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951.
Using shotgun sequencing data, the complete sequences of chloroplast 16S rRNA and tufA genes were acquired from native specimens of Bryopsis hypnoides (Qingdao, China). There are two group I introns in the 16S rRNA gene, which is structurally similar to that of Caulerpa sertularioides (Bryopsidales, Chlorophyta). The chloroplast-encoded tufA gene sequence is 1 230 bp long, very AT-rich (61.5%), and is similar to previously published 16S rRNA sequences of bryopsidinean algae. Phylogenetic analyses based on chloroplast 16S rRNA and tufA gene sequence data support previous hypotheses that the Bryopsidineae, Halimedineae, and Ostreobidineae are three distinct lineages. These results also confirmed the exclusion of Avrainvillea from the family Udoteaceae. Phylogenetic analyses inferred that the genus Bryopsis as sister to Derbesia; however, this clade lacked robust nodal support. Moreover, the phylogenetic tree inferred from rbcL GenBank sequences, combined with the geographical distributions of Bryopsis species, identified a strongly supportive clade for three differently distributed Asian Bryopsis species. The preliminary results suggesting that these organisms are of distinct regional endemism. 相似文献
952.
军曹鱼群体遗传结构的AFLP分析 总被引:1,自引:0,他引:1
筛选出10对扩增片段长度多态分析技术(Amplified fragment length polymorphism,AFLP)的选择性扩增引物(E-aga/M-cgt、E-aga/M-cga、E-agc/M-cga、E-agg/M-cga、E-act/M-cgc、E-aag/M-cgc、E-aca/M-cga、E-aac/M-cgc、E-aac/M-cac和E-aac/M-cat),分析了4个军曹鱼(Rachycentron canadum)全人工繁育群体海南1(HN1)、海南2(HN2)、湛江(ZJ)和流沙湾(LS)的遗传结构。结果表明:总体多态位点比例(83.9%)、分化指数(0.427 8)和Shannon信息指数(0.614 9)均处于较高水平,遗传多样性丰富;主坐标分析和邻位连接树中LS-HN2支与ZJ-HN1支明显分离,各群体内多样性水平存在差异(遗传多样性大小依次为HN1、HN2、LS、ZJ),但总体基因流仍然较大(Nm=10.327),分子方差分析(AMOVA)获得的群内方差(53%)也略大于群间(47%)。 相似文献
953.
954.
城镇化水平测定方法构建与案例 总被引:1,自引:0,他引:1
城镇化水平作为衡量一个国家和地区城镇化的指标,其测定方法还不甚完善,对其进行研究成为科学评价我国城镇化水平的一个重要课题。城镇与乡村最直观的区别在于人口的集聚程度、人口的职业构成、土地的利用方式,因此,在既有城镇地域界定标准的基础上,选择人口密度、非农业人口比重、建成区面积比重、人均耕地面积等指标作为判断不同政区是否成为城镇地域的基本指标。通过层层设置临界值,合理地界定了城镇地域范围,并核定了城镇人口,为科学计算城镇化水平提供了依据。以曲阜市为实例,对上述标准进行检验,结果表明,这种城乡划分标准合理,结果符合实际,同时计算简便,利于应用。 相似文献
955.
956.
中国流动人口地域类型——划分方法及空间分布(英文) 总被引:3,自引:3,他引:0
With the rapid increase of the number and influence of floating population in China,it is urgently needed to understand the regional types of China’s floating population and their spatial characteristics. After reviewing the current methods for identifying regional types of floating population,this paper puts forward a new composite-index identification method and its modification version which is consisted of two indexes of the net migration rate and gross migration rate. Then,the traditional single-index and the new composite-index identification methods are empirically tested to explore their spatial patterns and characteristics by using China’s 2000 census data at county level. The results show:(1) The composite-index identification method is much better than traditional single-index method because it can measure the migration direction and scale of floating simultaneously,and in particular it can identify the unique regional types of floating population with large scale of immigration and emigration. (2) The modified composite-index identification method,by using the share of a region’s certain type of floating population to the total in China as weights,can effectively correct the over-or under-estimated errors due to the rather large or small total population of a region. (3) The spatial patterns of different regional types of China’s floating population are closely related to the regional differentiation of their natural environment,population density and socio-economic development level. The three active regional types of floating population are mainly located in the eastern part of China with lower elevation,more than 800 mm precipitation,rather higher population densities and economic development levels. 相似文献
957.
This paper calculated spatial accessibility of all counties (city, urban district) in China with cost weighted distance method. Region divisions of county accessibility were conducted, and relation of traffic accessibility and population aggregation was discussed in this paper. The results indicated that county accessibility in China had mainly low values and a distribution structure of circle layer and reverse-to-natural gradient. There was an obvious correlation between county accessibility and population density in China. With these analyses, inner mechanisms of population migration in different traffic conditions and region types were revealed, and can provide useful proposals to regional planning, traffic planning and smart distribution of people in China. 相似文献
958.
R.M. Portilla-AlonsoC. Martorell 《Journal of Arid Environments》2011,75(6):509-515
Cacti are thought to be highly vulnerable to chronic anthropogenic disturbance (CAD). To assess its effects, we modeled the dynamics of three populations of the endangered cactus Coryphantha werdermannii exposed to different intensities of disturbance. Because no seedlings germinated and survived in the less-disturbed site, we analyzed two different scenarios: If the same, average germination probability was used for all sites, the population growth rates (λ) decreased with disturbance, but λ remained unchanged if a very low germination probability was assigned to the less-disturbed site and the observed probabilities were used for the remaining populations. Retrospective analysis showed that different demographic processes affected λ as a result of increasing disturbance: The unsuccessful establishment of seedlings in the preserved site diminished λ. The damage caused by livestock to reproductive structures in the site with intermediate disturbance was responsible for a reduction in λ. In the most disturbed site, the reduced individual growth rates that seemingly resulted from land degradation caused a decrease in λ. No simple management strategy can be proposed because different threats require attention depending on disturbance intensity. CAD had both positive and negative effects on λ, conferring this species with a certain degree of tolerance. 相似文献
959.
An explicit formula is developed to explore the mechanism of the synchrotron radiation by using a bi-modal loss-cone distribution function. The variation of the distribution function along the field line is modeled in detail and the evaluation of the total power in the synchrotron radiation is presented. The variance of synchrotron radiation with latitude depends on the electron anisotropy; for low anisotropy, synchrotron radiation increases with latitude and reaches a maximum at the particle mirror points; for high anisotropy, it decreases with latitude and maximizes at the equator. A bi-modal population is therefore suggested to explain the radiation intensity which peaks both at the equator and at high latitude. 相似文献
960.
利用常微分方程的定性理论,研究了两个种群具有非线性密度制约的捕食-被捕食者系统:dxdt=b0x(b1+b2x-b3x2)-b4xy,dydt=-cy+(αx-βy)y,的平衡点的性质,并证明了该系统存在唯一极限环的一个充分必要条件。 相似文献