Population fluctuation and persistence of one-host–two-parasitoid systems depending on resource distribution: from parasitizing behavior to population dynamics

Population dynamics and variability were examined in one-host–two-parasitoid experimental systems with different resource distributions: resource-clumped and resource-sparse conditions. The system consists of a seed beetle host, Callosobruchus chinensis, and two parasitoid wasps, Anisopteromalus calandrae (Pteromalidae) and Heterospilus prosopidis (Braconidae). In the resource-clumped condition, suitable hosts for parasitism (the late fourth-instar larvae and pupae) were clumped in 1 large resource patch, but they were scattered evenly among 16 small patches in the resource-sparse condition. Population censuses were conducted at 10-day intervals in long-term cultures, renewing 10 g of azuki beans (Vigna angularis). In both resource conditions, the first period was a single-species system of C. chinensis only, and A. calandrae was added in the second period. The one-host–one-parasitoid system with C. chinensis and A. calandrae showed stable population dynamics with small fluctuations. After addition of H. prosopidis in the third period, two of three replicates persisted to day 800 in each resource condition, although one replicate in each went to extinction at an immediate outbreak of the H. prosopidis population after the introduction. Population variabilities of C. chinensis and H. prosopidis were significantly higher and the mean population size of A. calandrae was significantly smaller in the resource-sparse condition than that in the resource-clumped one. A short-term experiment on parasitism efficiencies revealed that H. prosopidis parasitized significantly more at a low host density in the resource-sparse condition than in the resource-clumped one. Mutual interference of H. prosopidis was weak enough at low parasitoid densities but became abruptly stronger with high densities. Providing fresh hosts in a mixture of already parasitized ones, host-searching behaviors of a parasitoid were recorded by video for 3 h and were compared between the two wasp species. H. prosopidis could parasitize fresh hosts more efficiently than A. calandrae through frequent long-distance walks (walking to distant beans at one bout or outside a clump of beans with hosts and back soon on a distant bean of the clump) after reencounters with parasitized hosts. Considering all the experimental results, populations were judged to be more fragile and more likely to go to extinction in the resource-sparse condition than in the resource-clumped one. A higher attacking efficiency of H. prosopidis destabilized population dynamics more in the resource-sparse condition. Received: December 23, 1998 / Accepted: January 20, 1999     

论汉语复合词的语言价值

汉语复合词是在古代单音词的基础上产生的。复合词具有很强的组合能力、聚合能力和语义干涉造词能力。它不但以其巨大的能产性弥补了造词史上的不足,而且完全满足了现在和将来的造词需求。     

基于外部性的生态隐性脆弱地区生态与经济协调发展分析

研究指出,“生态隐性脆弱地区”是在“生态脆弱区”基础上提出的新概念,是指在生态脆弱区之外,受人类行为影响较多、暴露度高,存在或潜在生态系统失衡或退化风险的区域。生态隐性脆弱地区具有生态系统复合性、与人类行为相关大、对外界影响反应较缓慢三方面的主要特征。基于生态隐性脆弱地区的外部性分析,应从严格生态考核、严格外来投资审核、引进适用绿色技术、健全制度体系、完善生态补偿、强化理念更新六个方面推动生态隐性脆弱地区生态与经济协调发展。     

基于应力强度干涉模型的疲劳损伤研究

基于Miner法则,分析了工程上常用的阶梯谱级数对疲劳寿命精度的影响．建立了变换的JS-N曲线与阶梯谱拟合曲线的应力强度干涉数学模型,采用参数求解的数值解析法得到参数,并推导出了疲劳损伤的积分公式．对铁路货车转向架侧架运行36万公里（一个段修期）内分阶段的多次载荷谱测试数据进行分析,得出随着各阶段阶梯谱离散级数的增大,损伤成收敛趋势,寿命预测精度高．采用本文的分析方法,建立了侧架一个段修期的载荷谱概率模型,预测了侧架的寿命及其可靠性．     

政府干预经济行为法治化之探究

实现政府干预经济行为法治化是我国权力经济向法治经济转变的关键所在。政府干预经济行为法治化主要包括干预权力、程序及责任的法治化。推进政府干预行为法治化对于规范权力行使、提高干预绩效和保护市场主体权利意义甚大。当前,我国政府干预行为存在权力界限不清、权力滥用与腐败等突出问题。推进政府干预经济行为法治化是破解上述问题的重要路径。为此,我国应采取合理划定干预行为法律界限、严格干预经济行为程序规制、健全干预经济行为立法、落实干预经济行为法律责任及构建干预经济行为绩效评价法律制度等针对性措施,推进政府干预经济行为法治化发展。     

大学生心理危机干预的理论探源和策略研究

近年来,大学生心理危机事件屡见不鲜,对他们的生活、学习带来了较大的冲击和影响。大学生心理健康与否,不仅仅是大学生的个人问题,同时也是一个重要的社会问题。心理危机干预的理论模式主要包括认知模式、哀伤辅导模式、平衡模式、支持和干预技术模式、心理社会转变模式、教育、支持与训练的社会资源工程模式以及整合的干预模式等;大学生心理危机的类型主要表现为焦虑危机、哀伤危机、失恋危机和自杀危机;大学生心理危机干预的策略主要包括建立心理危机信息反馈系统、构建心理危机预防体系和改善大学生的社会心理环境。     

论母语对第二语言习得的影响

母语是影响二语习得最重要的因素之一。二语习得领域的研究者针对母语与第二语言习得之间的关系进行了深入研究,并提出了诸多理论学说。基于已往的研究成果,本文拟运用语言迁移理论对此问题进行较全面的论述,旨在探讨母语对二语习得的影响,构建克服母语干扰的理论框架。     

对短道速度滑冰比赛中“犯规干扰”的调查与分析

“犯规干扰”是短道速度滑冰运动员在竞赛中以犯规行为造成的对其他运动员在技术或战术方面的一种影响和破坏,以不同程度地干扰其他运动员水平的发挥,严重时会导致竞争的失败或出现伤害事故。其中以横切、碰撞、推人等性质造成的干扰最严重,外侧滑行受干扰率最多。基于此研究,为短道速滑运动队提供直接、有效地运动实践的指导。     

MIMO系统中利用空间相关性的同信道干扰消除算法

针对不适合进行波束赋型的MIMO系统中接收端如何消除同信道干扰的问题,提出了一种利用系统中干扰源的空间相关性进行同信道干扰消除的算法,并给出了估计空间相关性的最大似然算法。仿真结果表明,在2×2的Alamouti分集方案中,该算法相比于将干扰当作高斯白噪的方法在BER为10?2时可以获得3dB的增益;在2×4的分层空时复用方案中,该算法在存在一个强干扰源的情况下优势明显。     

基带升余弦谱波形的数字实现及其分析

介绍了二进制横向滤波器(BTF)直接实现数据限带传输升余弦谱脉冲波形成形的方法。着重研究了影响横向滤波器结构的参数(每波特内取样数 K,单位冲激响应波形旁瓣数 L)与BTF 的阻带衰减和所形成升余弦谱信号在最坏情况下的码间干扰之间的关系,为优化工程设计提供了依据。最后给出了数值实例和实验结果。