变温下铃木氏果蝇年龄-阶段两性生命表研究

为进一步阐明温度对铃木氏果蝇生长发育和繁殖的影响,补充铃木氏果蝇基础生物学信息,本研究在室内14~20℃、26~32℃变温条件下人工饲养铃木氏果蝇,对比不同变温条件下铃木氏果蝇的发育历期、存活率和繁殖率,并构建年龄-阶段两性生命表。结果表明:与26~32℃处理相比,14~20℃变温处理下铃木氏果蝇的各阶段发育历期、成虫寿命及产卵前期均较长。14~20℃变温处理下该虫年龄-阶段特征存活率(sxj)、年龄-特征存活率(lx)、年龄-阶段特征生殖能力(vxy)以及期望寿命(exy)均高于26~32℃处理,而繁殖力(fxj、mx)低于26~32℃处理。14~20℃变温处理下该虫的内禀增长率(rm)和周限增长率(λ)低于26~32℃处理,而平均世代周期(T)和种群加倍时间(t)高于26~32℃处理。在变温条件下,高温相较于低温更利于铃木氏果蝇的种群增长。     

塑料大棚结构风振响应规律研究

为研究塑料大棚结构的风振响应规律,提出了塑料大棚结构风振响应分析的被研究块体方法,推导了塑料大棚骨架结构单元段的段间内力计算公式,设计了被研究块体构成方式,构建骨架结构中被研究块体的力学模型,给出了被研究块体方法实现过程;采用等截面圆柱杆的波动传播算例,验证了方法的有效性。在同时考虑平均风和脉动风作用、仅考虑脉动风作用、仅考虑平均风作用的3种工况下,针对不同跨度塑料大棚骨架结构的风振响应进行时程分析,得到骨架结构的节点位移和截面应力空间最大值的出现位置。结果表明:节点位移和截面应力均为脉动风荷载作用的计算结果明显大于平均风荷载作用的计算结果。因此,塑料大棚结构的风振响应分析需要考虑脉动风荷载的作用。     

Year class variation in fluctuating asymmetry in perch (Perca fluviatilis L.) from an acidic aluminium-rich lake

Fluctuating asymmetry is the random deviation from perfect bilateral symmetry owing to developmental perturbation, proposed as an indicator of sublethal environmental effects. This was measured in perch (Perca fluviatilis L.) from an acidic aluminium-rich lake. Eleven paired meristic and morphometric characters were scored for fluctuating asymmetry. Level of fluctuating asymmetry differed significantly between year classes for two of the meristic characters, lower extra gill rakers and upper extra gill rakers, and also for an index summarizing number of asymmetric meristic characters per individual. This year class variation in fluctuating asymmetry is probably due to large variation in water quality during early development of perch embryos in spring. For future work on fluctuating asymmetry on fish we recommend the use of as many year classes as possible in the analyses.     

Effect of temperature on EDTA‐extractable copper in soils

Abstract

Two contrasting soils were extracted with 0.05 M EDTA in 1 M CH₃ COONH₄ at pH 6, before and after incubation for 4 weeks at constant (10, 20 or 30°C) or fluctuating (10/30, mean 20°C) temperatures. Less copper was extracted from soils which were incubated at fluctuating temperature than from those maintained at a constant 20 C. Where incubation temperature was constant, extractable copper increased or decreased with increasing temperature depending on the soil and how it was treated. Recovery of added copper was low initially but increased during the incubation. Maximum recovery was associated with low incubation temperature in one soil, but high temperature in the other. The amounts of copper extracted were slightly increased by γ‐irradiation of the soils. Extractable copper was also increased by increasing the temperature at which the extraction was performed.     

Fluctuating resources, disturbance and plant strategies:diverse mechanisms underlying plant invasions

This paper examines the hypothesis that non-native plant invasions are related to fluctuating resource availability as proposed by Davis et al.(2000).I measured relative functional responses of both invasive and native plants to changed resource availability due to nutrient enrichment and rainfall,and to increased disturbance.Data are presented from studies in two contrasting ecosystems.First is a series of glasshouse and field experiments on the invader Hieracium lepidulum and associated invasive and native species in subalpine temperate New Zealand.Second is a field study of invasive and native plant responses to altered disturbance regimes and rainfall from tropical savannas of north eastern Australia.Invaders responded differently from native species to changes in resource availability in both subalpine and tropical studies.However,invaders differed among themselves showing that different species exploit different functional niches to invade their respective habitats.These findings contribute to the contention that the fluctuating resource hypothesis does not provide a universal explanation for plant invasions.The diverse functional responses to increased resource availability among invaders in this and previous studies suggest that the cause of invasion depends on unique combinations of habitat and functional attributes of invaders and native assemblages.Such findings imply that universal predictions of what will happen under climate change scenarios across the globe will be difficult to make.     

信息不对称引发的农产品市场交易问题及对策——基于农产品产业链视角

信息经济学认为,在现实市场交易中各主体拥有的信息是不对称的,信息不对称现象同样也存在于农产品交易市场中。基于农产品产业链视角,总结了3类突出的信息不对称现象,并分析了这些信息不对称引发的农产品市场交易问题,最后从市场自发机制和政府干预2个角度提出了相关对策。     

基于洛伦茨曲线的陕北黄土高原降雨分布不均匀性分析

利用建立的基尼系数降水分布不均匀性模型,对延安市和榆林市1961—2010年的降水量、基尼系数和洛伦茨不对称系数的系列进行研究,并用Mann—Kendall方法趋势分析和检验。研究结果表明,近50年来榆林市和延安市的年降水量呈下降趋势,年平均基尼系数分别为0.61和0.56;大于1的洛伦茨不对称系数的年份占总年份的比例分别约为33%和16.7%。榆林市的基尼系数呈上升趋势,洛伦茨不对称系数呈下降趋势;延安市的基尼系数呈下降趋势,洛伦茨不对称系数呈上升趋势。榆林市的降水分布不均性增强,主要是由于降水量小的月份所占的比例较大;延安市降水分布趋于均匀,降水量大的月份所占比例增加。榆林市在1972、1986年和1997年的洛伦茨不对称系数有较大波动,这些年中降水不均匀性主要是由于降水量大的月份引起的,同期也是土壤干旱异常的年份。因此,洛伦茨曲线从一种新的角度来量化评价降水分布时间不均匀性及其成因,为研究土壤干旱和水土流失等自然灾害成因机理提供科学依据。