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1.
There is a growing interest in understanding the influence of plant traits on their ability to spread in non-native regions. Many studies addressing this issue have been based on relatively small areas or restricted taxonomic groups. Here, we analyse a large data base involving 1567 plant species introduced between Eastern Asia and North America or from elsewhere to both regions. We related the extent of species distributions in each region to growth form and the distinction between upland and wetland habitats. We identified significant relationships between geographical distribution and plant traits in both native and exotic ranges as well as regional differences in the relationships. Range size was larger for herbaceous graminoids and forbs, especially annuals compared to perennials, than for woody species, and range size also was larger for plants of wetland compared to upland habitats. Distributions were more extensive in North America than in Eastern Asia, although native plants from both regions had broader distributions than non-natives, with exotics from elsewhere intermediate. Growth form and environment explained more of the variance in distribution of plants in North America than in Eastern Asia. The influence of growth form and habitat on distribution suggests that these traits might be related to tolerance of ecological conditions. In addition, the smaller extents of species in non-native compared to native areas suggest roles for dispersal limitation and adaptation to region-specific ecological conditions in determining distribution.  相似文献   
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《Ethnic and racial studies》2012,35(8):1447-1465
Abstract

Data on race have been collected in South African censuses for a century. We examine the role played by the census in solidifying race as a social statistic and show that, in contrast to the majority of situations, operational and legislative factors rendered the census largely unimportant as a vehicle for doing this. Since 1994, race has been entirely self-reported and not subject to state reinterpretation. We examine the implications of this for future data collection exercises and caution against reifying race as a predictor of social outcomes in post-apartheid South Africa, and argue for its gradual phasing out.  相似文献   
4.
《Ethnic and racial studies》2012,35(6):988-1006
Abstract

This article examines how South Asian American communities ascribe meaning to the category of ‘race’ while adding their own sensibilities to racial categories of ‘black’ and ‘white’. Drawing upon ethnographic methods, I analyse leisure spaces of basketball to demonstrate how racial formation in the US for non-white ethnic American subjects engages the black–white racial binary while simultaneously critiquing this racial logic. Racial categories provide a lexicon for comprehending South Asian American difference, while South Asian idioms perpetuate racializing discourses.  相似文献   
5.
A new genus, Meishanorhynchia , is proposed based on new material from the Lower Triassic of the Meishan section, South China. It is of a late Griesbachian age based on both associated biozones (ammonoids and bivalves) and radiometric dates of the intercalated volcanic ash beds. Comparison with both Palaeozoic and Mesozoic–Cenozoic-related genera suggests that it may represent the first radiation of progenitor brachiopods in the aftermath of the end-Permian extinction. The lowest brachiopod horizon that contains the genus is estimated to be about 250.1 ± 0.3 Ma. This implies that the initial stage of recovery of Brachiopoda in the Early Triassic was probably about 1.3 ± 0.3 myr after the major pulse of the end-Permian mass extinction (dated as 251.4 ± 0.3 Ma). This is in agreement with Hallam's expectancy that biotic recovery typically begins within one million years or so of major mass extinctions, in contrast to current views on the end-Permian extinction event which propose that the recovery of most if not all biotic groups in the Early Triassic was severely delayed and only began about five million years after the end-Permian extinction.  相似文献   
6.
南海南沙海域沉积物中可培养微生物及其多样性分析   总被引:10,自引:0,他引:10  
【目的】为了从南沙海域中分离获得微生物菌种资源,【方法】本文通过沉积物采样、可培养菌分离及16S rRNA鉴定,【结果】从22个站点的沉积物样品中获得349株细菌,分属于87个种。发现产芽孢细菌分布最广,并在10个站点的分离株中占多数;它们是Bacillus,Halobacillus,Brevibacillus,Paenibacillus,Pontibacillus和Thalassobacillus。其中芽孢杆菌(Bacillus)无论在数量上还是种类上都最多,分别属于34种,其中有8个可能的新种。此外,g-Proteobacteria是分离率较高的另一亚群;其中,假单胞菌(Pseudomonas),海杆菌(Marinobacter),食烷菌(Alcanivorax)属的细菌最多。统计还发现,在深度750~2000 m之间,低GC含量的细菌最丰富,而深度2000 m以下,分离株则全部为g-Proteobacteria。【结论】南沙沉积物可培养微生物中产芽孢细菌及 g-Proteobacteria比较丰富;其中,产芽孢细菌的多样性最高,具有进一步研究开发价值。  相似文献   
7.
