Predictive models of weed population dynamics

Many of the challenges faced by weed ecologists can be met only by the capability to predict the responses of weed populations to changes in their environment or management. In spite of this, a review of papers published in Weed Research suggests that weed ecologists are remarkably reluctant to produce detailed, quantitative predictions. This may result from uncertainty in the accuracy of predictions and indeed, a variety of reasons have been put forward to suggest that the potential utility of weed models may be limited in this regard. In this study, we review the applications to which weed models have been put. Focusing on predictive population modelling, we highlight several limitations that can lead to failures of this approach and we discuss the likely prospects for weed population modelling. We make three points regarding the future of weed modelling. First, owing to prohibitive data requirements, the development of highly mechanistic models that attempt to make detailed predictions of weed population numbers is unlikely to be very successful. Second, data collection for developing weed models needs to be rethought. Weed models are most commonly compromised by a lack of spatial and temporal replication, preventing modellers from measuring parameter variability and error effectively and limiting assessments of model uncertainty. Finally, the utility of models needs to be better appreciated; models are key tools in making long range predictions of how management will affect weed populations, but, we estimate, they are used in only a small fraction of studies. Without the further development of models for weed population dynamics, our ability to predict long-term dynamics will be restricted.     

新疆未来人口发展趋势研究

人口因素是社会经济发展的重要因素,人口的增长趋势将影响到未来社会经济的可持续发展.根据2000年新疆人口普查资料,采用队列法、Gm(1,1)模型对新疆2010年至2040年人口结构进行预测,分析新疆未来人口发展趋势及社会影响,并对相关问题提出了针对性的政策建议.     

新疆人口结构分析

据全国历次人口普查资料,对新疆人口的自然、社会、经济以及地域结构进行深入分析,揭示新中国成立以来在新疆人口结构中所发生的重要变化。分析结果表明:新疆人口的性别比正处于正常状态,年龄结构上步入成年型;民族结构上虽然少数民族人口占新疆总人口中的比重下降,可是各少数民族总人口数量不断上升,而且始终保持新疆总人口中占一半以上比重的状态;随着教育事业的发展,使新疆人口的文盲率大幅度下降,使人均受教育水平大幅度提高;随着经济的发展,新疆总人口中的城镇人口比重逐渐上升;经济结构的变化表明,第一产业就业人口在总就业人口中的比重明显下降,第三产业就业人口在总就业人口中的比重大幅度提高;职业结构方面,新疆总人口中从事体力工作的劳动者比重较高,其中从事农林牧渔劳动者比重较大,始终保持在60%以上。     

Characterization of theErwinia amylovora population in Israel

A collection of 205 strains ofErwinia amylovora isolated in Israel over a period of 12 years has been established. The strains were isolated from different varieties of pear, apple, loquat and quince grown in Israel, and collected from different locations in the country. They were characterized in respect to degree of virulence on several hosts and serological and molecular characters. Pathogenicity tests carried out on flowering branches of pear and apple, shoots of pears, and on trees of pear and loquat grown in containers outdoors, revealed no significant differences in the severity of blossom blight or shoot blight among the various strains. ELISA and immunofluorescence assays revealed no serotypic groups among the Israeli strains. Genomic diversity was studied by random amplified polymorphic DNA (RAPD) analysis using 24 arbitrary 10-base primers. All the strains examined (45 Israeli and 11 from Egypt, Cyprus and Greece) produced the same RAPD patterns with each of the primers used. Amplification patterns were indistinguishable from those produced by strains isolated from the neighboring countries. Results presented in this study suggest that the population ofE. amylovora in Israel is homogenous.     

Structure of the Cochliobolus sativus population variability

The genetic diversity of several local populations of the fungal pathogen Cochliobolus sativus, collected over 3 years from different regions of the Czech Republic, was examined using amplified fragment length polymorphism (AFLP). A high level of variability was found even among isolates from one lesion. Measures of multilocus linkage disequilibrium suggested that recombination has a minor impact on the genetic structure of populations. Cochliobolus sativus forms genetically divergent populations (F_ST = 0·33), indicating a low level of geneflow between populations. This was supported by a significant correlation between genetic diversity and geographical distances up to 80–100 km. The most likely explanation for the genetic variability is that the fungus forms conidia with highly variable chromosomal rearrangements. The differentiation observed among local populations implies that genetic drift, including a founder effect, combined with restricted migration generates the structure of C. sativus populations.     

