562 resultados para Migrations


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Members of the calcareous nannofossil genus Discoaster have been used extensively to subdivide Tertiary deep-sea sediments into biostratigraphic zones or subzones (e.g., Martini, 1971; Bukry, 1973). Haq and Lohmann (1976) mapped biogeographic migrations of this group through time and over latitude. They suggested that expansions and contractions of Discoaster-dominated assemblages across latitudes reflect sea-surface temperature changes. Subsequently, late Pliocene Discoaster species were counted at closely spaced sample intervals from various Atlantic sites (Backman et al., 1986; Backman and Pestiaux, 1987; Chepstow-Lusty et al., 1989, 1991), and Indian Ocean as well as Pacific Ocean sites (Chepstow-Lusty, 1990). In addition to the biostratigraphic information revealing positions and the precision by which the different late Pliocene Discoaster species can be determined, these studies also demonstrated that discoasters strongly fluctuate in abundance as a function of time. These abundance variations occur in equatorial as well as temperate temperature regimes, and show periodicities that reflect orbital frequencies. Chepstow-Lusty et al. (1989, 1991) also suggested that the oscillating abundances partly represent productivity pressure, because discoasters tend to show low abundances under high productivity conditions and vice versa. In the Pacific Ocean, counts showing late Pliocene Discoaster abundances exist from three sites, namely Ocean Drilling Program (ODP) Site 677 in the eastern equatorial upwelling region, Core V28-179 from the central equatorial region, and Core V32-127 from the mid-latitude Hess Rise. The two Vema cores are condensed and show sedimentation rates below 0.5 cm/1000 yr, thus offering a poorly resolved stratigraphy. Hole 806C from the Ontong Java Plateau provided an opportunity to establish a highly resolved Discoaster record from the western extreme of the equatorial Pacific under an environmental setting that differed from ODP Site 677 by being less influenced by intense upwelling. The Discoaster counting technique is described by Backman and Shackleton (1983).

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A total of 51,074 archaeological sites from the early Neolithic to the early Iron Age (c. 8000-500 BC), with a spatial extent covering most regions of China (c. 73-131°E and c. 20-53°N), were analysed over space and time in this study. Site maps of 25 Chinese provinces, autonomous regions and municipalities, published in the series 'Atlas of Chinese Cultural Relics', were used to extract, digitalise and correlate its archaeological data. The data were, in turn, entered into a database using a self-developed mapping software that makes the data, in a dynamic way, analysable as a contribution to various scientific questions, such as population growth and migrations, spread of agriculture and changes in subsistence strategies. The results clearly show asynchronous patterns of changes between the northern and southern parts of China (i.e. north and south of the Yangtze River, respectively) but also within these macro-regions. In the northern part of China (i.e. along the Yellow River and its tributaries and in the Xiliao River basin), the first noticeable increase in the concentration of Neolithic sites occurred between c. 5000 and 4000 BC; however, highest site concentrations were reached between c. 2000 and 500 BC. Our analysis shows a radical north-eastern shift of high site-density clusters (over 50 sites per 100 * 100 km grid cell) from the Wei and middle/lower Yellow Rivers to the Liao River system sometime between 2350 BC and 1750 BC. This shift is hypothetically discussed in the context of the incorporation of West Asian domesticated animals and plants into the existing northern Chinese agricultural system. In the southern part of China, archaeological sites do not show a noticeable increase in the absolute number of sites until after c. 1500 BC, reaching a maximum around 1000 BC.

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Mode of access: Internet.

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I. bd. Vorwort zur neuen auflage. Einleitung der neuen auflage. 1. buch. Die Germanen vor der völkerwanderung bis zu dem abzug der Gothen an die Donau und dem Markomannenkrieg. 2. buch. Die zeit vom auftreten der Gothen an der Donau und dem Markomannenkrieg bis zum Hunnen-einfall. Anhang zum I. band: A. Anmerkungen. B. Excurse.--II. bd. 3. buch. Von dem Hunnen-einfall bis zu den letzten bewegungen der völkerwanderung (375-568) Anhang zum II. band: A. Anmerkungen. B. Excurse. Berichtigungen und druckfehler. Alphabetisches sachregister. Quellen-und literatur-uebersicht (von F. Dahn)

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The "Register mit vier Karten und einer Stammtafel" forms a separate volume with cover-title.

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Programm- Landes-ober-realschule, Kremsier.

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Mode of access: Internet.

