Search results for "Arctic"
showing 10 items of 565 documents
Die Ölblumensymbiosen - Parallelismus and andere Aspekte ihrer Entwicklung in Raum and Zeit1, 2
2009
The oil-bee/oil-flower relationships: parallelism and other aspects of their evolution in space and time A survey is given of our present knowledge and existing hypotheses concerning the biogeography, history, and phylogeny of plant taxa yielding fatty oil as a floral reward, and of the bee genera involved in their pollination. Four syngenetic complexes of the symbiosis arose convergently: The neotropical, the paleotropical, the holarctic, and the capensic complex. On the basis of the mutual structural adaptations of bees and flowers it is concluded that, in addition, parallelism within related groups as a result of a common tendency to develop the respective organs, has played an important…
Fine-grain beta diversity in Palaearctic open vegetation: variability within and between biomes and vegetation types
2021
Aims: To quantify how fine-grain (within-plot) beta diversity differs among biomes and vegetation types. Study area: Palaearctic biogeographic realm. Methods: We extracted 4,654 nested-plot series with at least four different grain sizes between 0.0001 m² and 1,024 m² from the GrassPlot database spanning broad geographic and ecological gradients. Next, we calculated the slope parameter (z-value) of the power-law species–area relationship (SAR) to use as a measure of multiplicative beta diversity. We did this separately for vascular plants, bryophytes and lichens and for the three groups combined (complete vegetation). We then tested whether z-values differed between biomes, ecological-physi…
Scale-dependent plant diversity in Palaearctic grasslands: a comparative overview
2016
Here we present an extensive overview of plant diversity values in Palaearctic grasslands for seven standard grain sizes from 0.0001 to 100 m². The data originate from 20 studies, including the Field Workshops of the Eurasian Dry Grassland Group (EDGG), ranging geographically from Spain in the west to Siberia in the east, from Sicily in the south to Estonia in the north and from the sea coast up to 3100 m a.s.l. The majority of data is from dry grasslands (Festuco-Brometea, Koelerio-Corynephoretea, Cleistogenetea squarrosae), but there are also some mesic, wet, saline, acidic, alpine and Mediterranean grasslands included. Among others, we compiled data from 1795 1-m², 1109 10-m² and 338 100…
Soil microbial and microfaunal communities and organic matter quality in reindeer winter and summer ranges in Finnish subarctic mountain birch forests
2008
Abstract Reindeer husbandry has significant influences on the aboveground plant communities and the structure of the mountain birch forests in the Fennoscandian subarctic. We investigated how the reindeer-mediated aboveground changes affect soil microbial and microfaunal communities and enzymatic activities. We hypothesized that in areas with intensive summer browsing by reindeer, the carbon flow to belowground is reduced, but the carbon substances are more readily degradable. This is likely to influence both the abundance and the trophic structure of microbial and microfaunal communities. However, despite large differences in the vegetation, the reindeer ranges did not differ in the amount…
Synthesis of Oxetane-Functional Aliphatic Polyesters via Enzymatic Polycondensation
2012
Synthesis, characterization, and thermal properties of a series of oxetane-functional aliphatic polyesters are investigated. The incorporation of the acid-sensitive 3,3-bis(hydroxymethyl)oxetane (BHMO) into polymers is achieved by using the enzyme CALB (Candida antarctica Lipase B) as a catalyst. This mild synthetic strategy provides well-defined, oxetane-functional polyesters. The enzymatic polycondensation allows for the synthesis of a series of aliphatic polyesters containing various ratios of the difunctional monomers sebacic acid, 1,8-octanediol, and BHMO with molecular weights between 5000–9800 g mol−1 and polydispersity indices (Mw/Mn) in the range of 1.25 and 1.92. Furthermore, cros…
Benthic resources are the key to Daphnia middendorffiana survival in a high arctic pond
2011
Summary 1. Shallow arctic lakes and ponds have simple and short food webs, but large uncertainties remain about benthic–pelagic links in these systems. We tested whether organic matter of benthic origin supports zooplankton biomass in a pond in NE Greenland, using stable isotope analysis of carbon and nitrogen in the pond itself and in a 13C-enrichment enclosure experiment. In the latter, we manipulated the carbon isotope signature of benthic algae to enhance its isotopic discrimination from other potential food sources for zooplankton. 2. The cladoceran Daphnia middendorffiana responded to the 13C-enrichment of benthic mats with progressively increasing δ13C values, suggesting benthic feed…
Redistribution of total reactive nitrogen in the lowermost Arctic stratosphere during the cold winter 2015/2016
2021
During winter 2015/2016 the Arctic stratosphere was characterized by extraordinarily low temperatures in connection with the occurrence of extensive polar stratospheric clouds. From mid of December 2015 until mid of March 2016 the German research aircraft HALO (High Altitude and Long–Range Research Aircraft) was deployed to probe the lowermost stratosphere in the Arctic region within the POLSTRACC (Polar Stratosphere in a Changing Climate) mission. More than twenty flights have been conducted out of Kiruna/Sweden and Oberpfaffenhofen/Germany, covering the whole winter period. Besides total reactive nitrogen (NOy), observations of nitrous oxide, nitric acid, ozone and water were used f…
Contribution to the Antarctic benthos: bathymetric and biogeographical patterns in Antarctic benthic hydroids and diversity of the genus Symplectoscy…
2019
Los hidrozoos bentónicos están considerados un importante grupo zoológico del bentos antártico. Durante los últimos años, nuestro conocimiento a cerca de su biología y ecología se ha incrementado gracias a los diferentes estudios que se han publicado. Sin embargo, a pesar de toda la nueva información adquirida todavía hay algunas cuestiones que están en debate pero que podrían ser resueltas utilizando de manera correcta toda la información recopilada. En el presente estudio se recopiló y actualizó la información sobre la biogeografía y ecología de los hidrozoos bentónicos para resolver algunas cuestiones biogeográficas como la división Este-Oeste del océano Antártico.…
Regions gelades: Àrtic i Antàrtica en el nou mileni
2012
Xerrada sobre l'àrtic i l'antàrtic en el nou mil · lenni donada en el congrés sobre lleis regionals i internacionals realitzat a València del 13 al 15 de setembre.
Witnessing and measuring the impacts of cryosphere changes in the High Arctic
2016
International audience