生态学试验设计与解释中的常见问题

一个"好"的试验,统计检验的显著差异可证明处理效应存在;而一个"坏"的试验,统计检验的显著差异本身并不能证明处理效应的真实存在.试验单位的不独立就可能使干扰因素偏倚地影响试验结果,是多种形式的伪重复的根本原因.如果不统筹地考虑试验方法和数据分析方法,环境要素的时空格局就可能被错误地当成处理效应.以案例分析的形式探讨了中国生态学试验设计与解释中常见的3个问题:(1)简单伪重复问题,这是Hurlbert[2]早已指出的伪重复情形中的一种,通常是把取样的重复当成了处理的重复;(2)把反复测量结果当成重复的问题,即对同一个对象的反应变量前后进行多次观测,却把这些观测值视为重复而进行统计检验所造成的问题;(3)混淆时空效应与处理效应的问题,由于取样方法(破坏性取样)或者研究对象(例如流动的水体)性质的特殊性等原因,数据中所体现出来的格局有可能由于时空效应而并非处理效应所造成.在这3种情况下,数据的产生方式与所用统计方法的前提相违背.     

利用正交试验优化建立大鼠条件恐惧记忆模型

目的 利用正交试验,优化建立大鼠条件恐惧记忆模型的最佳实验参数,寻找最佳试验条件。方法利用巴普洛夫条件恐惧原理,建立大鼠条件恐惧记忆模型;采用3因素3水平的正交试验设计,以模型建立24h后大鼠木僵反应时间为指标,观察不同参数条件下恐惧记忆的表达情况,确定最佳试验条件。以优选的实验条件建立条件恐惧记忆模型,并于24h、1周、2周、4周和8周后进行恐惧记忆保持检测。结果 直观分析结果表明,各因素影响能力依次为声音强度=循环次数>电击强度;方差分析结果表明,循环次数对实验结果有显著影响(P<0.05),声音强度和电击强度影响不显著(P>0.05)。确定最优实验条件为:声音75dB,电击0.8mA,循环15次。在模型建立24h和1周时,大鼠恐惧记忆保持良好,与对照组比较差异有显著性(P<0.001和P<0.05);第2周后恐惧记忆逐渐消退,与对照组比较差异无显著性(P>0.05)。结论 本实验明确了大鼠条件恐惧记忆模型影响因素的主次,优化了实验条件,为模型的标准化、规范化及后续研究提供了可借鉴的实验的依据。     

正交试验优化天麻超声波提取工艺的研究

为了优化天麻素的提取工艺,本研究采用超声法提取天麻素,以天麻素含量为指标,在单因素筛选基础上,采用正交试验优化提取工艺,选择料液比、提取次数和提取时间3个影响因素,每个因素3个水平进行正交试验。结果表明,最优提取工艺组合为:提取时间20min、料液比1∶15和提取次数2次;按照此工艺平行制备3批样品,天麻素的提取率为(0.339±0.13)%。     

转基因小麦“中间试验”与农艺性状评价

在湖北武汉对3个转基因小麦品系连续2次进行了"中间试验".结果表明在田间栽培条件下,转基因小麦植株个体生长发育正常,但转基因小麦主要农艺性状与对照间存在差异;特别是小区产量与本地小麦品种之间存在极显著差异;转基因小麦品系与其受体品系之间千粒重和小区产量上存在显著差异或极显著差异.组织化学和SDS-PAGE检测结果表明,外源基因能够稳定遗传,功能得到正确表达.     

材料性质和专业对解决四卡片问题影响的眼动研究

目的:探讨实验材料性质和专业背景等因素对四卡片推理问题解决的影响。方法:使用ASL-504眼动记录仪,以16名大学生为被试,采用2(材料性质)×2(专业)的二因素被试间设计。结果:材料性质主效应不显著,但材料性质在相对注视时间、相对注视次数和瞳孔直径上呈现显著差异;专业因素主效应显著,专业因素在平均注视时间和平均眼跳距离上差异显著,二因素交互作用不显著;"如果子句"和"那么子句"在所有眼动指标上不存在显著差异。结论:(1)抽象程度高的材料在理解四卡片问题时需要更多的加工,包括条件句及其组成部分;(2)不同专业背景对理解条件句有不同的影响;(3)条件句各组成部分在理解时得到同等重要的加工。     

