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61.
桂花在园林景观设计中的应用 总被引:2,自引:0,他引:2
对桂花植物造景的配置原则、园林应用进行概述和研究,提出因地制宜、层次错落、季相变化、背景烘托、民族传统的配置原则,并就园林应用上桂花的独立造景,桂花与其他植物的配置,桂花与山石、建筑物的配置作了分述。 相似文献
62.
谢德琼 《四川畜牧兽医学院学报》2005,3(4):133-136
讨论了目前大学英语课程设置单一的现状,并分析其形成原因。文章以ESP研究关于需求分析的理论为依据,提出大学应根据学生的实际需要、新时期国家和社会对人才培养需要,区别不同层次、不同程度、不同专业学生的需求,而专门设置一系列大学英语课程。说明了设置个性化的大学英语课程的理由和好处。 相似文献
63.
The influence of sampling scheme and interpolation method on the power to detect spatial effects of forest birds in Ontario (Canada) 总被引:1,自引:0,他引:1
Spatial ecology is becoming an increasingly important component of resource management, and the general monitoring of how
human activities affect the distribution and abundance of wildlife. Yet most work on the reliability of sampling strategies
is based on a non-spatial analysis of variance paradigm, and little work has been done assessing the power of alternative
spatial methods for creating reliable maps of animal abundance. Such a map forms a critical response variable for multiple
scale studies relating landscape structure to biotic function. The power to reconstruct patterns of distribution and abundance
is influenced by sample placement strategy and density, the nature of spatial auto-correlation among points, and by the technique
used to extrapolate points into an animal abundance map. Faced with uncertainty concerning the influence of these factors,
we chose to first synthesize a model reference system of known properties and then evaluate the relative performance of alternative
sampling and mapping procedures using it. We used published habitat associations of tree nesting boreal neo-tropical birds,
a classified habitat map from the Manitou Lakes area of northwestern Ontario, and point count means and variances determined
from field studies in boreal Canada to create 4 simulated models of avian abundance to function as reference maps. Four point
sampling strategies were evaluated by 4 spatial mapping methods. We found mixed-cluster sampling to be an effective point
sampling strategy, particularly when high habitat fragmentation was avoided by restricting samples to habitat patches >10
ha in size. We also found that of the 4 mapping methods, only stratified ordinary point kriging (OPK) was able to generate
maps that reproduced an embedded landscape-scale spatial effect that reduced nesting bird abundance in areas of higher forest
age-class fragmentation. Global OPK was effective only for detecting broader, regional-scale differences.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
64.
Assessing the potential impacts of alternative landscape designs on amphibian population dynamics 总被引:2,自引:1,他引:2
An individual-based, spatially explicit population model was used to predict the consequences of future land-use alternatives for populations of four amphibian species in two central Iowa (midwest USA) agricultural watersheds. The model included both breeding and upland habitat and incorporated effects of climatic variation and demographic stochasticity. Data requirements of the model include life history characteristics, dispersal behavior, habitat affinities, as well as land use and landcover in geographic information systems databases. Future scenarios were ranked according to change in breeder abundance, saturation, and distribution, compared to baseline conditions. Sensitivity of simulation results to changes in model parameters was also examined. Simulated results suggest that while all four species modeled are likely to persist under present and future scenario conditions, two may be more at risk from future landscape change. Although the study species are all widespread generalists regarded as having a low conservation priority, they depend on wetlands and ponds, increasingly endangered habitats in agricultural landscapes. Broader conservation strategies in the region would ensure that these currently common organisms do not become the endangered species of the future.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
65.
A mathematical model has been developed for the risk assessment of the spread of genes conferring herbicide resistance in plant populations. The model combines an age-and-stage-structured population dynamic model, a population genetic model and a model of spatial spread. This is achieved by embedding a local matrix population model into a cellular automaton model with raster cells as spatial units. The dynamics of each cell is determined by both its local dynamics and the interaction with neighbouring cells. The model is applied to the evaluation of management strategies to delay or even to prevent long-term evolution of resistance in an annual grass weed. The results show that the appearance and spread of resistant genes is a highly non-linear process exhibiting threshold phenomena, which occur for a wide range of parameters. The properties of the seed survival curve constitute the `genetic memory' of the system and thus determine its long-term dynamics. It is possible to delay the evolution of resistance by suspension of treatment, reduction in herbicide application rate and introducing fallow periods. Spatial spread from an infested plot is inhibited by leaving untreated strips between adjacent fields. 相似文献
66.
A simple life-cycle-based demography model was adapted for two contrasting weed species ( Alopecurus myosuroides and Poa annua ). This model included a seed production function that accounted for population self-regulation through weed:weed interactions. The A. myosuroides version of the model was tested with field data. Long-term simulations of population demography were then performed to investigate the relationship between weed control strategies based on density thresholds and both the frequency of herbicide use and the long-term economic profitability. This study confirms that threshold-based weed management strategies are more cost-effective than spraying every year and may allow important reductions in herbicide use. However, after the first transient years of either systematically spraying or withholding herbicide, the long-term spraying frequency was insensitive to threshold values between 0.01 and 100 plants m−2 . The highest long-term profitability was obtained for the lowest threshold tested, and the profitability decreased rapidly when the threshold was raised above 4–6 and 10–20 plants m−2 for A. myosuroides and P. annua respectively. The study thus indicates that the exact threshold value is of little importance for the long-term reliance of the system on herbicide, provided that it is reasonably low. For species with low competitive ability, high thresholds may be used in some cropping systems to reduce the spraying frequency for environmental considerations, but those options would also reduce the profitability if no compensatory measures were taken. 相似文献
67.
Genetic diversity in populations of the fungi Phaeomoniella chlamydospora and Phaeoacremonium aleophilum on grapevine in France 总被引:4,自引:0,他引:4
B. Borie L. Jacquiot I. Jamaux-Despréaux P. Larignon J.-P. Péros † 《Plant pathology》2002,51(1):85-96
Isolates of Phaeomoniella chlamydospora ( Phc ) and Phaeoacremonium aleophilum ( Pha ), two haploid, deuteromycetous fungi, were obtained from vines showing symptoms of esca disease in different localities in two French regions, and within a single vineyard in one of these regions. The population genetic structure was determined in both fungi using random amplified polymorphic DNA (RAPD) analysis. Populations of Phc showed similar levels of diversity at local and regional levels. The most frequent Phc haplotypes were found in every population, and the frequencies of positive alleles of markers were similar across populations. The hypothesis that recombination had occurred was rejected for the full set of samples, but not for the samples reduced to haplotypes, indicating that Phc may be a recombining species. Different features were identified in Pha populations. First, the southern population of Pha appeared more diverse than the south-western populations. Second, genetic differentiation was identified between Pha populations from southern and south-western regions for several RAPDs. Finally, in the southern population of Pha no evidence for recombination was obtained, even by reducing the sample to haplotypes. Within the single vineyard surveyed, several haplotypes of both fungi were recovered and randomly distributed. Thus different infection events appeared to have occurred on a low spatial scale. Data from this study showed that haplotypes of both fungi were distributed over long distances geographically, and that most of the vineyards surveyed were infested by more than one haplotype of Phc and Pha . 相似文献
68.
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70.
采用均匀设计法优化红汁乳菇液体深层发酵培养基。结果表明,最佳培养基配方是:蔗糖34g]L,废糖蜜13mL/L,麸皮36g/L,玉米粗粉20g/L,KH2PO43g/L,菌丝体最大生物量达18.087g/L。 相似文献