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41.
The parsimony and bootstrap branching pattern of major groups of land plants derived from relevant 5S rRNA sequence trees
have been discussed in the light of paleobotanical and morphological evidences. Although 5S rRNA sequence information is not
useful for dileneating angiosperm relationships, it does capture the earlier phase of land plant evolution. The consensus
branching pattern indicates an ancient split of bryophytes and vascular plants from the charophycean algal stem. Among the
bryophytes,Marchantia andLophocolea appear to be phylogenetically close and together withPlagiomnium form a monophyletic group.Lycopodium andPsilotum arose early in vascular land plant evolution, independent of fem-sphenopsid branch. Gymnosperms are polyphyletic; conifers,
Gnetales and cycads emerge in that order with ginkgo joiningCycas. Among the conifers,Metasequoia,Juniperus andTaxus emerge as a branch independent ofPinus which joins Gnetales.
The phylogeny derived from the available ss-RNA sequences shows that angiosperms are monophyletic with monocots and dicots
diverging from a common stem. The nucleotide replacements during angiosperm descent from the gymnosperm ancestor which presumably
arose around 370 my ago indicates that monocots and dicots diverged around 180 my ago, which is compatible with the reported
divergence estimate of around 200 my ago deduced from chloroplast DNA sequences.
Since deceased. 相似文献
42.
Justification of a simple and reliable relativistic procedure for the prediction of a large body of transition probability data is made. The main features of the Relativistic Quantum Defect Orbital (RQDO) formalism are described, and several examples of the data yielded by this method are presented in tabular and graph forms. 相似文献
43.
目的:制备担载血管生长因子(VEGF)的乳液法静电纺丝纤维膜,对其开展一系列表征,从而研究其血管再生的潜能。方法:通过W/O乳液法制备担载VEGF的静电纺丝纤维膜,并对其形态、力学性质进行表征。用VEGF ELISA分析方法对其体外释放动力学进行研究。运用CCK-8法检测乳液法静电纺丝纤维膜中VEGF的活性变化。结果:乳液法静电纺丝纤维膜呈现连通的三维网状结构,平均直径为1μm,模拟了细胞外基质(ECM),最大拉伸应力为3.03±0.66 M Pa,具有良好的抗拉伸能力,能够支持细胞的生长。乳液法纤维膜中VEGF在体外累积释放了14天,总释放量超过20000 pg,达到血管再生的有效浓度。CCK-8结果显示,乳液法纤维膜中的VEGF仍然保持较高的蛋白活性。结论:担载VEGF的乳液法静电纺丝纤维膜能够缓释出活性的蛋白,具有血管再生的潜能。 相似文献
44.
45.
Qinfeng Guo 《Biological invasions》2006,8(7):1451-1459
The effectiveness of management strategies for invasive species is often hampered by a lack of clear understanding of the
factors that limit species distributions. The distribution of exotic species, especially those that are invasive, are often
so dynamic that limiting factors are difficult to identify. Comparisons of exotic species between their native ranges, where
they are presumably close to equilibrium with controlling factors, and their ranges in areas of introduction can circumvent
this difficulty. Such studies would help identify (1) limiting factors for distributions in native ranges, (2) factors associated
with a high degree of invasiveness, (3) changes in genetics and morphology since introduction, which also might contribute
to invasiveness, and (4) future directions and rates of invasion as a basis for developing detection/warning systems. Findings
from such comparative studies would be highly valuable for understanding the dynamics of biological invasions and for improving
the effectiveness of management to prevent or control invasives. 相似文献
46.
Multi-mesh gillnets to estimate species composition and catch per unit effort of fish in a small water body in Zambia 总被引:1,自引:0,他引:1
A standard method comprising multi-mesh monofilament nylon gillnets and depth stratification, the Drottningholm method, was employed in test fishing of a small Zambian reservoir (32 ha) on eight occasions over 1 year. The catch per unit effort (cpue) from the 0–3 and 3–6 m zone was timated with benthic and pelagic nets, while in the 6–12 m zone only benthic nets were used. Results include species caught and cpue with coefficients of variation and confidence intervals, for net types and depth zones. A total of 11 species were caught, of which Burbus paludinosus , B. marequensis , Laheo cylindricus , and Oreochromis sp. dominated. Coefficients of variation did not indicate a preferable season for test fishing. During the cold season some species were not caught. The applicability of the method in estimation of species composition and cpue is discussed. 相似文献
47.
Aim Species capable of vigorous growth under a wide range of environmental conditions should have a higher chance of becoming invasive after introduction into new regions. High performance across environments can be achieved either by constitutively expressed traits that allow for high resource uptake under different environmental conditions or by adaptive plasticity of traits. Here we test whether invasive and non‐invasive species differ in presumably adaptive plasticity. Location Europe (for native species); the rest of the world and North America in particular (for alien species). Methods We selected 14 congeneric pairs of European herbaceous species that have all been introduced elsewhere. One species of each pair is highly invasive elsewhere in the world, particularly so in North America, whereas the other species has not become invasive or has spread only to a limited degree. We grew native plant material of the 28 species under shaded and non‐shaded conditions in a common garden experiment, and measured biomass production and morphological traits that are frequently related to shade tolerance and avoidance. Results Invasive species had higher shoot–root ratios, tended to have longer leaf‐blades, and produced more biomass than congeneric non‐invasive species both under shaded and non‐shaded conditions. Plants responded to shading by increasing shoot–root ratios and specific leaf area. Surprisingly, these shade‐induced responses, which are widely considered to be adaptive, did not differ between invasive and non‐invasive species. Main conclusions We conclude that high biomass production across different light environments pre‐adapts species to become invasive, and that this is not mediated by plasticities of the morphological traits that we measured. 相似文献
48.
The Anderson-Kannemann test is a rank test for treatment effects in a randomized block design with K treatments and N blocks. In this paper, an algorithm for computing the exact distribution of the Anderson-Kannemann test statistic under the null hypothesis is deduced. Then, the exact distribution is compared with the asymptotic χ2-distribution, and it is shown that the exact distribution is approximated fairly well by the asymptotic distribution. Tables of the exact distribution are given for K = 3, N = 3(1)15; K = 4, N = 3(1)11; K = 5, N = 3(1)7; and K = 6, N = 3(1)5. 相似文献
49.
50.
We propose in this work a novel approach aiming at assessing cause and effect relationships between variables that can affect target biodiversity issues. These cause–effect relations are used to build a network whose nodes represent variables linked by directed arcs. The arcs have associated a value that represents trends of cause–effect relations. An important novelty of this approach is the use of product and addition operations between trends of cause–effect relations for assessing factors that can affect target variables. For the analysis of the network we use the concept of paths. Paths are defined as sequences of cause–effect relations from source variables to target variables. For example, the path from population increment that causes effects on the increment of transport routes, which in turn causes effects on the loss of vegetation cover. This approach was applied to the assessment of vegetation cover in the Morelos State, México during the period 2000–2010. The results show a promising practical alternative to assess the potential effects on biodiversity issues based on the analysis of the paths represented in the network. 相似文献