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Theil 2 has special t. p. with imprint: Weimar, H. Böhlau.

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"In this monograph we are to subject to intimate examination the discovery record of one new-found language ... Sissano."--p. 3.

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Two water quality monitoring strategies designed to sample hydrophobic organic contaminants have been applied and evaluated across an expected concentration gradient in PAHs in the Moreton region. Semipermeable membrane devices (SPMDs) that sequester contaminants via passive diffusion across a membrane were used to evaluate the concentration of PAHs at four and five sites in spring and summer 2001/2002, respectively. In addition, induction of hepatic cytochrome P4501, EROD activity, in yellowfin bream, Acanthopagrus australis, captured in the vicinity of SPMD sampling sites following deployment in summer was used as a biomarker of exposure to PAHs and related chemicals. SPMDs identified a clear and reproducible gradient in PAH contamination with levels increasing from east to west in Moreton Bay and upstream in the Brisbane River. The highest PAH concentrations expressed as B(a)P-toxicity equivalents (TEQs) were found in urban areas, which were also furthest upstream and experienced the least flushing. Cytochrome P4501 induction in A. australis was similar at all sites. The absence of clear trends in EROD activity may be attributable to factors not measured in this study or variable residency time of A. australis in contaminated areas. It is also possible that fish in the Moreton region are displaying enzymatic adaptation, which has been reported previously for fish subjected to chronic exposure to organic contaminants. These potential interferences complicate interpretation of EROD activity from feral biota. It is, therefore, suggested that future monitoring combine the two methods by applying passive sampler extracts to in vitro EROD assays. (C) 2004 Elsevier Ltd. All rights reserved.

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Both large and small scale migrations of Helicoverpa armigera Hübner in Australia were investigated using AMOVA analysis and genetic assignment tests. Five microsatellite loci were screened across 3142 individuals from 16 localities in eight major cotton and grain growing regions within Australia, over a 38-month period (November 1999 to January 2003). From November 1999 to March 2001 relatively low levels of migration were characterized between growing regions. Substantially higher than average gene-flow rates and limited differentiation between cropping regions characterized the period from April 2001 to March 2002. A reduced migration rate in the year from April 2002 to March 2003 resulted in significant genetic structuring between cropping regions. This differentiation was established within two or three generations. Genetic drift alone is unlikely to drive genetic differentiation over such a small number of generations, unless it is accompanied by extreme bottlenecks and/or selection. Helicoverpa armigera in Australia demonstrated isolation by distance, so immigration into cropping regions is more likely to come from nearby regions than from afar. This effect was most pronounced in years with limited migration. However, there is evidence of long distance dispersal events in periods of high migration (April 2001-March 2002). The implications of highly variable migration patterns for resistance management are considered.

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Many long-lived marine species exhibit life history traits. that make them more vulnerable to overexploitation. Accurate population trend analysis is essential for development and assessment of management plans for these species. However, because many of these species disperse over large geographic areas, have life stages inaccessible to human surveyors, and/or undergo complex developmental migrations, data on trends in abundance are often available for only one stage of the population, usually breeding adults. The green turtle (Chelonia mydas) is one of these long-lived species for which population trends are based almost exclusively on either numbers of females that emerge to nest or numbers of nests deposited each year on geographically restricted beaches. In this study, we generated estimates of annual abundance for juvenile green turtles at two foraging grounds in the Bahamas based on long-term capture-mark-recapture (CMR) studies at Union Creek (24 years) and Conception Creek (13 years), using a two-stage approach. First, we estimated recapture probabilities from CMR data using the Cormack-Jolly-Seber models in the software program MARK; second, we estimated annual abundance of green turtles. at both study sites using the recapture probabilities in a Horvitz-Thompson type estimation procedure. Green turtle abundance did not change significantly in Conception Creek, but, in Union Creek, green turtle abundance had successive phases of significant increase, significant decrease, and stability. These changes in abundance resulted from changes in immigration, not survival or emigration. The trends in abundance on the foraging grounds did not conform to the significantly increasing trend for the major nesting population at Tortuguero, Costa Rica. This disparity highlights the challenges of assessing population-wide trends of green turtles and other long-lived species. The best approach for monitoring population trends may be a combination of (1) extensive surveys to provide data for large-scale trends in relative population abundance, and (2) intensive surveys, using CMR techniques, to estimate absolute abundance and evaluate the demographic processes' driving the trends.