材料性质和专业对解决四卡片问题影响的眼动研究

目的：探讨实验材料性质和专业背景等因素对四卡片推理问题解决的影响。方法：使用ASL-504眼动记录仪,以16名大学生为被试,采用2（材料性质）×2（专业）的二因素被试间设计。结果：材料性质主效应不显著,但材料性质在相对注视时间、相对注视次数和瞳孔直径上呈现显著差异;专业因素主效应显著,专业因素在平均注视时间和平均眼跳距离上差异显著,二因素交互作用不显著;＂如果子句＂和＂那么子句＂在所有眼动指标上不存在显著差异。结论：（1）抽象程度高的材料在理解四卡片问题时需要更多的加工,包括条件句及其组成部分;（2）不同专业背景对理解条件句有不同的影响;（3）条件句各组成部分在理解时得到同等重要的加工。     

湿润和干旱条件下喀斯特地区洼地表层土壤水分的空间变异性

在桂西北喀斯特洼地,用地统计学方法研究了旱季初期湿润和干旱条件下表层(0～5和5～10 cm)土壤水分的空间结构及其分布特征.结果表明,表层土壤水分存在明显的空间异质性和各向异性,呈现差异显著的斑块状分布格局.湿润条件下,土壤水分具有中等和较强的空间相关性,变程分别为33.15 m和15.75 m,其中0～5 cm层具有明显的趋势效应;干旱条件下,土壤水分则呈现出强烈的空间相关性,而且相似斑块的空间尺度有所减小,变程最小仅为8.22m;在平均含水量较低时(干旱条件)其变异程度较大,实际应用中应根据平均含水量水平采取不同的取样设计.实验区表层土壤水分空间变异及其分布格局的显著差异,主要是受地貌、平均含水量(降水)和地形等因素的影响.     

用正交试验法筛选樟芝菌适宜发酵培养基

用正交试验法对樟芝菌 (AntrodiacamphorataZang&Su)的发酵培养基进行了研究。选取马铃薯淀粉、葡萄糖、麦芽糖、酵母膏、蛋白胨、麸皮、KH2 PO4 、MgSO4 ·7H2 O等作为试验因素 ,采用L2 7(31. 3)正交表设计五因素、三水平的正交试验 ,对所选各因素的添加量分别作了试验 ,对菌丝干重和发酵液多糖含量结果作了方差分析 ,确定了合适的发酵培养基。试验结果表明 :樟芝菌的深层发酵适宜培养基是 :马铃薯淀粉 1 .0 0 % ,葡萄糖2. 0 0 % ,酵母膏 0 . 10 % ,蛋白胨 0 . 10 % ,麸皮 1 .0 0 % (或 0. 5 0 % ) ,KH2 PO4 0 . 10 % ,MgSO4 ·7H2 O 0 . 0 5 %。     

小鼠超数排卵优化试验方案研究

探讨建立一种适合贵州地区、高效、稳定的小鼠超数排卵优化方案。在饲养环境相同的基础上,对激素(PMSG, hCG)不同的剂量组合、注射间隔时间、小鼠周龄等影响因素进行了相关研究。试验结果表明:(1)平均采胚数量组间、平均异常胚组间与平均可用胚组间差异显著(p<0.05),注射10 IU的激素剂量组合获得受精卵最多,且异常胚最少,效果最佳。(2)第1、第2、第3组平均采胚数量组间差异显著(p<0.05),第1组与第2组平均可用胚组间差异不显著(p>0.05),但第1、2组与第3组差异显著(p<0.05),异常胚组间差异不显著(p>0.05),选择4周龄超排效果最佳。(3)第1、第2、第3组平均采胚数量、平均可用胚组间差异显著(p<0.05),平均异常胚组间差异不显著(p>0.05),PMSG,hCG间隔注射时间为48 h为最佳。     

