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排序方式: 共有204条查询结果,搜索用时 62 毫秒
191.
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The Science of Nature - 相似文献
194.
Erich v. Drygalski A. Heintz G. Melchers W. Schnakenbeck 《Die Naturwissenschaften》1938,26(15):236-238
195.
Anja Gladbach David Joachim Gladbach Martina Koch Alexandra Kuchar Erich Möstl Petra Quillfeldt 《Behavioral ecology and sociobiology》2011,65(7):1491-1498
The measurement of faecal glucocorticoid metabolites is used as a non-invasive technique to study stress in animal populations.
They have been used most widely in mammals, and mammalian studies have also treated issues such as sample stability and storage
methods. In birds, faecal corticosterone metabolite (CM) assays have been validated for a small number of species, and adequate
storage under field conditions has not been addressed explicitly in previous studies. Furthermore, while it is well-established
that baseline plasma corticosterone levels in birds rise with declining body condition, no study so far investigated if this
relationship is also reflected in faecal samples. We here present data of a field study in wild Upland geese Chloephaga picta leucoptera on the Falkland Islands, testing different storage methods and investigating the relationship of faecal CM concentrations
to body condition and reproductive parameters. We found that faecal CM measures are significantly repeatable within individuals,
higher in individuals with lower body condition in both male and female wild Upland geese and higher in later breeding females
with smaller broods. These results suggest that measuring faecal CM values may be a valuable non-invasive tool to monitor
the relative condition or health of individuals and populations, especially in areas where there still is intense hunting
practice. 相似文献
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Julia Wohlers-Z?llner Antje Biermann Anja Engel Petra D?rge Aleksandra M. Lewandowska Markus von Scheibner Ulf Riebesell 《Marine Biology》2012,159(11):2503-2518
A comparative analysis of data, obtained during four indoor-mesocosm experiments with natural spring plankton communities from the Baltic Sea, was conducted to investigate whether biogeochemical cycling is affected by an increase in water temperature of up to 6?°C above present-day conditions. In all experiments, warming stimulated in particular heterotrophic bacterial processes and had an accelerating effect on the temporal development of phytoplankton blooms. This was also mirrored in the build-up and partitioning of organic matter between particulate and dissolved phases. Thus, warming increased both the magnitude and rate of dissolved organic carbon (DOC) build-up, whereas the accumulation of particulate organic carbon (POC) and phosphorus (POP) decreased with rising temperature. In concert, the observed temperature-mediated changes in biogeochemical components suggest strong shifts in the functioning of marine pelagic food webs and the ocean’s biological carbon pump, hence providing potential feedback mechanisms to Earth’s climate system. 相似文献
198.
Frederick W. Kutz Donald G. Barnes Erich W. Bretthauer David P. Bottimore Helmut Greim 《毒物与环境化学》2013,95(1-4):99-109
The International Toxicity Equivalency Factor (I‐TEF) method of risk assessment is a revised interim procedure for assessing the risks associated with exposures to complex mixtures of chlorinated dibenzo‐p‐dioxins and dibenzofurans (CDDs and CDFs). This updated scheme was developed by a working group of the North Atlantic Treaty Organization's Committee on the Challenges of Modern Society and has been officially adopted by the U.S. Environmental Protection Agency (EPA), Canada, Ontario Ministry of the Environment, the Nordic countries, the Netherlands, and the United Kingdom. Prior to the development of the I‐TEF method, at least ten slightly different schemes had been used throughout the world which complicated communication among scientists and regulatory agencies concerning the toxicological significance of complex mixtures of CDDs and CDFs. The I‐TEF approach facilitates risk communication internationally by reducing large volumes of analytical data into a single number‐International Toxicity Equivalents (I‐TEQ). As a result, the I‐TEF method represents an improvement in an already useful risk assessment/regulatory tool. 相似文献
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Summary. Summary. Oilseed rape, Brassica napus L. (cv Express),
plants were grown under three different sulphur regimes:
sulphur-free (S0), normal sulphur (Sn, normal field concentration)
and a sulphur-rich (S+, 2 × concentration of Sn). We
performed dual choice oviposition assays with the diamondback
moth, Plutella xylostella, using real plants and,
for the first time with this insect, artificial leaves sprayed
with methanolic leaf-surface extracts. The results mirrored
those of a separate study of preferences for whole plants.
Females laid more eggs on surrogate leaves that were
treated with Sn extracts than on S0 plants, while only a
slight, not significant, difference was observed between
extracts of normal and sulphur-rich plants. This shows
that chemical compounds on the leaf surface mediate the
oviposition preference and that the female insect can
perceive the quality of the host-plants in terms of their
fertilisation status.Since leaf volatiles are known to be oviposition stimulants,
we investigated the effects of leaf-surface extracts on
insect olfactory responses using electroantennograms
(EAGs). In agreement with the behavioural data, we found
that extracts of sulphur-treated plants yielded higher EAG
amplitudes than the S0 extracts. Since the leaf content of the
volatiles isothiocyanates is influenced by sulphur nutrition,
we analysed the extracts for these compounds. Above the
detection threshold of our GC-MS system, no isothiocyanates
were found. Thus, other compounds present in the
surface extracts must be perceived by the antenna.However, the HPLC analysis revealed 11 different
glucosinolates. Progoitrin (2-Hydroxy-3-butenyl) and
gluconapoleiferin (2-Hydroxy-4-pentenyl), which belong to
the hydroxy-alkene class of glucosinolates, were the most
abundant compounds. The total glucosinolate content
sharply increased from S0 to Sn plants, whereas it was slightly
lower in n versus S+ plants. Since it is known that glucosinolates
can stimulate oviposition, it seems likely that the
increased content we observed was influencing the insect
preference in this study too. 相似文献