Biological effects of salinity gradient reversals in a southeast African estuarine lake

St Lucia Lake on the north coast of Natal, South Africa, has an area of 325 km² and is the largest estuarine complex in Africa. It consists of a 20 km tidal channel, averagingca. 400 m in width, linking the sea with the non-tidal lake which is H-shaped with a maximum length ofca. 40 km and width ofca. 20 km. Except during flood periods the depth of the lake does not exceed 2 m. The salinity gradient depends on evaporation, the configuration of the mouth and on the input of fresh water from four rivers which discharge into the northern and western areas of the lake. If fresh water input is high, the lake and much of the channel may be fresh. An intermediate stage features a normal salinity gradient while a third stage shows a reversed salinity gradient with salinities in excess of 100‰ in the upper reaches of the system. Changing salinities have marked effects on the biota. Aquatic macrophytes show cycles of appearance and disappearance depending on salinity tolerance and the presence of dormant stages. The resident benthic faunal species go through cycles of range expansion and contraction depending on prevailing salinities and recolonisation by dispersal phases. To date salinities in the southern part of the lake have approached, but not exceeded, lethal levels and this has therefore acted as a reservoir area. Catchment degradation and water abstraction are anticipated to exacerbate future salinity extremes. This has resulted in concern for the long term viability of this Ramsar site which has major southern African populations of hippopotamus and crocodile, provides breeding sites for South African Red Data water bird species and plays an important nursery role for marine fish and penaeid prawns.     

Food-web studies in shallow eutrophic lakes by the Netherlands Institute of Ecology: Main results,knowledge gaps and new perspectives

For more than 20 years scientists of the ‘Food-chain studies’ Group of the former Limnological Institute have been studying interactions within the pelagic food web. Purpose of research was to explain the structure and dynamics of the zooplankton and fish communities in lakes and reservoirs in relation to biotic and abiotic environmental factors. A so-called multi-species approach was used, in which all common and abundant species within a specific ecosystem were studied on the individual and population level with the same degree of detail. The recent results and the scientific approach used are evaluated and the main gaps in knowledge about food-web dynamics in shallow eutrophic lakes are identified and discussed. It is concluded that instead of the purely functional approach used so far, future studies should also include evolutionary aspects which determine the success of an organism in a given environment and that more attention should be paid to central questions in ‘community ecology’. This paper is based on a lecture given by the first author for the Netherlands Society of Aquatic Ecology on May 12th, 1992, in Amsterdam, The Netherlands.     

Developmental requirements for the ecdysoneless (ecd) locus in Drosophila melanogaster

The ecdysoneless locus in Drosophila melanogaster has been defined previously by a single conditional mutation, I(3)ecd¹, that causes an ecdysteroid deficit and larval death at the restrictive temperature, 29°C, although the primary role of the mutation in developmental processes has been unclear. Gene dosage and complementation studies reported here for ecd¹ and five nonconditional lethal alleles indicate that the ecd locus plays prezygotic and postzygotic roles essential for normal embryonic development, the successful completion of each larval molt, adult eclosion, and female fertility. The ecd locus is also required for normal macrochaete differentiation. For each observed phenotype, the severity of mutational effects was correlated with ecd mutant genotypes. In all cases, ecd¹ homozygotes were least affected. Mutants heteroallelic for ecd¹ and any one of four nonconditional recessive mutations were more severely affected than ecd¹ homozy-gotes, revealing these as hypomorphic alleles. For all phenotypic effects, mutants heteroallelic for ecd¹ and a dominant mutation (ecd^3D) were most severely affected. These individuals died during embryogenesis at 29°C and developed no macrochaetes on the dorsal thorax when transferred to 29°C during the white prepupal stage. The ecd^3D mutation also caused female semisterility in heterozygotes. Ecdysteroid regulation has been implicated previously in all the developmental processes disrupted by these ecd mutations except for macrochaete differentiation. © 1993 Wiley-Liss, Inc.     