基于正交试验法的景观水体叶绿素a 最佳提取条件研究

根据水体初级生产力测定常用方法中叶绿素a 测定法, 采用3 因素3 水平的正交法设计试验((L9(34)), 综合探究某喷泉水池景观水体测定过程中滤膜处理条件、浸提试剂和浸提温度等多因素多水平的共同作用下叶绿素a 提取效果的差异, 改进的正交试验设计规避了单因素控制变量实验的片面性。试验结果表明该喷泉池水的叶绿素a 含量较高,参考湖库景观水体富营养化分级标准已达到富营养化水平。提取过程中不同的正交试验组结果存在差异, 其中冷冻处理滤膜、丙酮乙醇混合溶剂、4 ℃条件下提取值最高, 为62.3 μg⋅L− 1。上述景观水体叶绿素a 提取条件组合(A2B3C1) 为正交试验最优水平组合, 采用正交试验的方法探究叶绿素a 提取最佳条件有利于对传统实验方法改进。     

Inter-and intraspecific effects of density manipulations upon females of two orb-weaving spiders (araneae: araneidae)

Summary A field experiment was conducted to establish whether or not inter-and intraspecific competition occurs between two syntopic species of orb-weaving spiders. Replicated single-species and mixed-species adult populations of the basilica spider, Mecynogea lemniscata, and the labyrinth spider, Metepeira labyrinthea, were established at a range of densities on open experimental units in the species' natural habitat. Each experimental unit was a 4mx1.6mx1m wood frame supporting branches upon which introduced spiders built webs. Survival and reproduction on the units were monitored from 1 August through 1 November 1978,There were no significant negative interspecific effects of density upon either survival or reproduction, which indicates that interspecific competition was not occurring during the experiment. There was statistically significant evidence of intraspecific competition between females for both species, but the negative density effects were small. They explained 5% of the variance in Mecynogea web height, 2% of the variance in Metepeira survival, and 1% of the variation in number of eggs per sac for Mecynogea.Hence inter-and intraspecific competition was either absent or weak in 1978, despite the fact that a field experiment conducted the previous year (Wise 1979) demonstrated that prey abundance was limiting the egg production of both species. Evidence of food limitation in 1977 followed by only weak competitive interactions the following year suggests that the significance of resource limitation and competition may vary temporally for the basilica and labyrinth spiders.     

零配比正交试验设计与结果分析

发现了正交配比试验的一种特殊情况-零配比正交试验,极差与平方和特征分析表明:常规正交(配比)试验极差与方差分析法均不能直接用于零配比正交试验结果分析．推导了3因素、3水平、无互作零配比正交试验极差估计与平方和分解校正方法,可有效提高试验结果分析的可靠性．     

Soil warming alters seed-bank responses across the geographic range of freshwater Taxodium distichum (Cupressaceae) swamps

? Premise of the Study: Climate warming is predicted to have far-reaching effects on the distribution of species, but those effects may depend on the flexibility of regenerating species in responding to climate gradients. We conducted a study to determine whether the variation in the response of seed banks to temperature varied across the latitudinal range of Taxodium distichum swamps in North America. ? Methods: The soil was collected in a long-term research network and heated experimentally to three current-day spring normal soil temperatures (average maximum daily spring normal soil temperatures during May in Illinois, Arkansas, and Louisiana, USA, respectively: 22°, 25°, and 29°C). A "normal" is the mean temperature calculated over a 30-yr interval (1971-2000). Seed-bank density and biomass responses were examined in relation to latitude and difference in the soil temperature of the experiment and the spring normal. ? Key Results: Using first- and second-order regression analysis, we determined that the variation in total germination density was lowest mid-range and in experimental soil temperatures similar to the spring normal. For some dominant species, the variance in germination density was higher in the northern (Cephalanthus occidentalis) or the southern part of the network (Saururus cernuus and Polygonum pensylvanicum). Overall, the variance of total biomass (root, shoot, whole plant) was higher if the experimental soil temperature was warmer than the spring normal. ? Conclusions: Our results suggest that the regeneration of some populations of swamp species may have more flexibility to respond to climate warming than others.     

