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51.
Michael Schaub 《Journal of Ornithology》1996,137(2):213-227
Zusammenfassung In der Brutsaison 1994 wurde das Jagdverhalten von fünf Rotkopfwürgerpaaren in der Nordschweiz beobachtet, das Nahrungsangebot mit der Sichtkreismethode erfaßt. Bei warmem und trockenem Wetter waren die Insekten aktiver und somit das Nahrungsangebot für die Rotkopfwürger günstiger. In hoher Vegetation gab es mehr Insekten als in niedriger. Die Rotkopfwürger jagten entweder am Boden (64% der Jagdflüge) oder in der Luft (36%). Die Bodenjagden waren energetisch günstiger, da die Beute durchschnittlich größer und die Jagddistanz kleiner war. Bodenjagden fanden vorzugsweise in Flächen mit kurzer Vegetation (durchschnittliche Vegetationshöhe: 7 cm) statt. Gejagt wurden ausschließlich Arthropoden und zwar gezielt große. Bei schlechten Wetterbedingungen mußten auch kleinere Beutetiere gefangen werden. Der Fluganteil am Gesamtzeitbudget war während der Nestlingszeit am größten. Zur Bebrütungs- und Nestlingszeit wurden die Jagdaktivitäten bei schlechtem Wetter gegenüber gutem tendenziell gesteigert, vor dem Brüten und nach dem Flüggewerden der Jungen aber eher gesenkt. Der Fluganteil beim Jagen über kurzer Vegetation schien kleiner als beim Jagen über hoher Vegetation.
Hunting behavior and time budget of Woodchat ShrikesLanius senator in Northern Switzerland
The hunting behavior of Woodchat Shrike in Northern Switzerland was studied by visual observations of five pairs in 1994. Data on food supply were collected by standardized observations in half-circles of 1 m radius. During warm and dry weather the activity of the insects increased. More insects were seen in high than in short vegetation. The Woodchat Shrikes either hunted on the ground (64% of all hunting flights) or in the air (36%). The energy gain in ground-huntings was higher than in flycatching due to larger average prey size and a shorter hunting distance. Ground huntings occured mainly in areas with short vegetation (7 cm high on average). The birds only fed on arthropods, preferring larger seizes. During bad weather they were dependant also on smaller prey. The proportion of time the adults spent in flight was longest during the nestling season. In bad weather, hunting activity was slightly increased during incubation and nestling stage but low before incubation and after fledging of the young. For hunting over short vegetation the birds seemed to spent less time in flight than for hunting over high vegetation.相似文献
52.
Actions of Rho family small G proteins and p21-activated protein kinases on mitogen-activated protein kinase family members. 总被引:22,自引:7,他引:15
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The mitogen-activated protein (MAP) kinases are a family of serine/threonine kinases that are regulated by distinct extracellular stimuli. The currently known members include extracellular signal-regulated protein kinase 1 (ERK1), ERK2, the c-Jun N-terminal kinase/stress-activated protein kinases (JNK/SAPKs), and p38 MAP kinases. We find that overexpression of the Ste20-related enzymes p21-activated kinase 1 (PAK1) and PAK2 in 293 cells is sufficient to activate JNK/SAPK and to a lesser extent p38 MAP kinase but not ERK2. Rat MAP/ERK kinase kinase 1 can stimulate the activity of each of these MAP kinases. Although neither activated Rac nor the PAKs stimulate ERK2 activity, overexpression of either dominant negative Rac2 or the N-terminal regulatory domain of PAK1 inhibits Ras-mediated activation of ERK2, suggesting a permissive role for Rac in the control of the ERK pathway. Furthermore, constitutively active Rac2, Cdc42hs, and RhoA synergize with an activated form of Raf to increase ERK2 activity. These findings reveal a previously unrecognized connection between Rho family small G proteins and the ERK pathway. 相似文献
53.
Concerted action of RAS and G proteins in the sexual response pathways of Schizosaccharomyces pombe. 总被引:9,自引:4,他引:5
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We have shown that the expression of mam2, the gene encoding the Schizosaccharomyces pombe P-factor pheromone receptor, is dependent upon components of the pheromone signal transduction pathway, including Ras1, Gpa1, Byr1 and Byr2, each of which is required for both conjugation and sporulation. Studies of the expression of mam2 in mutant S. pombe cells confirm previous conclusions, based on the ability of cells to sporulate, that the Byr1 protein kinase acts downstream of the Byr2 protein kinase and that both act downstream of Ras1, the S. pombe RAS homolog, and Gpa1, the G alpha component that mediates the occupancy of the mam2 receptor. In addition, our present studies show that Ras1 and Gpa1 each act downstream from the other and hence act in concert. The Spk1 kinase, which is required for conjugation and sporulation and which is a structural and functional homolog of the vertebrate MAP kinases, is not required for mam2 expression. 相似文献
54.
The uptake of lead by two contrasting plant species, radish and red fescue, grown in soils contaminated by mine spoil was investigated. Uptake was found to be poorly correlated either with pH or total Pb concentration in the soils. By contrast, a good correlation was obtained, particularly for red fescue, between Pb uptake and Pb concentration in the solution of equilibrated soil suspensions over a wide range of soil pH, total soil Pb and soil solution Pb concentration.Calculations suggested a similar order of magnitude in the total amounts of Pb taken up by the plants and Pb in the soil solution of the root zone, justifying the latter as a good index of Pb-availability. ei]Section editor: A C Borstlap 相似文献
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A new selectively neutral mutation occurs in a multilocus genetic background that has achieved a stable equilibrium at which there is a linkage disequilibrium. Perturbation techniques are applied to an extension of the branching process formulation of Fisher in order to address the question of extinction probabilities. We show that under appropriate conditions the probability of extinction of the new mutant is increased by the existence of linkage disequilibrium in the genetic background.Research supported in part by NIH grant GM 28016 相似文献
60.
Root Morphology and Nitrogen Uptake of Maize Simultaneously Supplied with Ammonium and Nitrate in a Split-root System 总被引:11,自引:0,他引:11
We studied the response of maize (Zea mays L. cv. Anjou 256)to a simultaneous, but separated supply of ammonium and nitrate(localized supply, LS). A split-root system was used to supplyhalf of the roots with ammonium and the other half with nitrate.A homogeneously distributed supply of both nitrogen forms (HS)was the control treatment. Seedlings were grown for 12 d fromthe two-leaf to the three-leaf stage in hydroponics at threepH levels (4, 5·5 and 7). The total N concentration was3 mol m-3. The split-root system was established by removingthe seminal root system and using only four nodal roots perplant. Total root length and root surface area were recordedautomatically with a modified Delta- T area meter. Other morphologicalroot traits (such as main axis length and diameter, number,density, and length of laterals) were recorded manually. Uptakeof ammonium and nitrate was measured by the depletion of thenutrient solution. As compared with LS, HS was superior in shootand root DM, total root length and root surface area, ammoniumand nitrate uptake and shoot nitrogen concentration, irrespectiveof pH level. This indicates that, also under field conditions,mixed ammonium and nitrate fertilization is only beneficialto plant growth if both N forms are evenly distributed in thesoil. At both HS and LS, ascending pH increased the ammonium:nitrateuptake ratio. At LS, declining pH induced a considerable shiftin the distribution of root DM, root length, and root surfacearea the nitrate-fed compartment.Copyright 1993, 1999 AcademicPress Maize, Zea may L., ammonium, nitrate, pH, root morphology, split-root 相似文献