生态系统稳态转换检测研究进展

在气候变化、人类活动等影响下,生态系统结构和功能可能发生大规模的突变,导致生态系统从一个相对稳定的状态进入另一个稳定状态,这种现象称为稳态转换。由于生态系统的复杂性,准确刻画生态系统多稳态并界定其临界点尚存在挑战,提升对生态系统稳态转换的检测和预测能力依旧是生态学领域研究的热点和难题。基于多稳态理论和稳态转换经典概念框架,阐释了稳态转换检测的理论基础;归纳总结出四种稳态转换检测方法的原理和优劣势;鉴于稳态转换的尺度依赖性,梳理了单一生态系统、区域综合生态系统和全球生态系统不同尺度下的稳态转换检测方法、研究思路和应用案例。基于研究进展和问题现状,提出在未来研究中,亟待发展适应复杂系统的综合检测方法;创新稳态转换多尺度分析的技术方法体系;深化生态系统稳态转换驱动机制研究,构建多元耦合机理模型;进而深化稳态转换检测结果链接生态系统管理的实践研究;解析生态系统服务和可持续发展机制。     

1985—2015年中国不同生态系统NDVI时空变化及其对气候因子的响应

植被是陆地生态系统不可或缺的部分,气候是影响其动态变化的重要驱动因素。因此,探究植被的时空变化及其与气候因子的响应关系,有助于理解陆地生态系统的内在演化机制。目前,不同生态系统尺度下的植被动态变化与气候因子的时间响应关系仍未被完整剖析。因此,为了厘清过去30年不同生态系统植被生长对气候因子的响应关系,利用GIMMS NDVI3g数据和气候资料数据,通过Theil-Sen Median趋势分析和Mann-Kendall检验分析了1985—2015年中国陆地NDVI的时空变化特征,结合时间序列相关分析探究了NDVI变化与降水、温度和饱和水汽压差的内部关联,探讨了中国不同生态系统植被与气候因子间的时间响应机制。结果表明：(1) 1985—2015年中国陆地植被呈现改善趋势,年均NDVI先减小后增加,拐点时间在1995年左右,整体变化率为0.5×10^-3/a。农田、森林和草地生态系统的植被显著改善的程度最高,湿地生态系统的植被退化趋势最显著。(2)中国陆地植被NDVI与气候因子的相关性存在明显的空间异质性,且受不同生态系统分区影响。内蒙古高原中部草地生态系统NDVI与降水...     

Enantioselective lipase-catalyzed ester hydrolysis: Effects on rates and enantioselectivity from a variation of the ester structure

In order to make a preliminary study of substituent effects on the rate and enantioselectivity obtained in esterolytic reactions catalyzed by a lipase from Candida rugosa, a series of racemic esters, derived from some α-alkyl and α-halo phenylacetic acids, were prepared. The reactions were studied at pH 6.0 and 50°C under which conditions uncatalyzed hydrolysis was relatively slow. Reaction samples were studied at different points of time by means of analytical chiral reversed-phase liquid chromatography, which permitted the simultaneous determination of product enantiomeric excess and of the degree of total ester hydrolysis. These data were then used to calculate initial rates as well as enantioselectivity. An increase of the steric bulk of the α-substituent was found to highly decrease the rate of the reaction. On the other hand, rates were higher for the p-nitrophenyl esters than for the corresponding 2-chloroethyl esters. Consistently, the enantioselectivity was found to be higher for the latter type of ester. The esters of the α-halo (bromo and chloro) phenylacetic acids gave mandelic acid as the final product. This was caused by a rapid solvolysis of the α-halo phenylacetic acid initially formed. © 1993 Wiley-Liss, Inc.     