Sampling errors in anchovy egg abundance estimates using the PAIROVET net

A replicate haul experiment was carried out using the verticallytowed PAIROVET net in an area of high abundance of anchovy eggsin the Bay of Biscay. The main aim of the experiment was tocompare the performance of ships of different size working inthe same area. In addition, we tested the performance of thePAIROVET net and the deployment methodology used to sample anchovyeggs for biomass assessment purposes. We concluded that underthe experimental conditions experienced in this cruise, differentships yield similar performances of the vertically towed PAIROVETnet if the methodology is kept similar. The ANOVA suggests thatthe systematic central sampling (SCS) scheme currently in usefor the Bay of Biscay anchovy biomass estimations (one stationout at 3 miles) adequately represents the surrounding area alongthe transect line. The among-station component of variance withinthe unit sampling area of the current SCS turned out to be comparableand, in some cases, smaller than the within-station variance.Consequently, the spatial design of the SCS adopted during routinesurveys appears to be a reliable strategy for sampling anchovyeggs in areas of high egg abundance, as in this experiment.In addition, it ensures fairly independent data units. In thearea of the experiment, the most disperse egg stages (like 2-and 3-day-old eggs) show a larger within-station component ofvariance than the spatial component of variance within the rectanglesof the current SCS. This suggests that for these stages, thesampling can still be improved cheaply by increasing the precisionof egg abundance estimates per station with larger sample sizes,without changing the spatial sampling scheme or the number ofstations. However, the benefits of this strategy will hardlyaffect the precision of the 1-day-old egg estimates becauseof their patchy distribution.     

Guidelines for the design and statistical analysis of experiments using laboratory animals

For ethical and economic reasons, it is important to design animal experiments well, to analyze the data correctly, and to use the minimum number of animals necessary to achieve the scientific objectives---but not so few as to miss biologically important effects or require unnecessary repetition of experiments. Investigators are urged to consult a statistician at the design stage and are reminded that no experiment should ever be started without a clear idea of how the resulting data are to be analyzed. These guidelines are provided to help biomedical research workers perform their experiments efficiently and analyze their results so that they can extract all useful information from the resulting data. Among the topics discussed are the varying purposes of experiments (e.g., exploratory vs. confirmatory); the experimental unit; the necessity of recording full experimental details (e.g., species, sex, age, microbiological status, strain and source of animals, and husbandry conditions); assigning experimental units to treatments using randomization; other aspects of the experiment (e.g., timing of measurements); using formal experimental designs (e.g., completely randomized and randomized block); estimating the size of the experiment using power and sample size calculations; screening raw data for obvious errors; using the t-test or analysis of variance for parametric analysis; and effective design of graphical data.     

Multigrid solution of the nonlinear Poisson-Boltzmann equation and calculation of titration curves.

Although knowledge of the pKa values and charge states of individual residues is critical to understanding the role of electrostatic effects in protein structure and function, calculating these quantities is challenging because of the sensitivity of these parameters to the position and distribution of charges. Values for many different proteins which agree well with experimental results have been obtained with modified Tanford-Kirkwood theory in which the protein is modeled as a sphere (reviewed in Ref. 1); however, convergence is more difficult to achieve with finite difference methods, in which the protein is mapped onto a grid and derivatives of the potential function are calculated as differences between the values of the function at grid points (reviewed in Ref. 6). Multigrid methods, in which the size of the grid is varied from fine to coarse in several cycles, decrease computational time, increase rates of convergence, and improve agreement with experiment. Both the accuracy and computational advantage of the multigrid approach increase with grid size, because the time required to achieve a solution increases slowly with grid size. We have implemented a multigrid procedure for solving the nonlinear Poisson-Boltzmann equation, and, using lysozyme as a test case, compared calculations for several crystal forms, different refinement procedures, and different charge assignment schemes. The root mean square difference between calculated and experimental pKa values for the crystal structure which yields best agreement with experiment (1LZT) is 1.1 pH units, with the differences in calculated and experimental pK values being less than 0.6 pH units for 16 out of 21 residues. The calculated titration curves of several residues are biphasic.     

