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Frequent Species (frequent + species)
Selected AbstractsScale dependence of diversity measures in a leaf-litter ant assemblageECOGRAPHY, Issue 2 2004Maurice Leponce A reliable characterization of community diversity and composition, necessary to allow inter-site comparisons and to monitor changes, is especially difficult to reach in speciose invertebrate communities. Spatial components of the sampling design (sampling interval, extent and grain) as well as temporal variations of species density affect the measures of diversity (species richness S, Buzas and Gibson's evenness E and Shannon's heterogeneity H). Our aim was to document the small-scale spatial distribution of leaf litter ants in a subtropical dry forest of the Argentinian Chaco and analyze how the community characterization was best achieved with a minimal sampling effort. The work was based on the recent standardized protocol for collecting ants of the leaf litter ("A.L.L.": 20 samples at intervals of 10 m). To evaluate the consistency of the sampling method in time and space, the selected site was first subject to a preliminary transect, then submitted after a 9-month interval to an 8-fold oversampling campaign (160 samples at interval of 1.25 m). Leaf litter ants were extracted from elementary 1 m2 quadrats with Winkler apparatus. An increase in the number of samples collected increased S and decreased E but did not affect much H. The sampling interval and extent did not affect S and H beyond a distance of 10 m between samples. An increase of the sampling grain had a similar effect on S than a corresponding increase of the number of samples collected, but caused a proportionaly greater increase of H. The density of species m,2 varied twofold after a 9-month interval; the effect on S could only be partially corrected by rarefaction. The measure of species numerical dominance was little affected by the season. A single standardized A.L.L. transect with Winkler samples collected <45% of the species present in the assemblage. All frequent species were included but their relative frequency was not always representative. A log series distribution of species occurrences was oberved. Fisher's , and Shannon's H were the most appropriate diversity indexes. The former was useful to rarefy or abundify S and the latter was robust against sample size effects. Both parametric and Soberón and Llorente extrapolation methods outperformed non-parametric methods and yielded a fair estimate of total species richness along the transect, a minimum value of S for the habitat sampled. [source] Dispersal and life span spectra in plant communities: a key to safe site dynamics, species coexistence and conservationECOGRAPHY, Issue 2 2002Roel J. Strykstra Dispersal and life span of individual plant species within five plant communities were assessed to obtain a characterization of these communities in this respect. Such a characterization is important in the context of restoration and maintenance. The most frequent species of five communities were ranked in eight classes according to their level of seed dispersal capability, their seed bank formation (dispersal in time and space) and their individual life span. In the communities, all eight classes were found, but communities differed in the distribution of the species over the classes. A theoretical framework was constructed to use the level of specialization of plant species in terms of dispersal in space and time, and life span, to define the characteristics of safe site dynamics within communities. Following simple rules, the relative reliability of the occurrence of safe sites in space and time was defined. After that, the relative reliability of the habitat was linked to the best fitting combination of trait specialization level. Having defined this link, communities could be characterized in a comparative way by their level and pattern of reliability of the opportunities for recruitment in space and time. The meaning of the coexistence of a range of trait combinations in one community was discussed. It was postulated that habitat reliability can explain this by assuming that the habitat of the community is part of a larger system, or consists of several "subsystems". These insights need to be considered in nature conservation. Succession and also specializations beyond the scope of dispersal and life span may influence the occurrence of species in a seemingly unfit habitat (for instance the occurrence of semi parasitic annuals in a community of perennials, because they use the perennial root system of other species). Finally, the meaning of safe site reliability in space and time in the context of restoration of communities was discussed. The reliability in space and time may be different today from that of the past, which restricts the feasibility of restoration of communities. [source] Hemeroby, urbanity and ruderality: bioindicators of disturbance and human impactJOURNAL OF APPLIED ECOLOGY, Issue 5 2002M. O. Hill Summary 1Species vary according to whether they benefit from or are harmed by disturbance and intensive human activity. This variation can be quantified by indices of disturbance and unnaturalness. 2An urban flora was characterized by comparing quadrat data from cities with several large data sets from the countryside. Existing scales of species response to disturbance and unnaturalness, ruderality (a plant's ability to survive in disturbed conditions) and hemeroby (a measure of human impact) were contrasted with derived scales based on the number of associated annuals and aliens and with ,urbanity', defined as the proportion of urban land in the vicinity of each quadrat. 3Species presence data were available from 26 710 quadrats distributed through Great Britain, with urban sites only in central England. Satellite imagery was used to measure the proportion of urban land cover in the vicinity of each quadrat; 2595 quadrats were located in 1-km squares having at least 40% cover of urban land. 4The 20 species having highest urbanity were all alien to Britain, comprising 12 neophytes and eight archaeophytes. 5Of the 20 most frequent species in quadrats situated in 1-km squares with at least 40% urban land cover, 18 were natives. The two exceptions were Artemisia vulgaris , an archaeophyte, and Senecio squalidus , a neophyte. 6Both ruderal and hemerobic species, as usually defined, include many non-urban arable species. The hemeroby scale of Kowarik (1990 ), designed for Berlin, does not work well in Britain. 7The proportion of associated annuals (annuality) and the proportion of associated neophytes (alien richness or xenicity) can be developed into good indices. The annuality scale is very well defined because annuals tend to occur with other annuals. Plants with high annuality are mostly arable weeds. 