1990-2010年西北地区县域人口数量与空间集疏变化时空分析

基于分县人口普查数据,对1990年以来西北地区县域人口数量增减和人口空间集疏变化情况进行了时空分析。通过研究认为:1)西北地区人口总量继续增加和空间分布不均衡的格局态势仍将延续;2)人口显著增加(或流入)地区和一般减少(或流出)地区人口比例均有所增加;3)人口数量增减趋于频繁,人口空间集疏过程日趋激烈;4)自然环境和经济发展决定人口数量增减和空间集疏变化;5)地级市辖区及其周边人口变化最为激烈,城市必将成为未来吸纳西北人口集聚的主要载体,但人口外迁趋势也在所难免。     

黏虫种群雌虫率与其数量趋势指数关系的研究

通过对蒙城县植保站27a黏虫资料的研究分析,可以看出一代黏虫多年雌虫率的平均值应是最佳雌虫率。一代黏虫种群的雌虫率愈接近最佳雌虫率,其下代种群数量趋势指数则越高;反之,则较低。     

北疆城镇区域人口发展中的问题及人口空间分布特征

北疆城镇区域是新疆人口最为密集、经济最为发达的城镇密集地区,但其在人口发展过程中过快的人口增长、过低的人口素质、分布广和数量多的贫困人口及少数民族人口等诸多问题已经极大地制约了区域经济的发展步伐。文中通过相关数据的整理和分析,得出北疆城镇区域的人口空间分布总体上具有首位度高、不均衡及人口规模体系不健全等特点,同时深入分析了区域人口密度分布独特的马鞍状分布特点。     

基于县域单元的中国人粮关系及其变化研究

以基于县域尺度的1980年、1990年、2000年的统计资料为基础,采用人口粮食匹配曲线、基尼系数等指标,分析计算中国县域尺度的人口粮食关系,揭示中国县域人-粮关系及其演变规律,旨在为统筹解决国家粮食安全问题提供科学依据。研究结果表明：1）1980-2000年我国人口粮食匹配不均衡程度越来越高,一方面说明我国粮食生产集...     

稻瘟病菌群体育性分析的主要影响因子研究

 将稻瘟病菌10个两性可育菌株,包括GUY11、KA3、KA9、KA7、6023、2539W、8773R-19、8773R-27、8113R-2和8113R-10相互交配,结果表明,10个菌株育性好,交配型明确;2539W已丧失雌性功能,不再是两性菌株。原先由6023/2539W测为可育的24个福建省田间稻瘟病菌菌株分别与另外8个两性菌株交配,结果得出不同两性菌株测得同一组稻瘟病菌菌株的育性差异很大,这可能是由于两性菌株的交配能力强弱差异以及两性菌株与待测菌株之间的亲和性不同引起的。分析认为,GUY11和KA3最适于测定稻瘟病菌群体的育性和交配型,并用其测定了227个来自福建省田间稻瘟病菌菌株的育性。结果表明,福建省稻瘟病菌群体可育菌株率为81.1%,其中81.0%为交配型MAT1-2,19.0%为MAT1-1。研究结果将有助于进一步认识稻瘟病菌的群体结构特点及其演化规律。     

内分泌干扰不育在兽类种群控制中的应用

随着传统害兽种群控制方法弊端的暴露,不育控制愈来愈受到关注。不育控制的策略可分为手术/化学不育、内分泌干扰不育和免疫不育。针对研究应用较多的内分泌干扰不育剂,从其种类、不育机理、给药方式和不育效果4个方面,阐述国内外不育控制害兽的研究进展;着重介绍各种不育剂的药效;并对该领域存在的问题提出建议,认为应加强理想不育剂的开发和不育剂对兽类领域行为的研究。     

