Individual variability of diel vertical migrations in European vendace (Coregonus albula) explored by stationary vertical hydroacoustics

Abstract –  Diel vertical migration (DVM) is a widespread behavioural pattern in populations of aquatic animals. Its adaptive value is explained by a trade-off between the protection against visually feeding predators in the dark hypolimnion during daytime, and a higher food uptake in the upper food-rich layers during the night. Whereas vertical migration patterns of entire populations have been frequently described, less is known with respect to individual variability of DVM within fish populations. Here, individual migration patterns of European vendace ( Coregonus albula ) are described, obtained by stationary vertical hydroacoustics in Lake Stechlin (Germany) during the dusk and dawn phases of 2 months in 2004. The variability of speeds of depth change was high, with only a few fish rising or falling faster than 1 cm s⁻¹. Swimming activity was not dependent on fish size. There was some evidence that variability of echo strengths was highest in those fish which showed the greatest three-dimensional swimming distances which might indicate a limited swimbladder compensation during vertical migrations. However, migration seems to be performed mainly in a saltatory mode with vertical swimming always interrupted by phases of constant depth. It is suggested that these phases are used for pressure compensation by fish with the consequence that overall the frequency distribution of target strengths deviates only slightly between the start and the end of the recordings. Stationary hydroacoustics proved to be a useful tool for studying individual fish swimming behaviour.     

高山嵩草—苔草草地的植被演替

本文以生态位理论为指导,就广泛分布于青藏高原的嵩草—苔草草地在放牧条件下演替的过程和机理进行了研究,结果表明这类草地在放牧条件下演替有四个阶段:珠芽蓼+线叶嵩草—苔草群落(Ⅰ);线叶嵩草+苔草—垂穗鹅观草群落(Ⅱ);线叶嵩草+苔草—毛茛+甘肃马先蒿群落(Ⅲ);苔草+多茎委陵菜—毛茛+钝叶银莲花群落(Ⅳ);其衰退序列是Ⅰ→Ⅱ→Ⅲ→Ⅳ。封育可使群落中优良牧草的生态体积增大,使草地向进展方向演替。     

Typology in Mediterranean transitional waters: new challenges and perspectives

• 1. Transitional waters are ecotones between terrestrial, freshwater and marine ecosystems, being characterized by high spatial heterogeneity and temporal variability.
• 2. The EU Water Framework Directive (WFD) posed to the scientific community the challenge to classify these ecosystems into a small number of types, while retaining a functional classification of ecosystem types.
• 3. A niche theory approach is proposed to identify the limiting forcing factors organizing biological quality elements, i.e. the limiting niche dimensions.
• 4. The analysis of a macro‐invertebrate dataset from published papers on 36 Italian lagoons suggested a two‐level typological classification of Mediterranean lagoons.
• 5. Basic ecological theories, such as niche and island biogeography theories, have fundamental implications for the process of developing a typological classification for all aquatic ecosystems, as required by the WFD.

Copyright © 2006 John Wiley & Sons, Ltd.     

奇台荒漠草地自然保护区主要植物种生态位特征研究

采用Levins公式和王刚生态位计测方法,分析了奇台荒漠草地自然保护区16种植物在土壤pH值,土壤总盐含量和土壤有机质维上的生态位宽度和生态位重叠.结果表明,按照各资源维上生态位宽度的平均值大小可以把16种植物分成3类,第一类群的物种是该荒漠区植物群落中的建群种,对荒漠环境有很好的适应性,包括白梭梭(0.421)、沙拐枣(0.458)、角果藜(0.641)、琵琶柴(0.569)等;第二类群的物种对环境的适应能力较弱,物种有沙蓬(0.326)、对节刺(0.304)、旱麦草(0.221);第三类群的对沙漠的适应能力较弱,生态位平均值均小于0.2,包括盐穗木、梭梭、猪毛菜、假木贼和驼绒藜。优势种的生态位宽度越大相应的生态位重叠值也越大,存在一定的线性关系,表明优势种在对荒漠的环境适应上都趋于相似性。     

贵州喀斯特区野生葛藤群落主要种群生态位

通过对喀斯特区葛藤Pueraria lobata群落野外样地调查,分析其组成类型中16个优势种的生态位宽度、生态位相似性比例及生态位重叠.结果表明:①生态位宽度排在前6位的分别是葛藤,香叶树Lindera communis,竹叶椒Zanthoxylum planispinum,异叶鼠李Rhamnus heterophylla,粉枝莓Rubus bifioru,火棘Pyracantha fortuneana;②葛藤在喀斯特石漠化生境中的适应能力较强;③各种对的生态位相似比例为0～1不等,物种利用资源的相似程度差异较大;④16个种群间并未表现出显著的生态位完全重叠,各种群间利用资源的差异性显著,表明种群对资源的共享趋势并不明显,显示葛藤群落不稳定;⑤群落主要树种生态位重叠基本上是种群的生态位宽度越大,与其他种群的生态位重叠的机会越大,反之则越小.但在本研究发现,具有较大生态位宽度种群之间的生态位重叠值未必高.在喀斯特石漠化区,发展葛藤做饲料具有较大前景,但必须加大刈割等人工干扰措施,方能可持续发展.     

