基于种群多样度的变参数遗传算法的研究

该文针对基本遗传算法(SGA)所存在的缺陷——早熟现象进行了分析,并在此基础上提出了基于种群多样度的变参数遗传算法(VPGA)。该算法从概率角度分析了遗传操作算子的作用,搜索范围以及多样性的影响,依据种群的多样度对遗传算法的参数进行自动调节,抑制早熟现象。并应用两种遗传算法对评价遗传算法性能的四个著名测试函数进行了仿真测试,仿真结果表明该算法相对于基本遗传算法的优越性和抑制早熟现象的有效性。

基于改进种群多样度的差分进化算法

针对差分进化算法进化后期易出现早熟收敛而陷入局部最优的缺陷,提出了一种基于改进种群多样度的差分进化算法。对进化算法种群多样度进行了研究,经过数学推导,证明了种群多样度与算法全局寻优性能的关系,提出了一种随机变异策略,更好地保持了寻优过程中种群的多样性,增强算法的全局搜索能力。典型测试函数实验表明,改进后的差分进化算法相对于标准差分进化算法具有更好的种群多样性和抑制早熟收敛的能力。

多样性保持离散差分进化算法及齿轮传动优化应用

将离散约束优化问题转化为等效约束整数规划问题(Constrained integer programming problem,CIPP),并应用离散差分进化(Discrete differential evolution,DDE)算法求解这类问题。提出DDE算法种群维分量一致的概念,并揭示种群维分量呈现一致状态将导致进化停滞的缺陷,数值算例仿真结果验证了理论分析的正确性。在引入定量刻画DDE算法种群多样性指标——种群多样度Γ的基础上,提出一种基于种群连续进化停滞代数和Γ监测的种群多样性保持策略,以克服种群维分量一致进化缺陷,进而增强算法全局优化能力。将多样性保持策略嵌入DDE算法,并结合可行性规则约束处理技术,形成求解CIPP的多样性保持离散差分进化算法(DDE algorithm with diversity maintenance strategies,DMDDE)。建立某刮板输送机所用二级斜齿圆柱齿轮传动体积最小化设计的离散约束优化模型,再采用DMDDE算法求解该问题。数值试验表明,DMDDE算法的鲁棒性和收敛精度优于4种对比算法。优化结果明显好于原设计方案,齿轮体积较原设计下降40.8%。

Distributional patterns of species diversity of main plant communities along altitudinal gradient in secondary forest region,Guandi Mountain,China

Fourteen plots were chosen along with the altitude of 1600-2600 m in Guandi Mountain, Shanxi Province, China to investigate all the trees in the plots, and the species diversity indexes were calculated for analyzing the effects of altitudinal gradient on plant species diversity. The results showed that the order of dominant species from low altitude to high altitude is as Quercus liaotungensis Koidz, Pinus tabulaeformis, Betula platyphylla, B. albo-sinensis, Picea wilsonii, P. Meyeri and Larix principis-rupprechtii. With altitude increasing, the average height and DBH of the arbor firstly increase and then decrease, the maximal height and DBH of the arbor present the unimodal variable trend, the maximal height of coniferous and broad-leaved trees firstly increases and then decreases, the maximal DBH of broad-leaf trees has no clear fluctuation, and the maximal DBH of the needle-leaf trees decreases gradually. Moreover, in middle altitudinal communities （the altitude of 1900-2200 m）, the maximal height and DBH of the needle-leaf trees are larger than these of broad-leaf trees. Both Shannon-wiener index and Margalef index of the communities present the unimodal variable trend, with a peak in the mid-altitude. Plant species diversity in the mid-altitude （1900-2200 m） is higher than that of the low altitude （1600-1900 m） and the high altitude （2200-2600 m）. In addition, the unimodal variable trend of α species diversity is clearly correlated with the altitudinal gradient. The change of plant species diversity is significantly correlated with the altitudinal gradient, and also related to the community structure, the community composition, the feature of species and the human disturbance.

Analysis of the Evolutionary Significance of Heterosis——taking the contribution of fitness to the genetic diversity in random mating population as an example

Upon the analogy of definition of heterosis and inbreeding depresstion in terms of population genetics, the heterosis is thought to be evaluated overall with fitness. By establishing a mathematical model, the equilibrium status of three genotypes of random mating population （i. e. RR, Rr and rr） under different fitness, which exposes that heterosis is the precondition for multiallele to exist in the population. The heterosis protects the genetic diversity and makes the population owning a stronger self-control and evolution potential by improving the hetemzygote＇s fithess so as not to wash out different types of genes. It deepens Darwin＇s thoughts of individual section by making the individual fitness consonant with population fitness.

