Benthic invertebrate assemblages and functional feeding groups in the Paraná River floodplain (Argentina)     

Florencia Lucila Zilli  Luciana Montalto  Mercedes Rosa Marchese 《Limnologica》2008,38(2):159-171

The benthic invertebrate assemblages and functional feeding groups in different mesohabitats of the Middle Paraná River–floodplain system were analyzed. Benthic invertebrates and bottom sediments were sampled in a secondary channel (center and bank mesohabitats), a temporal marginal fluvial wetland adjacent to the river, an isolated lake and a connected lake during low water level. Cluster analysis of average invertebrate densities based on the Bray Curtis dissimilarity index yielded a group composed by the mesohabitats with higher species richness, the floodplain lakes, banks mesohabitats and the wetland. The center mesohabitat of the main channel characterized by sandy sediments with low organic matter content and the lowest invertebrate densities and species richness was classified separately. Alpha diversity increased from the center mesohabitat (6 taxa) to the adjacent wetland (71 taxa), and were similar between the floodplain lakes (24 and 22 taxa) and the river bank mesohabitat (24 taxa). Gamma and beta diversities (Whittaker index) were 92 and 2.19, respectively. The highest turnover of taxa was between the river and the other mesohabitats and the lowest between floodplain lakes. Detrended correspondence analysis (DCA) showed a clear separation of wetland and banks from other mesohabitats (axis 1 and 2 explained 52.25% variance) explained by shredders and collector-filterers. The other mesohabitats were arranged in a gradient from the main channel mostly related to collector-gatherers to the connected lake and the isolated lake that were mostly characterized by predators and scrapers. The invertebrate assemblage complexity and functional feeding groups composition increased in the lateral dimension, from the center of the main channel to the temporal marginal fluvial wetland due to the influences of the spatial heterogeneity caused by different sources of organic matter inputs.  相似文献   

数值天气预报的新方法     

雷小途 《成都信息工程学院学报》1998,(2)

基于大气运动的连续性,构造了泛函。并直接利用测站的观测资料通过求该泛函的极小值,将数值天气预报从传统的在网格点上计算改为直接在测站上计算。  相似文献   

Changes in structural and functional diversity of nematode communities during a spring phytoplankton bloom in the southern North Sea     

Jan Vanaverbeke  Maaike Steyaert  Karline Soetaert  Vronique Rousseau  Dirk Van Gansbeke  Jean-Yves Parent  Magda Vincx 《Journal of Sea Research》2004,52(4):588

The response of nematode communities to the sedimentation of a spring phytoplankton bloom in a sandy, well-oxygenated sediment at a single station (station 330) in the Southern North Sea was investigated monthly from early March to July 1999. Both structural (nematode density, diversity, vertical distribution and community composition) and functional (feeding type distributions, number of species within feeding groups) characteristics showed considerable changes shortly after the arrival of fresh organic material at the sediment surface. The general increase in numerical densities and diversity was related to changes within the groups of selective deposit-feeding and epistrate-feeding nematodes. It is hypothesised that sedimentation and subsequent remineralisation of fresh organic matter during the spring phytoplankton bloom result in an increase of suitable food items (both living and dead). This, combined with the availability of oxygen, creates conditions in which many nematode species can co-exist.  相似文献   

Functional and biomechanic aspects of the scapular girdle and forelimbs of Unaysaurus tolentinoi (Saurischia: Sauropodomorpha)     

《Journal of South American Earth Sciences》2015

This study presents evidence about the biomechanics and forelimbs functionality of the basal sauropodomorph Unaysaurus tolentinoi (upper portion of the SM2 sequence, Santa Maria Supersequence, Upper Triassic from southern Brazil). Maximum and minimum motion angles were inferred in the joints, disregarding the presence and/or thickness of cartilage. Furthermore, processes and external structures of the bones were analyzed in attributing the functionality of forelimbs. Unaysaurus tolentinoi had well-developed grapple ability. However, the preserved elements and their osteological features are not conclusive about strictly bipedalism or quadrupedalism in U. tolentinoi.  相似文献   

Different levels of macroalgal sampling resolution for pollution assessment     

Isabel Díez  Alberto Santolaria  José María Gorostiaga 《Marine pollution bulletin》2010,60(10):1779-1789

The effects of using reduced sampling resolutions to study macroalgal vegetation patterns have not been studied sufficiently. Here, we test the influence of taxonomic resolution level, removal of occasional species, aggregation of species abundances into functional groups and data transformation in the detection of a long-term recovery process by phytobenthic intertidal assemblages. Results indicate that the aggregation of species data into the genus level has very little influence. Likewise, almost any significant information is lost when occasional algae are removed. Analyses at the level of families and orders still clearly detect differences between highly degraded and reference vegetation. By contrast, analyses based on class and functional group abundances capture quite different information. The effect of transformation is similar at the different taxonomic levels. Most surrogate measures properly reflect changes in diversity. It is concluded that genus level is the most appropriate surrogate approach for detecting the recovery process.  相似文献   

Importance of habitat structure as a determinant of the taxonomic and functional composition of lentic macroinvertebrate assemblages     

