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1.
Interactions between zooplankton and fish in a fertilized lake 总被引:16,自引:0,他引:16
Arnfinn Langeland 《Ecography》1982,5(3):273-310
The effects of fish predation on the zooplankton community in an oligotrophic lake, Langvatn, near Trondheim in Central Norway, were investigated during a six-year period (1973–1978), together with the added effects of changes produced by adding artificial fertilizer in 1975 and 1976. The improved nutrient conditions in 1975 resulted in a rapid increase in biomass and production of the largest herbivore zooplankton species and of the fish population. A change in the behaviour and food habits of the arctic char was recorded; they became more pelagic and fed mainly on zooplankton. An increased survival rate of 0-group and biomass of planktivorous fish in 1975 enhanced the degree of fish predation on the zooplankton during subsequent years (1976–1978). As a consequence of fish predation, the composition of the zooplankton changed, from a mainly large-sized to a mainly small-sized community, dominated by Bosmina longirostris and rotifers. Since fish predation is size-selective and visibility-dependent, it induced a decrease in mean size and in body length at onset of maturity of the cladoceran populations and probably also weakened their ability to produce resting eggs. 相似文献
2.
Arnfinn Hykkerud Steindal Tran Thi Thu Tam Xiao Yun Lu Asta Juzeniene Johan Moan 《Photochemical & photobiological sciences》2008,7(7):814-818
5-Methyltetrahydrofolate (5MTHF) is the main form of folate in human plasma, and an important vitamin for human health. Photodegradation of folates may have played a role in the development of different human skin colours. 5MTHF can be degraded directly by exposure to ultraviolet radiation or by exposure to visible light in the presence of endogenous sensitizers like riboflavin (RF). These photochemical reactions were studied by absorption spectroscopy. While 5MTHF is stable under UV and visible light exposure in pure aqueous media, it is quickly degraded in the presence of RF during UVA and blue light exposure. The degradation of 5MTHF is dependent on the concentration of RF, but not on the concentration of 5MTHF itself. UVA and blue light gave similar reactions. Further investigations are necessary to evaluate the consequences of large light exposures in vivo in humans. Our findings should be taken into the ongoing discussion about the development of human skin colours. Due to the presence of RF in human blood, folate can be significantly degraded during prolonged or intense blue light exposure. Thus, a dark skin colour may be favourable for prevention of folate degradation under high solar fluence rates, such as in equatorial areas. 相似文献
3.
Cornel Pater Carl Ditlef Jacobsen Arnfinn Rollag Leiv Sandvik Jan Erikssen Else Karin Kogstad 《Trials》2000,1(3):177-7
Objectives
1. To assess the long-term effectiveness of a comprehensive cardiac rehabilitation programme on quality of life and survival in patients with a large spectrum of cardiovascular diseases (myocardial infarction, acute coronary syndrome, percutaneous transluminal coronary angioplasty and coronary artery bypass grafting). 2. To establish the degree of correlation between expected improvement of health-related quality of life and improvement in physical function attributable to rehabilitation in the intervention group, in comparison with similar changes in the conventional care group. 相似文献4.
Biomanipulation development in Norway 总被引:2,自引:2,他引:0
Since 1974 several studies have been carried out in Norway to investigate the interactions between planktivorous fish, zooplankton,
phytoplankton and water chemistry. Since 1978 a long-term national research program has been conducted by the Norwegian Council
for Scientific and Industrial Research (NTNF). In this program several whole lake manipulations of the fish stocks have been
performed to test hypotheses about trophic interactions. It was predicted that manipulations of planktivorous fish populations,
might also improve water quality in lakes undergoing eutrophication.
Two examples are given to illustrate the achieved results.
I: Whole lake fertilization experiment (1974–1978) carried out by Langeland and Reinertsen. The results revealed the importance
of top-down effects in the lake ecosystem. When cladocerans dominated, the zooplankton community was able to maintain a more
or less constant phytoplankton biomass and a rather low phytoplankton production even when nutrient levels were increased.
During years with rotifer dominance, algal biomass and productivity increased, despite the low amounts of added nutrients.
II: Experiment performed by Reinertsen, Jensen, Koksvik, Langeland and Olsen in the eutrophic Lake Haugatjern, total elimination
of the fish populations by rotenone in late 1980, resulted in a 4-fold decrease in the algal biomass. The species composition
changed from the dominance of large-sizedAnabaena flos-aquae andStaurastrum luetkemuelleri to smaller, fastgrowing species and gelatinous green algae.
The results are discussed in relation to management of inland waters by combined techniques of biomanipulation and reduced
external nutrient supply which increase food-chain efficiency. 相似文献
5.
Arnfinn Aulie Øivind Tøien 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1988,158(4):431-435
Summary Electromyographic activity (EMG) from the musculus pectoralis (breast muscle), m. iliotibialis (thigh muscle) and m. gastrocnemius (leg muscle), cloacal temperature (Tb) and O2 consumption were measured in bantam cocks (Gallus domesticus) exposed to different ambient temperatures (Ta). The same parameters were measured in bantam hens incubating eggs artificially thermoregulated to 40° and 25°C (Te).EMG activity appeared in thigh and leg muscles at Ta below 32°C (Tsh). This temperature probably represents the thermoneutral temperature (TNT) of the cock. EMG activity in breast muscles appeared at Ta below 20°C, or 4°C below the lower critical temperature (Tc).All muscles were quiet when the hen incubated 40°C egg at Ta=Tsh. When Te was abruptly changed to 25°C, EMG activity in the iliotibialis muscle appared 3 min before the activity in the pectoralis muscle. Tb dropped from 41.2° to 40.6°C in 14 min. When Te was returned to 40°C, the EMG activity in the pectoralis muscle disappeared almost at once, while the iliotibialis muscle was active until Tb returned to normal.Aerobic muscles seem to be responsible for shivering thermogenesis between Tc and Tsh, while anaerobic muscles are recruited at lower Ta or when the heat loss during incubation becomes severe.Abbreviations
EMG
electromyography
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Ta
ambient temperature
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Tb
cloacal temperature
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Tc
lower critical temperature
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Te
egg temperature
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TNT
thermoneutral temperature
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Tsh
shivering threshold temperature 相似文献
6.
