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361.
362.
This article explains the position(s) of the United States in the maritime dispute adjacent to Svalbard. While the United States has regarded Norway's exclusive claim to the natural resources outside Svalbard as everything from “wishful thinking” to legally plausible, Washington maintains that it may have rights under the 1920 Svalbard Treaty to exploit the maritime zones adjacent to the archipelago. The U.S. reservation is the result of assessments and reassessments of legal considerations as well as national interests.  相似文献   
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364.
In a search for slowly evolving nuclear genes that may cast light on the deep evolution of plants, we carried out phylogenetic analyses of two well-characterized subfamilies of P-type pumps (P2A and P5A ATPases) from representative branches of the eukaryotic tree of life. Both P-type ATPase genes were duplicated very early in eukaryotic evolution and before the divergence of the present eukaryotic supergroups. Synapomorphies identified in the sequences provide evidence that green plants and red algae are more distantly related than are green plants and eukaryotic supergroups in which secondary or tertiary plastids are common, such as several groups belonging to the clade that includes Stramenopiles, Alveolata, Rhizaria, Cryptophyta and Haptophyta (SAR). We propose that red algae branched off soon after the first photosynthesizing eukaryote had acquired a primary plastid, while in another lineage that led to SAR, the primary plastid was lost but, in some cases, regained as a secondary or tertiary plastid.  相似文献   
365.
Evolutionary theory predicts that in metapopulations subject to rapid extinction–recolonization dynamics, natural selection should favour evolution of traits that enhance dispersal and recolonization ability. Metapopulations of field voles (Microtus agrestis) on islands in the Stockholm archipelago, Sweden, are characterized by frequent local extinction and recolonization of subpopulations. Here, we show that voles on the islands were larger and had longer feet than expected for their body size, compared with voles from the mainland; that body size and size-specific foot length increased with increasing geographical isolation and distance from mainland; and that the differences in body size and size-specific foot length were genetically based. These findings provide rare evidence for relatively recent (less than 1000 years) and rapid (corresponding to 100–250 darwins) evolution of traits facilitating dispersal and recolonization in island metapopulations.  相似文献   
366.

Based mainly on pollen influx data, an attempt is made at reconstructing Holocene tree‐line fluctuations and palaeotemperatures in central Troms, North Norway. Both past and present‐day (Tauber trap) pollen influx data suggest that influx rates exceeding 250–300 pollen/cm2/year for each of the major arboreal taxa (Betula pubescens and Pinus sylvestris) are only found at sites with corresponding forest types in the immediate surroundings. High influx rates, raised tree‐lines and favourable climatic periods are recorded at 7500–4500 and 3000–2600 B.P. Betula and Pinus woodlands may have reached more than 200 m above their present altitude limits, suggesting a July mean temperature 2°C higher than at present during the Holocene optimum.  相似文献   
367.
The Hieracium flora of westernmost Dalarna, comprising the southern fringe of the Scandes alps (central Scandinavia), is extremely rich in species. The area is dominated by species-poor coniferous sub-alpine and taiga forest, but within this matrix there are small and isolated sites with high species richness of both Hieracium and other plants. Both steep mountain slopes with outcrops of base-rich bedrock and moving ground water, and old seasonal or permanant human settlements constitute such biodiversity hotspots. However, today the former are threatened by modern forestry practices and/or exploitation for winter tourism and the latter are commonly abandoned and subjected to severe overgrowth or dramatically changed land-use. The area was thorougly surveyed in 1897–1921. In 2007, the same region and partly the same sites, were revisited. In 1897–1921, 15 Hieracium species were on average recorded from each site, but when the same sites were revisited in 2007 significantly fewer, only about 6 (40%) species per site, were refound. As far as the total species pool of the study area is concerned, it consisted of 168 species in 1897–1921, whereof only 117 (67%) were found in 2007. This remarkable reduction in species richness at both the local and the regional scale is attributable to both modern forestry practices and to the cessation of traditional agricultural practices like hay-making on semi-natural grasslands and extensive cattle-grazing in the forests. It is concluded that to reduce the on-going severe loss of biodiversity in the sub-alpine and taiga regions, conservation efforts in these areas ought to be enhanced and concentrated not only on saving what still remains of old-growth forest but also on managing remnants of grasslands and formerly grazed or mowed open forests around former settlements.  相似文献   
368.
Sami reindeer herders in northern Fennoscandia have historically cut trees with high quantities of arboreal lichens to feed their animals during harsh winters. In this study we analysed temporal and spatial patterns of lichen-tree cuttings of Scots pine in a remote forest landscape in northern Sweden. We wanted to test the hypothesis that repeated cutting of such trees may have had long-lasting effects on the forest ecosystem that are still discernable today. Our analyses included an inventory of remaining lichen-tree stumps, and a field survey of forest variables to relate structural variation within the forest to these cuttings. We used dendrochronological methods to date stumps and reconstruct forest structure. Our results show that more than 7,000 trees were cut for this purpose over a period of almost 300 years within an area covering 6 km2. Lichen-tree cutting was most intense during the late 18th century when ca. 600–1,000 trees were cut during each decade. We did not detect any significant relationship between past lichen-tree cutting and present small-scale forest heterogeneity, and suggest that this might be due to the small size of the cut trees and the long time elapsed since most of the cuttings. We conclude that vestiges such as stumps from lichen-tree cutting are highly valuable for our understanding of past land use. Furthermore, since they are located in an unlogged and very old forest, this highlights the need to acknowledge the interconnectedness between ecological and cultural values of such forests and the need to identify and protect them.  相似文献   
369.
LC–MS based global metabolite profiling currently lacks detailed guidelines to demonstrate that the obtained data is of high enough analytical quality. Insufficient data quality may result in the failure to generate a hypothesis, or in the worst case, a false or skewed hypothesis. After assessing the literature, it is apparent that an analytically focused summary and critical discussion related to this subject would be beneficial for both beginners and experts engaged in this field. A particular focus will be placed on data quality, which we here define as the degree to which a set of parameters fulfills predetermined criteria, similar to the established guidelines for targeted analysis. However, several of these parameters are difficult to assess since holistic approaches measure thousands of metabolites in parallel and seldom include predefined knowledge of which metabolites will differ between sample groups. In this review, the following parameters will be discussed in detail: reproducibility, selectivity, certainty of metabolite identification and metabolite coverage. The review systematically describes the generic workflow for LC–MS based global metabolite profiling and highlights how each separate part may affect data quality. The last part of the review describes how data quality can be evaluated as well as identifies areas where additional improvement is needed. In this review, we provide our own analytical opinions in regards to evaluation and, to some extent, improvement of data quality.  相似文献   
370.
Does seed dormancy benefit the mother plant by reducing sib competition?   总被引:1,自引:0,他引:1  
Summary Seed dormancy has been considered, almost without exception, as a bet-hedging strategy in a temporally varying environment. However, in this paper we show that seed dormancy can improve the reproductive success of the mother plant when competition between sibling seedlings and adult plants is intense even if the environment is temporally invariable. We allow a cohort of sibling seeds to germinate simultaneously in the same patch and assume a density dependent survival and fecundity of seedlings. In the model, the mother plant is assumed to control the germination behaviour of the seeds, e.g. by enclosing the seeds in coats of different hardiness. When sib competition is intense, a postponed germination of her seeds can increase the reproductive success of the mother plant up to four times, measured in terms of the number of grandchildren. Consequently, our results suggest that postponed germination may function as a mechanism that alters local interactions in viscous plant populations with limited dispersal.  相似文献   
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