内蒙古人口发展功能分区研究

以分县为基本单元,根据人居环境的自然适宜性、资源环境承载力和发展潜力、物质积累基础和人类发展水平,结合国家安全战略与内蒙古区域发展战略,采用基于G IS的多因素迭置模型和基于决策树的定量化分析方法,编制了内蒙古人口发展功能分区方案,在此基础上,提出了统筹不同类型区人口与资源环境协调发展的战略选择及政策建议。研究表明:内蒙古人口发展功能区以人口限制区为主要组成部分,其次是人口发展疏散区和稳定区;内蒙古人口稳定区以呼包鄂、通辽、赤峰等城市群为主要形态,人口与资源环境经济社会发展基本协调,人口具有一定的发展空间;人口疏散区以丰镇、克什克腾等中、小城市和乡、镇为主要形态,人口与资源环境经济社会发展相对推移,未来人口发展应相对集中,适度疏散;人口限制区以阿尔山、额尔古纳等小城镇和乡村发展为主要形态,人口与资源环境经济社会发展失衡。未来应有计划实施人口迁移和生态移民,建设国家生态屏障,促进不同地区人口与资源环境经济社会协调发展。     

侧多食跗线螨实验种群生命表的研究

侧多食跗线螨是我国蔬菜重要害螨之一。通过对该螨在取食茄子条件下实验种群生命表的研究,结果表明：该螨的内禀增长率（ｒ_ｍ）、周限增长率（λ）、净增殖率（Ｒ_ｏ）、种群世代平均周期（Ｔ）和种群加倍时间（ｔ）分别为０.２５８４、１.２９４８、１９.３９５３、１１.４７２８和２.６８２３。     

菱角小萤叶甲种群动态研究

对菱角小萤叶甲在菱塘的发生数量调查和分析表明,菱角小萤叶甲种群数量在一年中春末夏初和夏末秋初各有一个高峰期。温度是影响菱角小萤叶甲种群数量消长的关键因子;聚集度指标的分析表明,菱角小萤叶甲在菱塘呈聚集分布。聚块性指标与平均密度独立,适合用于分析菱角小萤叶甲分布型的时序变化;在控制条件下菱角小萤叶甲种群动态的研究表明,该虫具有较强的种群数量调控能力。     

小麦条锈菌群体温度敏感性测定

小麦条锈病由小麦条锈菌(Puccinia striiformi Westend.)引起,该病害发生范围广、流行频率高、危害损失重.小麦条锈菌侵染与繁殖均需要较低温度,过去研究表明,条锈菌在夏季最热旬均温23℃以下地区才能越夏[1].近年调查研究发现,小麦条锈菌的越夏海拔下限明显降低,病菌在夏季最热旬的旬均温超过23℃的地区也能越夏.研究不同地区和不同年代小麦条锈菌群体对温度的敏感性,有助于了解温度对条锈菌群体进化的影响,明确在小麦条锈菌群体中是否产生了耐高温菌株,为小麦条锈病菌源区勘界、病害流行测报等提供科学依据.本文报道了对小麦条锈菌群体温度敏感性的初步研究结果. 1 材料与方法 1.1试验材料 1.1.1供试菌株采自全国不同流行区、不同年代的小麦条锈菌标样,经分离纯化后获得126个条锈菌菌株.     

Dynamic multiline population approach to resistance gene management

ABSTRACT The dynamic multiline population breeding strategy integrates principles from the gene stacking and multiline approaches and allows application of the multiline strategy to cross-pollinated hybrid crops. Experiments were conducted to evaluate the effectiveness of the breeding approach. Backcross derivatives of pearl millet Tift 23DB were developed with rust resistance from 18 Burkina Faso landraces, 3 Pennisetum glaucum subsp. monodii accessions, and 2 elite inbreds (1 from India and 1 from the United States). Four cycles of open pollination were made, the last two in the field in rust epidemics. Cytoplasmic male-sterile (CMS) counterparts of the populations in the A(4) cytoplasm were included and advanced simultaneously with the B population. Hybrids with Tift 383 were produced on CMS cycles 1 (C1) through C4. Frequency of hybrid seedlings with resistance increased with each cycle, and frequencies averaged 18 to 38% in C1 to C4 hybrids, respectively, when inoculated with five single-uredinium isolates of Puccinia substriata var. indica. The hybrid populations and Tifleaf (TL)1 and TL2 were evaluated in three yield trials in 1998 to 1999. Disease-free forage dry matter yields did not differ among hybrids. Across trials, area under the disease progress curve (AUDPC) of TL1 and TL2 averaged 1,307, C1 and C2 averaged 914, and C3 and C4 averaged 604. Final severities of TL1 and TL2 averaged 67%, C1 and C2 averaged 47%, and C3 and C4 averaged 30%. When analyzed by regression analysis, AUDPC was reduced 12.2%, final rust severity was reduced 13.3%, and digestible biomass was increased 4.1% per cycle.