灵空山辽东栎林种群生态位特征

利用样地调查数据,以物种重要值作为资源状态指标,应用Levins,Hurlbert生态位宽度公式和Levins生态位重叠公式对山西灵空山林区辽东栎Quercus liaotungensis群落6种乔木、8种灌木和11种草本进行了生态位宽度和生态位重叠计算.结果表明:灵空山林区乔木树种以辽东栎(Levins生态位宽度Bi=1.1590,Hurlbert生态位宽度Ba=0.7960),油松Pinus tabulaeformis (Bi=0.990 7,B1a=0.536 1)的生态位宽度值较大;灌木树种以三裂绣线菊Spireae trilobata(Bi=1.095 0,Ba=0.509 0)的生态位宽度值较大;而草本层中,披针薹草Carex lanceolata的生态位宽度值最大(Bi=1.309 7,Ba=0.948 5).乔木、灌木、草本层各种群之间均有不同程度的重叠,重叠指数依乔木、灌木、草本层逐渐减少,总的表现为生态位宽度较大的物种对资源利用能力较强,与其他种群间的生态位重叠一般较大.     

基于实时性的图像插值加速算法研究

插值算法在图像处理中扮演着重要角色,本文介绍了双线性播值的原理,分析了浮点运算对算法效率的制约,提出了通过把像素值放大一定倍数转换浮点运算为移位运算的算法加速方案,重点设计了插值加速算法,然后对加速算法的运行效率和图像质量进行了对比测试,证实了加速算法在保证图像质量的基础上提高了插值效率,可以在实时系统中广泛应用.     

四川农业大学雅安校区鸟类群落结构分析

2009年11月至2010年11月,采用样线法对四川农业大学(雅安校区)的鸟类群落多样性进行了调查,共记录鸟类67种,隶属11目35科,在群落组成上雀形目鸟类占73.13%,在居留型上留鸟占64.18%。鸟类多样性夏季高于冬季,且在不同生境间变化明显,水体及周边区域相对较高。另外,通过对[树]麻雀(Passer montanus)等10种校园优势种生态位宽度及生态位重叠指数的测算发现,[树]麻雀、白鹡鸰(Motacilla alba)、白鹭(Egrettagarzetta)具有最大的生态位宽度,大山雀(Parus major)、红头[长尾]山雀(Aegithalos concinnus)、白头鹎(Pycnon-otus sinensis)之间生态位重叠最为明显。     

Quantifying landscape linkages among giant panda subpopulations in regional scale conservation

Understanding habitat requirements and identifying landscape linkages are essential for the survival of isolated populations of endangered species. Currently, some of the giant panda populations are isolated, which threatens their long-term survival, particularly in the Xiaoxiangling mountains. In the present study, we quantified niche requirements and then identified potential linkages of giant panda subpopulations in the most isolated region, using ecological niche factor analysis and a least-cost path model. Giant pandas preferred habitat with conifer forest and gentle slopes (>20 to ≤30°). Based on spatial distribution of suitable habitat, linkages were identified for the Yele subpopulation to 4 other subpopulations (Liziping, Matou, Xinmin and Wanba). Their lengths ranged from 15 to 54 km. The accumulated cost ranged from 693 to 3166 and conifer forest covered over 31%. However, a variety of features (e.g. major roads, human settlements and large unforested areas) might act as barriers along the linkages for giant panda dispersal. Our analysis quantified giant panda subpopulation connectivity to ensure long-term survival.     

Involvement of Cylindrocarpon destructans in root death of Pinus sylvestris seedlings: Pathogenic behaviour and predisposing factors

The common rhizospheric fungus Cylindrocarpon destructans was investigated in relation to its role in root death of Pinus sylvestris in Nordic nurseries and plantations. Laboratory methods were developed for studying similar root problems as well as the early effects of phytotoxicity and fungal infection. Seedlings grown under standardized optimal conditions were exposed to controlled stress (known to occur in nurseries), with or without C. destructans in the rhizosphere. Low light conditions, anaerobic root environment, and fungicide treatment were each found to predispose pine seedlings to invasion by the pathogen. The pathogen was very sensitive to competition as well as antagonism on the root, and fungicide‐induced inhibition of antagonists such as Trichoderma spp. also increased the severity of attack by the pathogen. To compete successfully, the pathogen would have to invade and dominate weakened roots prior to the arrival of saprophytes. Toxic metabolites produced by the pathogen weakened or killed nearby root tissues, and pathogen metabolites seemed to prevent saprophytes from taking hold in the infected roots. Such heavily infected, dead roots may act as inoculum sources allowing the pathogen to invade adjacent living roots, even healthy ones. Dead roots left in nursery soil after earlier harvests may act as reservoirs of inoculum for long periods and pose a threat to new plants.