Woldbaek PR Stromme TA Sande JB Christensen G Tønnessen T Ilebekk A 《American journal of physiology. Heart and circulatory physiology》2003,285(5):H2233-H2239
We have tested a new fiber-optic pressure recording system, Samba, with a thin fiber [outer diameter (OD) = 0.25 mm] and a pressure sensor (length and OD = 0.42 mm) attached to the end. The accuracy of the system tested in vitro was good, with a coefficient of variation of 2.54% at 100 mmHg. The drift was <0.45 mmHg/h, and the temperature sensitivity was approximately 0.07 mmHg/1 degrees C between 22 and 37 degrees C. The frequency response characteristics were similar to a 1.4-Fr Millar catheter (0-200 Hz). Introduction of the Samba sensor from the right carotid artery into the left ventricle in six mice caused no drop in mean aortic pressure, whereas introduction of a 1.4-Fr Millar catheter (OD = 0.47 mm; n = 6) caused a pressure drop from 91.6 +/- 9.2 to 65.1 +/- 6.2 mmHg; P < 0.05. Thus the Samba sensor system may represent a new alternative to assess hemodynamic variables in the murine cardiovascular system. 相似文献
7.
In the present study, we present for the first time the presence and distribution of neuropeptide Y (NPY) receptors Y1 and Y2 in the human postmortem heart using specific antibodies raised against extracellular parts of the receptors. A more intensive staining against the Y2 than against the Y1 receptors was detected on both atrial and ventricular cardiomyocytes. Immunoreactivity against both receptors was identified on both conducting fibers and cardiac nerves. More vessels stained positively for the Y2 than for the Y1 receptor, but the Y1 receptors were more abundant in subendocardial than subepicardial vessels of the left ventricular wall. 相似文献
8.
Jon Elling Pettersen Gunnar Arnfinn Ulsaker Egil Jellum 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1978,145(3)
2,4′-Isobutylphenylpropionic acid (ibuprofen) has previously been demonstrated to yield four urinary metabolites, formed by ω1-, ω2- and ω3-hydroxylation and by a further oxidation of the primary alcohol of the ω1-hydroxylated metabolite to a carboxyl group. By synthesis and gas chromatography—mass spectrometry the suggested structure of the ω3-hydroxylated metabolite was verified in the present study. Moreover, a new metabolite, 2,4′-carboxyphenylpropionic acid, was demonstrated to be present in substantial amounts in dialysis fluid from a nephrectomized patient. In such patients ingested drugs cannot be excreted in the urine, but are metabolized to end products. Thus, dialysis fluid may be a convenient medium for studies on drug metabolism. 相似文献
9.
Iren H?yland L?hr Nils Hülter Eva Bernhoff P?l Jarle Johnsen Arnfinn Sundsfjord Umaer Naseer 《PloS one》2015,10(3)
Objectives
To characterize the CTX-M-15-encoding plasmid in a Klebsiella pneumoniae ST17 strain, responsible for an outbreak at a Norwegian neonatal intensive care unit and subsequent colonization of affected children for up to two years. To identify plasmid-mediated features relevant for the outbreak dynamics, and to investigate the plasmids capability of horizontal transfer, its segregational stability and plasmid-mediated fitness costs.Methods
Plasmid profiling was performed by S1-nuclease PFGE, PCR-based replicon typing and Southern blot-hybridization. The complete sequence of the CTX-M-15-encoding plasmid was obtained by 454 sequencing. Plasmid self-transferability was investigated by broth- and filter mating, segregational stability was explored by serial passage, and plasmid-conferred fitness costs were examined in pairwise head-to-head competitions and by growth rate comparisons.Results
CTX-M-15 was encoded by a ~180 kb IncFIIK plasmid in K. pneumoniae ST17. S1-nuclease PFGE profiles of the first and the last CTX-M-15-producing K. pneumoniae isolates, recovered from the four children colonized the longest, suggested that the plasmid was stably maintained during intestinal carriage of up to two years. The DNA sequence of the pKPN3-like plasmid, pKp848CTX, uncovered a Tn3-like antibiotic resistance region and multiple heavy metal- and thermoresistance determinants. Plasmid pKp848CTX could not be transferred to Escherichia coli in vitro and we found no evidence to support horizontal plasmid transfer in vivo. Segregational plasmid loss ranging from 0.83% to 17.5% was demonstrated in evolved populations in vitro, but only minor fitness costs were associated with plasmid-carriage.Conclusions
Plasmid pKp848CTX encodes phenotypic traits, which may have had an impact on the fitness and survival of the K. pneumoniae ST17 strain in the outbreak setting. The antibiotic resistance plasmid pKp848CTX was stably maintained during two years of intestinal colonization, conferring negligible fitness cost to its host, and thus seem well adapted to its K. pneumoniae host. 相似文献10.
St?le Tofteland Umaer Naseer Jan Helge Lislevand Arnfinn Sundsfjord ?rjan Samuelsen 《PloS one》2013,8(3)