Effects of an experimental increase in prey abundance upon the reproductive rates of two orb-weaving spider species (Araneae: Araneidae)

Summary A field experiment was performed to determine if food is a limited resource for adult females of two species of orb-weaving spiders, Mecynogea lemniscata and Metepeira labyrinthea. Spiders built webs after being added to open experimental units located in a mixed deciduous-pine forest in Maryland, USA. Each unit was a frame supporting dead branches of the type used by both species for anchoring webs. Spiders on half the units were exposed to natural prey densities only, while each spider on the other units was given laboratory-reared flies in order to increase prey availability above natural levels. Supplemental feeding continued for 2.5 months. At the end of the experiment all egg sacs were removed from the units.Providing additional prey did not increase the survival rate on the units (net effect of mortality, emigration and immigration). However, both species responded to additional prey by significantly increasing the number of eggs produced per female, indicating that food was a limited resource for these species. Median egg production per female increased from 34 to 62 for Mecynogea lemniscata and from 65 to 145 for Metepeira labyrinthea. Egg weight was not affected.Feeding rates and nearest neighbor distances were determined for spiders in non-experimental populations, which permitted evaluation of the experiment's naturalness. The effects of food supply upon the reproductive rates of the two species are discussed in relation to their numerical response and population dynamics.     

What’s in a site? Variation in lotic macroinvertebrate density and diversity in a spatially replicated experiment

Few studies have tested whether a small‐scale, experimental difference in biotic density and diversity detected at one site has any predictive capacity at other locations, nor whether such experimental differences are significant relative to overall spatial variation. In this study, we tested textural differences between substrata– previously shown to be critical to macroinvertebrate density and diversity at one site on the Steavenson River in southeastern Australia–and replicated the experiment at this site and at two others on the same river, plus at three sites on each of two other rivers (the Acheron and Little Rivers) in the same catchment. Nine rough and nine smooth colonization substrata were set out at each site on 19 December 1995, and at the start of the experiment (26 and 27 February 1996), invertebrates were hand‐picked from substrata while leaving epilithon intact. We re‐collected substrata after 28 days. Substrate texture had a consistent and strong effect upon species richness at all sites, except one, and was also associated with compositional differences at the family level. Textural effects on macroinvertebrate densities were present and varied among sites and rivers somewhat, but only three of nine common species showed significant interactions between textural effects and one of the two spatial scales, and these interactions explained <10% of variance. In most but not all cases, textural effects were the same as that previously observed–higher numbers on rough surfaces compared to smooth. Most variation in species richness and densities was explained by site, which accounted for 30% of variation in species richness, 60% of total numbers of individuals, and 9–75% of variation in abundances in all nine common taxa. Site differences were also associated with large shifts in faunal composition at the family level. Differences between rivers explained 0% of the variance in most cases but it was significant in explaining the abundance of one common species (the beetle Simsonia wilsoni), where it accounted for 59% of the variance. Our results indicate that a small‐scale effect, such as textural differences between substrata, can produce a consistent effect on measures of community structure and have some predictive capacity at other locations. However, the large differences between sites, relative to those seen between whole rivers, suggest that efforts must be directed to discovering what factors cause such localized fluctuations. Sites cannot be reasonably used as ‘representative’ of larger spatial units, such as long sections of entire rivers. Additionally, rivers may not necessarily have signature variation that always overrides localized, site‐based differences.     

Evidence of genetic and maternal effects on secondary sex ratio in cattle

There is a paucity of estimates of genetic variation for secondary sex ratio (i.e., sex ratio at birth) in dairy cattle. The objective of this study was to estimate the direct and maternal genetic variance as well as maternal permanent environmental variance for offspring sex in dairy herds. The data consisted of 77,508 births from 61,963 dams and 2,859 sires in 1,369 Irish dairy herds across the years 2003 to 2008, inclusive. Mixed models were used to estimate all parameters. Significant genetic variation in sex ratio existed, with a heritability for secondary sex ratio estimated at 0.02; the genetic standard deviation was 0.07 percentage units. No maternal genetic effects on secondary sex ratio were identified but the proportion of phenotypic variance in secondary sex ratio attributable to maternal permanent environmental effects was similar to that attributable to the additive genetic variance (i.e., 0.02). These results, therefore, suggest that the paternal (genetic) influence on secondary sex ratio is just as large as the maternal (non-genetic) influence, both of which are biologically substantial. The results from this study will be useful in generating a sample population of divergent animals for inclusion in a controlled experiment to elucidate the physiological mechanism underpinning differences in secondary sex ratio.