Ralf C.M. VerdonschotPiet F.M. Verdonschot 《Limnologica》2012,42(1):31-42

Variation in habitat structure provided by macrophytes is regarded as one of the determinants of macroinvertebrate species composition in lentic ecosystems, but mechanisms underlying this relationship appear to be confounded with site-specific factors, such as physicochemical factors, epiphyton and composition of the vegetation. To better understand the relationship between structural complexity of a macrophyte stand and its macroinvertebrate assemblage composition, it is essential to determine the ecological role of different components of habitat structure for the phytomacrofauna. Using artificial structures as macrophyte mimics, representing three growth forms (stems, broad-leaved, finely dissected) and three structure surface areas (0.1, 0.2, 0.3 m²), a full factorial field experiment was conducted in a series of drainage ditches. We investigated if macroinvertebrate assemblages colonizing the structures were affected by an increase in macrophyte structure surface area, structural complexity, or by a combination of both, and if the observed patterns were consistent among sites differing in physicochemical and habitat characteristics. Assemblages were characterized both in terms of taxonomic and functional composition, because we expected that non-taxonomic aggregation of species into functional categories would give a different insight in habitat complexity-macroinvertebrate relationships in comparison to approaches based on the taxonomic assemblage composition. Ditch intrinsic factors, in part reflected in the periphyton on the structures, explained the major proportion of the variance in both the taxonomical macroinvertebrate assemblages and functional groups among structures. Contrary to our expectation, patterns in the taxon-based and functional dataset resembled each other. Only a minor contribution of growth form to the explained variance was observed in the taxonomical dataset, whilst differences in functional composition were unrelated to habitat structure. In conclusion, processes operating on larger spatial scales overrode the micro-scale effects of habitat structural complexity and surface area on macroinvertebrates.  相似文献   

Stream macroinvertebrate communities change with grassland afforestation in central Argentina     

《Limnologica》2015

Lotic ecosystems are highly affected by land use changes such as afforestation of natural areas for management or commercial purposes. The aim of this study was to analyze the effect of pine plantations on benthic invertebrate communities in mountain grassland streams. Additionally, we assessed if the hydrological period modifies the effect of afforestation on stream invertebrates. Three headwater streams draining grasslands (reference streams) and three draining plantations of Pinus elliottii were selected in a mountain watershed of Córdoba province (Argentina). Hydrologic and physicochemical variables were registered and benthic invertebrate samples were collected in each stream at two different hydrological periods. Total invertebrate abundance, richness and diversity were reduced in afforested streams as well as the number of indicator taxa. In addition, invertebrate functional structure (i.e. taxonomic richness and total and relative abundance of functional feeding groups, FFG) showed differences between streams with different riparian vegetation and between hydrological periods. Total abundance of all FFGs was lower in afforested streams and scrapers’ relative abundance was higher in grassland streams at the low water period. In addition, in most FFGs richness was diminished in afforested streams. Changes in light intensity, hydrology and coarse organic matter inputs produced by afforestation alter fluvial habitats and consequently the composition and trophic structure of invertebrate communities in grassland streams of Córdoba mountains.  相似文献   

中国城市科教职能等级划分及空间分布研究   总被引：6，自引：0，他引：6  

王言荣  刘洁 《地理科学》2001,21(2):183-187

运用层次分析法和多指标加权求和方法得出中国城市科教职能综合评价指数，并用纳尔逊统计方法分析的结果作为科教职能等级划分的依据，把中国科教职能城市分为四个大级、六个亚级，据此分析得出中国科教中心城市的空间分布特征，无论从数量上还是从职能强度上都呈现出由东向西递减的趋势，且明显地偏集于环渤海区和华东区，针对其中存在的问题，提出了今后的发展对策；加快中西部地带科技和教育的发展，地方政府对中小型科教中心城市应给予政策倾斜和投入支持，以逐步缩小东西部的差距。  相似文献   

论广州名城传统中轴线   总被引：1，自引：0，他引：1  

杨宏烈  陈思访 《热带地理》2002,22(1):28-33

广州名城固有传统中轴线集直轴、曲轴、实轴、虚轴、路轴、绿轴、山水轴、文脉轴、网络坐标轴于一身 ,在城市自然地理与人文地理发展过程中不可他移。深刻认识其空间环境艺术、历史渊源、文化内涵 ,探讨其复兴、整治、拓展的规划手法 ,营造一个山水生态型的城市主题文化旅游集锦带 ,对切实保护名城、积极建设新区都具有重要的现实意义  相似文献   

Accounting seasonal nonstationarity in time series models for short-term ozone level forecast     

Sung Eun Kim  Ashok Kumar 《Stochastic Environmental Research and Risk Assessment (SERRA)》2005,19(4):241-248

Due to the nonlinear feature of a ozone process, regression based models such as the autoregressive models with an exogenous vector process (ARX) suffer from persistent diurnal behaviors in residuals that cause systematic over-predictions and under-predictions and fail to make accurate multi-step forecasts. In this article we present a simple class of the functional coefficient ARX (FARX) model which allows the regression coefficients to vary as a function of another variable. As a special case of the FARX model, we investigate the threshold ARX (TARX) model of Tong [Lecture notes in Statistics, Springer-Verlag, Berlin, 1983; Nonlinear time series: a dynamics system approach, Oxford University Press, Oxford, 1990] which separates the ARX model in terms of a variable called the threshold variable. In this study we use time of day as the threshold variable. The TARX model can be used directly for ozone forecasts; however, investigation of the estimated coefficients over the threshold regimes suggests polynomial coefficient functions in the FARX model. This provides a parsimonious model without deteriorating the forecast performance and successfully captures the diurnal nonstationarity in ozone data. A general linear F-test is used to test varying coefficients and the portmanteau tests, based on the autocorrelation and partial autocorrelation of fitted residuals, are used to test error autocorrelations. The proposed models were applied to a 2 year dataset of hourly ozone concentrations obtained in downtown Cincinnati, OH, USA. For the exogenous processes, outdoor temperature, wind speed, and wind direction were used. The results showed that both TARX and FARX models substantially improve one-day-ahead forecasts and remove the diurnal pattern in residuals for the cases considered.  相似文献