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821.
822.
The Science of Nature - 相似文献
823.
Prof. Dr. Th. von Kármán 《Die Naturwissenschaften》1916,4(33):489-494
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826.
Gergely Hegyi Eszter Szöllősi Susanne Jenni-Eiermann János Török Marcel Eens László Zsolt Garamszegi 《Die Naturwissenschaften》2010,97(6):567-576
The information content of a sexual signal may predict its importance in a multiple signal system. Many studies have correlated
sexual signal expression with the absolute levels of nutrient reserves. In contrast, the changes of nutrient reserves associated
with signal expression are largely unknown in the wild due to technical limitations although they are important determinants
of signal information content. We compared two visual and eight acoustic sexual traits in male collared flycatchers to see
whether the nutritional correlates of expression predict the role of the signal in sexual selection. We used single point
assays of plasma lipid metabolites to estimate short-term changes in nutritional state in relation to sexual trait expression
during courtship. As a measure of sexual selection, we estimated the relationship with pairing latency after arrival in a
4-year dataset. Males which found a mate rapidly were characterized by large wing and forehead patches, but small song strophe
complexity and small figure repertoire size. Traits more strongly related to pairing latency were also more closely related
to changes in nutrient reserves. This indicates a link between signal role and information content. Small wing patches and,
surprisingly, complex songs seemed to indicate poor phenotypic quality and were apparently disfavoured at mate acquisition
in our population. Future studies of the information content of sexual traits, especially dynamic traits such as song, may
benefit from the use of plasma metabolite profiles as non-invasive indicators of short-term changes in body condition. 相似文献
827.
Luis Lassaletta Héctor García-Gómez Benjamín S. Gimeno José V. Rovira 《Environmental Science & Policy》2010,13(5):423-433
The European Union Water Framework Directive (WFD) aims to achieve the “good status” of waters by 2015, through monitoring and control of human impacts on “bodies of surface water” (BSWs), discrete elements for quality diagnosis and management. Headwater streams, however, are frequently neglected as they are not usually recognised as BSW. This poses limitations for the management of river catchments, because anthropogenic impacts on headwaters can constrain the quality of downstream rivers. To illustrate this problem, we compared nitrate levels and land use pressures in a small agricultural catchment with those recorded in the catchment in which it is embedded (Ega), and in the Ebro River Basin (NE Spain) comprising both. Agriculture greatly influenced water nitrate concentration, regardless of the size of the catchments: R2 = 0.91 for headwater catchments (0.1–7.3 km2), and R2 = 0.82 for Ebro tributary catchments (223–3113 km2). Moreover, nitrate concentration in the outlet of a non-BSW small river catchment was similar to that of the greater downstream BSW rivers. These results are of interest since, despite representing 76% of the length of the Ega catchment hydrographical network, only 3.1% of the length of the headwater streams has been identified as BSWs. Human activities affecting headwater streams should therefore be considered if the 2015 objective of the WFD is to be achieved. 相似文献
828.
Efficiency of white lupin in the removal of mercury from contaminated soils: Soil and hydroponic experiments 总被引:1,自引:0,他引:1
Pilar Zornoz Roc′?o Mill′an M. Jos′e Sierr Almudena Seco Elvira Esteban 《环境科学学报(英文版)》2010,22(3):421-427
This study examined the ability of the white lupin to remove mercury (Hg) from a hydroponic system (Hg concentrations 0, 1.25, 2.5, 5 and 10 μmol/L) and from soil in pots and lysimeters (total Hg concentration (19.2 ± 1.9) mg/kg availability 0.07%, and (28.9 ± 0.4) mg/kg availability 0.09%, respectively), and investigated the accumulation and distribution of Hg in different parts of the plant. White lupin roots efficiently took up Hg, but its translocation to the harvestable parts of the plant was low. The Hg concentration in the seeds posed no risk to human health according to the recommendations of the World Health Organization, but the shoots should not be used as fodder for livestock, at least when unmixed with other fodder crops. The accumulation of Hg in the hydroponically-grown plants was linear over the concentration range tested. The amount of Hg retained in the roots, relative to the shoots, was almost constant irrespective of Hg dose (90%). In the soil experiments, Hg accumulation increased with exposure time and was the greater in the lysimeter than in the pot experiments. Although Hg removal was the greater in the hydroponic system, revealing the potential of the white lupin to extract Hg, bioaccumulation was the greatest in the lysimeter-grown plants; the latter system more likely reflects the true behaviour of white lupin in the field when Hg availability is a factor that limits Hg removal. The present results suggest that the white lupin could be used in long-term soil reclamation strategies that include the goal of profitable land use in Hg-polluted areas. 相似文献
829.
