-cover types.
Wir untersuchten eine Kolonie der Brückenspinne Larinioides sclopetarius (Clerck, 1757) an einem Strassendamm im Innenhafen von Duisburg. Die Studie fand zwischen März und Oktober 2004 statt. Die mittlere Populationsdichte über alle Größenklassen betrug 26,2 Ind./qm, das absolute Maximum wurde im Juli festgestellt (71,3 Ind./qm). Die kleinsten Juvenilstadien fanden wir hauptsächlich von Juni bis Oktober, mit einer maximalen mittleren Dichte von 30,9 Ind./qm im Juli, so dass man auf den Sommer als Schlupftermin schließen kann. Große Männchen und Weibchen gab es bereits vereinzelt im Frühjahr, allerdings wurden die höchsten Abundanzen (mit mehr als 3 Ind./qm je Geschlecht) im Sommer und Herbst erreicht. Das durchschnittliche Geschlechtsverhältnis der adulten Spinnen lag über die gesamte Untersuchungszeit gesehen bei 1:1,2 (männl.:weibl.). Es werden einige Vergleiche mit anderen Araneiden, darunter solitäre und soziale Arten, gezogen.
Climate change is influencing some environmental variables in the Southern Ocean (SO) and this will have an effect on the marine biodiversity. Peracarid crustaceans are one of the dominant and most species-rich groups of the SO benthos. To date, our knowledge on the influence of environmental variables in shaping abundance and species composition in the SO’s peracarid assemblages is limited, and with regard to ice coverage it is unknown. The aim of our study was to assess the influence of sea ice coverage, chlorophyll-a, and phytoplankton concentrations on abundance, distribution and assemblage structure of peracarids. In addition, the influence of other physical parameters on peracarid abundance was assessed, including depth, temperature, salinity, sediment type, current velocity, oxygen, iron, nitrate, silicate and phosphate. Peracarids were sampled with an epibenthic sledge (EBS) in different areas of the Atlantic sector of the SO and in the Weddell Sea. Sampling areas were characterized by different regimes of ice coverage (the ice free South Orkney Islands, the seasonally ice-covered Filchner Trough and the Eastern Antarctic Peninsula including the Prince Gustav Channel which was formerly covered by a perennial ice shelf). In total 64766 individuals of peracarids were collected and identified to order level including five orders: Amphipoda, Cumacea, Isopoda, Mysidacea, and Tanaidacea. Amphipoda was the most abundant taxon, representing 32% of the overall abundances, followed by Cumacea (31%), Isopoda (29%), Mysidacea (4%), and Tanaidacea (4%). The Filchner Trough had the highest abundance of peracarids, while the South Orkney Islands showed the lowest abundance compared to other areas. Ice coverage was the main environmental driver shaping the abundance pattern and assemblage structure of peracarids and the latter were positively correlated with ice coverage and chlorophyll-a concentration. We propose that the positive correlation between sea ice and peracarid abundances is likely due to phytoplankton blooms triggered by seasonal sea ice melting, which might increase the food availability for benthos. Variations in ice coverage extent and seasonality due to climate change would strongly influence the abundance and assemblage structure of benthic peracarids.