Primary structure effects on peptide group hydrogen exchange

The rate of exchange of peptide group NH hydrogens with the hydrogens of aqueous solvent is sensitive to neighboring side chains. To evaluate the effects of protein side chains, all 20 naturally occurring amino acids were studied using dipeptide models. Both inductive and steric blocking effects are apparent. The additivity of nearest-neighbor blocking and inductive effects was tested in oligo-and polypeptides and, suprisingly, confirmed. Reference rates for alanine-containing peptides were determined and effects of temperature considered. These results provide the information necessary to evaluate measured protein NH to ND exchange rates by comparing them with rates to be expected for the same amino acid sequence is unstructured aligo- and polypeptides. The application of this approach to protein studies is discussed. © 1993 Wiley-Liss, Inc.     

Model misspecification and bias for inverse probability weighting estimators of average causal effects

Commonly used semiparametric estimators of causal effects specify parametric models for the propensity score (PS) and the conditional outcome. An example is an augmented inverse probability weighting (IPW) estimator, frequently referred to as a doubly robust estimator, because it is consistent if at least one of the two models is correctly specified. However, in many observational studies, the role of the parametric models is often not to provide a representation of the data-generating process but rather to facilitate the adjustment for confounding, making the assumption of at least one true model unlikely to hold. In this paper, we propose a crude analytical approach to study the large-sample bias of estimators when the models are assumed to be approximations of the data-generating process, namely, when all models are misspecified. We apply our approach to three prototypical estimators of the average causal effect, two IPW estimators, using a misspecified PS model, and an augmented IPW (AIPW) estimator, using misspecified models for the outcome regression (OR) and the PS. For the two IPW estimators, we show that normalization, in addition to having a smaller variance, also offers some protection against bias due to model misspecification. To analyze the question of when the use of two misspecified models is better than one we derive necessary and sufficient conditions for when the AIPW estimator has a smaller bias than a simple IPW estimator and when it has a smaller bias than an IPW estimator with normalized weights. If the misspecification of the outcome model is moderate, the comparisons of the biases of the IPW and AIPW estimators show that the AIPW estimator has a smaller bias than the IPW estimators. However, all biases include a scaling with the PS-model error and we suggest caution in modeling the PS whenever such a model is involved. For numerical and finite sample illustrations, we include three simulation studies and corresponding approximations of the large-sample biases. In a dataset from the National Health and Nutrition Examination Survey, we estimate the effect of smoking on blood lead levels.     

人为噪声对动物的非听觉影响

噪声在环境中广泛存在,城市化的迅速发展也使野生动物接触到人为噪声的机会增大。越来越多的证据表明,人为噪声在许多方面影响着人类的健康以及野生动物的生存。对这些研究进行总结发现,噪声会改变动物的生理状态,使其处在较高的应激水平,进而影响动物的抗氧化能力和免疫能力,甚至使雏鸟的端粒缩短。人为噪声的存在还会影响动物的学习和认知能力,干扰动物觅食、交流等行为。这些因素累积就可能会降低动物后代的存活率,改变物种丰度,对动物的生存造成威胁。对人为噪声带来的非听觉影响的研究,有助于更全面地了解噪声的潜在危害,采取更为积极的缓解应对措施。     

GENETIC AND SOCIAL INHERITANCE OF BODY AND EGG SIZE IN THE BARNACLE GOOSE (BRANTA LEUCOPSIS)

We present heritability estimates for final size of body traits and egg size as well as phenotypic and genetic correlations between body and egg traits in a recently established population of the barnacle goose (Branta leucopsis) in the Baltic area. Body traits as well as egg size were heritable and, hence, could respond evolutionarily to phenotypic selection. Genetic correlations between body size traits were significantly positive and of similar magnitude or higher than the corresponding phenotypic correlations. Heritability estimates for tarsus length obtained from full-sib analyses were higher than those obtained from midoffspring-midparent regressions, and this indicates common environment effects on siblings. Heritabilities for tarsus length obtained from midoffspring-mother regressions were significantly higher than estimates from midoffspring-father regressions. The results suggest that this discrepancy is not caused by maternal effects through egg size, nor by extra-pair fertilizations, but by a socially inherited foraging site fidelity in females.