Changes in the density and growth of brown trout (Salmo trutta) after intensive removal of sympatric Arctic charr (Salvelinus alpinus) in the sub‐Arctic lake Møkkelandsvatn,Norway

This study tests the basic hypothesis that the removal of charr, Salvelinus alpinus (L.), would cause an increase in both the growth and density of a sympatric trout population, Salmo trutta L. The charr population was characterised by slow‐growing individuals, with a high proportion of mature fish, that is typical for so‐called overpopulated populations. A total of 31,000 charr was removed from the lake in the period 1990–1992, and the density of younger trout (1+, 2+), but not older trout (3+, 4+), increased. The growth of older trout (3+, 4+) increased, but the evidence for similar growth increases of younger trout (1+, 2+) was limited. From 1989 to 1990, the proportion of trout increased from 30 to only 40% of the total catch, but from 1991 to 1994, it was significantly higher (60–80%) than that of charr. Total trout biomass increased to a maximum in 1992 and then decreased so that the biomass of 1994 was nearly similar to that of 1989, that is before the start of the charr removal. Back‐calculated lengths of trout from otoliths showed that 2+ and 3+ trout caught in the pelagic were growing consistently faster over previous years than those caught in the littoral, while this was not the case for the 4+ fish. Therefore, the hypothesis was partially supported; the growth rate of trout increased (age groups 1+ to 4+), while the density of juvenile trout (1+, 2+), but not the older trout (3+, 4+), increased after the removal of charr.     

胚胎冻融技术及其在我国肉羊产业中的应用

胚胎冻融技术可使胚胎移植不受时间、地点的限制，从而达到提高胚胎移植效率的目的，研究和优化胚胎冻融技术对胚胎移植工程的发展具有重要的意义。主要对胚胎冻融技术的原理、特点及其在肉羊产业中的应用情况进行了综述，旨在阐明胚胎冻融技术对我国肉羊产业发展的重要作用。     

Influences of population density,temperature and latitude on the growth of invasive topmouth gudgeon Pseudorasbora parva

Plasticity in life‐history traits provides advantages for introduced fish in overcoming demographic bottlenecks that would otherwise inhibit establishment. Here, the influence of population density, temperature and latitude was tested on the growth increments and growth rates of invasive populations of topmouth gudgeon Pseudorasbora parva, a small Asian cyprinid fish that is invasive across Europe. Aquaria experiments tested the roles of fish number and temperature on growth increments under a fixed food supply, pond experiments tested the role of density on growth increments, and a field study completed in England and Wales tested the influence of density and latitude on growth rates. In aquaria experiments, whilst growth increments were higher at 21 and 23 °C than at 19 and 25 °C, fish number had a greater influence on growth than temperature. Higher growth increments were produced at lower densities. In experimental ponds, growth increments were significantly higher in ponds with low densities of P. parva compared with those at elevated densities. In the field study comprising 10 wild populations across a latitudinal gradient of 4.0°N, a difference in mean air temperatures of approximately 3 °C, and estimated densities between 0.5 and 65.0 m^?2, population density was the only significant predictor of growth rates. Whilst populations at very low densities comprised of significantly faster growing individuals, there were no significant differences when densities were between 15 and 65 m^?2. Thus, invasive P. parva populations have considerable growth plasticity, especially at low densities, with this likely to be important in their ability to colonise new environments.     

氨氮胁迫对四鼻须鲤鱼肝脏GST酶活力的影响

实验采用生态毒理学方法,以NH4Cl为实验药物,设置0、50、150和250mg/L实验浓度。通过对野生和养殖群体的四鼻须鲤鱼氨氮对肝脏谷胱甘肽巯基转移酶（GST）活力的影响,比较两个群体抗氨氮能力。结果表明：在相同的氨氮浓度和胁迫时间下,四鼻须鲤鱼养殖群体GST酶活力的变化趋势与野生群体大致相同。除250mg/L浓度组在胁迫5d和10d时,野生群体酶活性略低于养殖群体外,在其余时间点的野生群体酶活性均高于养殖群体,而且,在高浓度氨氮胁迫下,野生群体肝脏的GST酶活性达到峰值的时间比养殖群体更短,显示出较强的抗氨氮能力。     

Factors Affecting Recipients' Pregnancy,Pregnancy Loss,and Foaling Rates in a Commercial Equine Embryo Transfer Program

During 11 breeding seasons, 351 7- to 10-day-old horse embryos were nonsurgically transferred into recipients that ovulated between 3 and 10 days earlier. Pregnancy rates at 14 and 40 days and foaling rates were 77.8% (273/351), 69.2% (243/351), and 64.4% (226/351), respectively. Pregnancy loss between 14 and 40 days was 11% and between 40 days and delivery was 7%. The transfer of quality grade 3 to 4 embryos resulted in a significantly lower pregnancy rate at 14 days compared with the transfer of grade 1 to 2 embryos (46.2% vs. 79%; P < .05). Eight-day-old embryos resulted in significantly lower pregnancy losses than day 9 or 10 embryos, as occurred for embryos between 400 and 1200 μm compared with embryos <400 μm. Embryos recovered from mares >20 years resulted in a significantly higher pregnancy loss rate than those recovered from younger mares. The same happened for embryos coming from mares affected by reproductive pathologies compared with healthy mares performing sport activity. None of the evaluated parameters influenced recipients' foaling rate significantly.     