ABSTRACT Delineating populations is critical for understanding population dynamics and managing habitats. Our objective was to delineate subpopulations of migratory female white-tailed deer (Odocoileus virginianus) in the central Black Hills, South Dakota and Wyoming, USA, on summer and winter ranges. We used fuzzy classification to assign radiocollared deer to subpopulations based on spatial location, characterized subpopulations by trapping sites, and explored relationships among survival of subpopulations and habitat variables. In winter, Kaplan-Meier estimates for subpopulations indicated 2 groups: high (S = 0.991 ± 0.005 [x̄ ± SE]) and low (S = 0.968 ± 0.007) weekly survivorship. Survivorship increased with basal area per hectare of trees, average diameter at breast height of trees, percent cover of slash, and total point-center quarter distance of trees. Cover of grass and forbs were less for the high survivorship than the lower survivorship group. In summer, deer were spaced apart with mixed associations among subpopulations. Habitat manipulations that promote or maintain large trees (i.e., basal area = 14.8 m2/ha and average dbh of trees = 8.3 cm) would seem to improve adult survival of deer in winter.  相似文献   
8.
One of the basal Glyptodontidae groups is represented by the Propalaehoplophorinae (late Oligocene — middle Miocene), whose genera (Propalaehoplophorus, Eucinepeltus, Metopotoxus, Cochlops, andAsterostemma) were initially recognized in Argentinian Patagonia. Among these,Asterostemma was characterized by its wide latitudinal distribution, ranging from southernmost (Patagonia) to northernmost (Colombia, Venezuela) South America. However, the generic assignation of the Miocene species from Colombia and Venezuela (A.? acostae, A. gigantea, andA. venezolensis) was contested by some authors, who explicitly accepted the possibility that these species could correspond to a new genus, different from those recognized in southern areas. A new comparative study of taxa from Argentinian Patagonia, Colombia and Venezuela (together with the recognition of a new genus and species for the Pliocene of the latter country) indicates that the species in northern South America are not Propalaehoplophorinae, but represent the first stages in the cladogenesis of the Glyptodontinae glyptodontids, the history of which was heretofore restricted to the late Miocene — early Holocene of southernmost South America. Accordingly, we propose the recognition of the new genusBoreostemma for the species from northern South America and the restriction ofAsterostemma to the Miocene of Patagonia. Thus, the available data indicate that the Glyptodontinae would in fact have arisen in the northernmost regions of this continent. Their arrival to more southerly areas coincides with the acme of the “Age of Southern Plains”. The Propalaehoplophorinae are geographically restricted to Patagonia.  相似文献   
9.
The Solanum sessile species group is one of eight putatively monophyletic subgroups of the large and diverse Solanum section Geminata. The species group comprises ten species of mostly northern South American trees and shrubs. Characters and character states peculiar to Solanum are discussed in detail. A cladistic analysis of the sessile group yielded four equally parsimonious trees which represent two basic tree topologies. The consensus cladogram is composed of three main clades. Biogeographic analysis using the consensus tree revealed no components in common to the three clades. Possible geographical scenarios are discussed with reference to the geological history of northern South America.  相似文献   
10.
Limited predictability of cyanobacteria and algal harmful blooms (CyanoHABs) impairs the development of adequate water management programs. The Microcystis aeruginosa complex (MAC) is ubiquitous worldwide. Their large colony size and relatively low numerical abundance imply that MAC abundance and presence are usually underestimated in traditional phytoplankton quantifications, which are based on samples of small volume. The objective of this work was twofold: (a) evaluate four sampling strategies of increasing sampling size to detect MAC organisms and (b) asses the predictability of MAC presence using easy-to-measure environmental variables. Sampling strategies were (I) 5–25 mL sedimented water samples inspected under inverted light microscope; (II) 20 L of water samples inspected by on-board naked-eye; (III) samples collected by towing a 25 μm pore size net inspected under light microscope; (IV) naked-eye inspection of 1000–7000 L concentrated water samples collected using a 115 μm-pore plankton net. We evaluated these objectives in a large environmental gradient (800 km) from freshwater to marine water (salinity range = 0–33) covering a wide range of temperatures (10–33 °C), underwater turbidity (0–158 NTU) and wind intensity (0–8 ms−1). Classification Random Forest models (presence/absence of MAC organisms) were constructed and evaluated for each strategy by randomly partitioning data into training (2/3) and test (1/3) sets. A systematic increase in average accuracy (from 51 to 90%) and sensitivity (from 45 to 94%) towards methods with larger sampling size was found (i.e. I–IV). The best obtained model showed a high accuracy (90%) and sensitivity (94%) to detect MAC presence. These results suggest that the presence of MAC organisms can be accurately predicted using easy-to-measure environmental variables once sampling size is adequate. The proposed methodology demands very low costs and could be readily incorporated in most water monitoring plans to provide early warning of MAC occurrence, even when there is a low biomass of organisms.  相似文献   
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