C.R. Rodríguez Pleguezuelo V.H. Durn Zuazo J.L. Muriel Fernndez F.J. Martín Peinado D. Franco Tarifa 《Agriculture, ecosystems & environment》2009,134(1-2):79-88
On the coast of Granada (SE, Spain), an economically important area for subtropical fruit cultivation, the crops are grown on orchard terraces. Also, high amounts of fertilizers, often excessive, are used in this type of intensive agriculture. However, each year significant fractions of nutrients taken up by the trees return to the soil by fallen leaves. Using a litter-bag technique, we assessed the decomposition rates and N-release in various types of litter. Our main purpose was to compare two different agroecosystem scenarios: (1) an unaltered slope consisting mainly of a mixture of herbaceous plants (Papaver rhoeas, Convolvulus sp., Malva sylvestris, Reseda phyteuma, Anacyclus sp., Sinapis arvensis, Medicago sp.) among spontaneous perennial woody shrubs (Genista umbellata, Olea europaea, Lavandula officinalis, Phlomis purpurea, Retama sphaerocarpa), and (2) an altered slope cultivated with subtropical trees on terraces: loquat (Eriobotrya japonica), mango (Mangifera indica), avocado (Persea americana), and cherimoya (Annona cherimola), with groundcover plantings of aromatic, medicinal, and melliferous plants (AMMPs) on the taluses of the terraces, which are usually used for erosion control: Lavandula dentata, Thymus mastichina, Satureja obovata, Rosmarinus officinalis, Anthyllis cytisoides. In the leaves from the subtropical crops, we found the highest decomposition rates in cherimoya and the lowest in mango (1.30 and 0.64 years−1, respectively). Leaves from mango and loquat registered initial peaks of N immobilization and later N-release, which was highest in cherimoya and avocado leaves (71.2 and 56.8% of the initial remaining N). In the spontaneous woody shrubs, O. europaea and G. umbellata were the slowest in decomposing (1.18 and 1.01 years−1, respectively) contrary to L. officinalis, which decomposed fastest (2.22 years−1). Only L. officinalis and P. purpurea registered a net N-release at the end of the study. The AMMPs showed different decomposition patterns: L. dentata registered the highest decomposition rates and Rosmarinus the lowest (1.9 and 1.1 years−1, respectively). T. mastichina, L. dentata, and S. obovata had the highest N-release, whereas R. officinalis and A. cytisoides showed N immobilization (183 and 122% of the initial N). Knowledge of the dynamics of nutrient release and litter decomposition will be useful for predicting nutrient availability and nutrient cycles in these types of agroecosystems where subtropical orchards are grown on terraces. 相似文献
830.
Organic farming is a whole-farm management approach believed to encourage biodiversity by excluding the input of agrochemicals and introducing specific management regimes for non-crop habitats. We examined the impact of the hedgerow management regime encouraged for organic farms on small mammal populations, since small mammal numbers influence a range of species at higher trophic levels and, in particular, are key to the conservation of a range of mammalian and avian predators. We compared differences in management and structure of non-crop habitats at the farm-scale between organic and conventional farms, and used within-farm variations in hedgerow size to predict the effect of hedgerow size on small mammals on both farm types. There were no significant differences in the proportion of non-crop habitats between organic and conventional farms, although management differences produced larger hedgerows on organic farms and greater diversity of hedgerow growth stages. However, a difference in hedgerow size between the farm types did not have a significant effect on small mammal abundance or diversity. We conclude that increased hedgerow size is not benefiting small mammal populations on organic farms: significant gains in small mammal numbers may be more effectively achieved by increasing the area of non-crop habitats rather than by improving management regimes. 相似文献