8Urban specialists in central England are, with a few exceptions, character-species of the phytosociological classes Artemisietea , Galio-Urticetea and Stellarietea . Most of them have numerous non-urban associates and they do not form a very well defined group. They have intermediate levels of annuality combined with relatively high levels of xenicity. 9While it is possible to develop indices of hemeroby, urbanity and ruderality, these concepts are relatively complicated. Annuality and xenicity are simpler measures that can complement Ellenberg values, but definitive values for Great Britain would require additional data from southern England. [source] Biogeographical determinants of lichen species diversity on islets in the West-Estonian ArchipelagoJOURNAL OF VEGETATION SCIENCE, Issue 2 2006Inga Jüriado Abstract Questions: Do islet area, number of biotopes and distance from the mainland shape lichen species richness on islets? Are there any species- or substrate group-specific trends associated with these factors? Location: Islets of the west Estonian Archipelago, Estonia. Methods: A species list was compiled for each of the 32 islets and the relative abundance of each species was estimated. The lichens were divided into seven groups according to their substrate preferences. Generalized linear model (GLIM) analysis was applied to test the effect of the islet traits on the number of lichen species on the islets and in the substrate groups. The probability of presence/absence and abundance of the most frequent species according to the islet traits were tested with GLIM and general linear mixed model. Results: The lichen flora of the islets consisted of 326 taxa, the number of lichen species per islet varied from 2 to 197. Total number of species per islet and within the substrate groups was positively correlated with islet area and with number of biotopes, and negatively correlated with distance from the mainland; however, these relationships varied among the substrate groups. Although individual lichen species showed variation in responses, general trends in island biogeography were evident. Conclusions: The distribution pattern of lichens on the studied islets follows the theory of island biogeography: the number of species per islet depends on isolation, area and biotope diversity. Species specific traits, such as dispersal strategy and growth form, as well as availability of a particular substrate are important for formation of the lichen flora on islets. [source] Malassezia yeast species isolated from Iranian patients with pityriasis versicolor in a prospective studyMYCOSES, Issue 4 2010Abbas Rasi Summary The goal of this study was to determine the prevalence of Malassezia species in pityriasis versicolor lesions and to examine if the range of species varies with patients characteristics such as: age, sex and family history and also clinical findings such as site and number of the lesions. In a prospective study from July 2006 to July 2007, the patients with a clinical diagnosis of pityriasis versicolor (n = 166) were asked to participate in the study. A total of 116 patients had positive culture for Malassezia species: M. globosa was found in 52 (31.3%) cases, M. furfur in 34 (20.5%) cases, M. pachydermatis in 12 (7.2%) cases, M. restricta in 12 (7.2%) cases, M. slooffiae in 6 (3.6%) cases. According to our data, M. globosa is the main species causing pityriasis versicolor, M. furfur was found to be the second-most frequent species. M. sympodialis and M. obtusa were not found in any case, and in 30.2% of patient's Malassezia culture was negative. [source] Feasible identification of Staphylococcus,epidermidis using desferrioxamine and fosfomycin disks,APMIS, Issue 1 2008ANA LÚCIA SOUZA ANTUNES Coagulase-negative Staphylococcus spp. (CoNS) have emerged as predominant pathogens in hospital-acquired infections, as well as reservoirs of antimicrobial resistance, increasing the necessity of developing reliable methods for identification of the most frequent species. The aim of this study was to propose a simplified method for identification of Staphylococcus epidermidis. A total of 490 isolates of CoNS were identified by Bannerman's method. Taking into account distinct approaches for identification of S. epidermidis, among CoNS, we proposed the use of only two disks: desferrioxamine for the initial trial, and fosfomycin to match the final identification. Of the 320 isolates susceptible to desferrioxamine, Bannerman's method identified 238 S. epidermidis and 73 S. hominis, while we achieved identification of 239 S. epidermidis and 76 S. hominis. Compared to Bannerman's method, the method proposed here obtained a sensitivity of 99.5%, and had a positive predictor value of 99.2%. We also used a genotypic method for identification of S. epidermidis by polymerase chain reaction (PCR) targeting the tuf gene. In conclusion, the method proposed here has proved to be useful for the identification of S. epidermidis, the most frequent species of CoNS isolated from blood cultures in clinical microbiology laboratories. [source] Loss of Ostracoda biodiversity in Western Mediterranean wetlandsAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 3 2008José M. Poquet Abstract 1.The coastal area of Valencia (Spain) in the Western Mediterranean is rich in freshwater and brackish wetlands. These areas are mostly protected for bird conservation but are also highly affected by human impacts. Six shallow lakes located in Ramsar wetland sites of this area were studied in order to assess past and present ostracod biodiversity and relate it to the status of the lakes, taking into consideration the indicator value of these easily fossilizable crustaceans. 2.In all the wetlands studied, ostracod taphocoenoses showed much higher species richness than the corresponding biocoenoses. This is expected from the time accumulative character of the taphocoenosis, but the trend is clearly evident in the most disturbed sites which indicated loss of ostracod diversity owing to human impacts. 3.By considering the ecology of most frequent species, multivariate ordination of both tapho- and biocoenoses showed trends within and between lakes in their limnological status, which were related mainly to water chemistry, and also to temporality and eutrophication to a certain extent. Some lakes have apparently lost most of their past ostracod community owing to an increasing trophic status in some cases and to modifications of the hydrological regime in others. Copyright © 2007 John Wiley & Sons, Ltd. [source] | |||||||||||||