Floristic and structural analysis of the woodland vegetation around Dello Menna,Southeast Ethiopia

Floristic composition and vegetation structure were described for the woodland vegetation around Dello Menna, Bale zone, southeast Ethiopia. A total 50 （20 m ×20 m） quadrats were sampled to identify and describe plant community types, species diversity, richness and evenness and to relate the identified plant community types with some environ- mental factors and describe the population structure of woody plant species. In each quadrrat, data on species identity, abundance, height and Diameter at Breast Height （DBH） of woody plant species, altitude and slope were recorded. Vegetation classification was performed using PC - ORD software package. Sorensen＇s similarity coefficient was used to detect dissimilarities among communities. Shannon - Wiener diversity index, species richness and Shannon＇s evenness were computed to de- scribe species diversity of the plant community types. Results show that a total of 171 vascular plant species representing 53 families were re- corded. Fabaceae is the dominant family represented by 13 genera and 26 species （15%） followed by Asteraceae, Lamiaceae and Anacardiaceae with eight species each （4.6%）. Based on the results of vegetation classi- fication, three plant communities （Dalbergia microphylla community, Grewia bicolar- Acacia brevispica community, and Combretum molle- Combretum collinum community） are recognized and described. Species richness, diversity and evenness varied among the plant communities.Species richness and diversity exhibit a bell - shaped pattern along alti- tude. Species turn over among communities more or less follow altitud- inal gradients. Tukey＇s pairwise comparison of means among the plant community types shows significant variations in altitude, implying that altitude is one of the most important factors determining the distribution of plant communities. The community Dalbergia microphylla type exhibits the highest species richness and diversity. Analysis of population structure of the dominant species reveals various patterns. Future research directions and recommendations are suggested for the sustainable utilization.

Characteristics of bird communities between slope and valley in natural deciduous forest, South Korea

Bird communities were surveyed in natural deciduous forest of both slope area and valley area at Mt. Gyebangsan (3740 30 N, 12830 1 E), Gangwon Province, South Korea in winter, spring, summer and autumn from September 2000 to November 2001. The investigating results showed that there existed differences in the bird species composition, richness, bird species diversity, guild structure between slope area and valley area, and the vertical forest structure, especially coverage of understory, and diameter at breast height (DBH) distribution also had significant difference between the two study areas. The differences in habitat structure between the areas are very likely to have influences on how birds used the available habitat.

Understory vascular plant community assembly in relation to time-since-fire and environmental variables in a Chinese boreal forest

Understanding the response of understory vegetation to fire disturbance is vital to biodiversity conservation and management of boreal forests. We surveyed understory vascular plant richness and composition, and measured related environmental variables along a toposequence within three successional stages, initial （3 years post-fire）, early （13 years post-fire） and late （〉1oo years post-fire） successional stages. Using permutation multivariate ANOVA and nonmetric multidimensional scaling, we analyzed how understory species richness and composition change as time-since-fire proceeds, and their correlative relationships with environmental variables. Species richness and composition showed significant differences among the three successional stages. Understory species richness and abundance were significantly associated with time-since-fire, topographic position, elevation and organic layer depth. Among these variables, time-since-fire had the strongest effect and topographic position was the second major factor on affecting understorycommunity assembly. In overwhelmed the effects addition, time-since-fire of soil pH in the initial successional stage and gravimetric soil moisture in early and late successional stages on understory species composition

Cultivable Microfungal Communities Inhabiting Biological Soil Crusts in the Tengger Desert, China

Biological soil crusts are essential components of arid ecosystems. We examined the variations in microfungal communities inhabiting different biological crust types in the vicinity of the Shapotou Research Station in the Tengger Desert, China. A total of 134 species from 66 genera were isolated using the soil dilution plate method. The mycobiota of the crusts from the Tengger Desert, similar to that of the Negev Desert in Israel, was dominated by melanin-containing species with large multicellular spores. Abundance of these xeric species increased spatially with increasing xeric conditions from moss-dominated to cyanobacterial crusts. Density of microfungal isolates displayed the opposite trend and was positively correlated with chlorophyll content, indicating the possible significant influence of organic matter content and wetness duration on fungal biomass. Within a chronosequence of the localities of different periods after sand stabilization with revegetation, little variations were revealed in species composition and isolate density of the crust microfungal communities, while a tendency towards a decrease in the community diversity level with the crust age was noted Microfungal communities from stabilized localities differed from those of the natural localities in abundance of the dominant and some frequent species, and in the fluctuations of diversity characteristics between the cyanobacterial and moss-dominated crusts. The variations in mycobiotie parameters in the soil crusts of the Tengger Desert were apparently associated with the topographically induced variations in abiotic conditions, while the differences in microfungal community of soil crusts between the Tengger and Negev deserts, such as the significantly higher abundance of thermotolerant species in the crusts of the Tengger Deserts, were caused by the principal differences in their precipitation regimes, associated with different rainy seasons, winter and summer in the Negev and Tengger deserts, respectively.