轮回选择在烟草育种中的应用及方法

提出了在烟草育种中应用轮回选择方法的必要性,综述了轮回选择改良群体的理论与方法和轮回选择在烟草育种中的应用效果,同时探讨了轮回选择在烟草群体改良中的应用特点和方法。     

湘西北长果安息香种群数量与分布格局

对湖南石门壶瓶山景关门、桑植龙潭坪茅垭村样地的长果安息香(Changiostyrax raxdolichocarpa)种群数量和分布格局进行调查和分析。结果表明：长果安息香种群的年龄结构呈衰退型，个体数量主要集中在小树(IV龄段)，幼龄级株数和老龄级株数匮乏；长果安息香种群在进入生理死亡年龄前有2个死亡高峰，第1个峰值产生于幼树(II、III龄段)，主要原因是种内和种间竞争(主要是光照)，第2个峰值产生于中树长成大树阶段(V、VI龄段)，除种内、种间对环境的竞争外，生长地土层浅薄、大树倒伏及人为砍伐亦加剧了该峰值的产生；种群整体呈聚集分布类型，小树向中树、大树变化过程表现出聚集分布向随机分布转变，导致长果安息香濒危的主要原因是种子萌发率极低、种群竞争能力较差以及人为干扰等。     

金融监管信号传递与金融市场有效运行

金融市场是金融监管当局与金融市场参与者之间动态博弈、合作共生的信息不对称系统。通过把信号博弈和重复博弈思想引入金融监管理论研究，构建以金融市场有效运行为反馈信号的金融监管当局与金融市场参与者之间的监管信号传递模型，分析金融市场治理中有效监管信号的传递机制。结果表明：金融监管力度与金融市场有效运行水平之间存在分离、混同两种均衡关系；在金融监管声誉效应的驱动下，金融监管当局倾向于选择混同均衡策略，而不是分离均衡。因而只有建立通畅的金融监管信号传递及反馈机制，强化并放大金融监管信号显示，增大监管乘数效应，形成良性的监管声誉效应，才能保障金融市场的有效运行。     

Simulating farming practices within a region using a stochastic bio-decisional model: Application to irrigated maize in south-western France

Agricultural is a major contributor to environmental resource management problems. Modelling the distribution of agricultural land use to evaluate current situations or scenarios is an important issue for policy-makers and natural resource managers. A promising approach is the use of bio-decisional models based on decision rules. However, at the regional scale, the large number of farmers makes it difficult to identify decision rules, and the diversity of farmers' decisions is rarely considered. To this end, we developed SIMITKO, a spatialised and stochastic bio-decisional model, able to simulate the spatial and temporal variability in farming practices. We focused on the choice of varietal earliness and sowing practices of maize (Zea mays L.) in the Baïse sector (south-western France). Model development was based on statistical analyses of surveys of farmers’ practices to identify their current strategies, the best variables to describe the practices and the probabilities associated with the values of the variables for each strategy. We tested SIMITKO by simulating the dynamics of areas sown with maize. Comparing model predictions of practices to observed data showed generally good predictions of sowing dynamics but less satisfactory predictions of varietal earliness choices. Possible improvements are suggested.     

6种钝化剂对糙米镉含量及镉在水稻中的转移和富集的影响

旨在为合理使用钝化剂及水稻糙米镉(Cd)含量与Cd在水稻体内富集和转移的关系提供一定的理论依据。从6种钝化剂中筛选出能够抑制糙米Cd积累的材料,通过对不同超标程度水稻组的产量、糙米Cd含量、各个器官对Cd的富集系数和转移系数进行统计分析,探讨不同钝化剂对Cd在水稻体内转移和富集的影响。结果表明:与对照相比,低、中浓度C材料和FA材料能够降低糙米中Cd浓度;FB材料和中、高浓度FD材料会促使糙米中Cd的积累。水稻各器官对Cd富集能力,无超标水稻为根茎米叶糠,超标水稻为根茎米糠叶;Cd向糙米的转移途径中,在不超标水稻组中糠—米的转移能力最强,在超标水稻组中叶—米的转移能力最强。