1,720,986 research outputs found
Linking classification boundaries to sources of natural variability in transitional waters: A case study of benthic macroinvertebrates
No full textThe assessment of human impacts on aquatic ecosystems requires separate quantification of natural and anthropogenic sources of environmental variability. This statement is very challenging in some categories of water bodies such as transitional waters, because they are naturally stressed ecosystems in which natural variability occur on different spatial scales (gradients versus patchiness) and temporal scales (regular versus pulse events). Among transitional water quality elements, benthic macroinvertebrates are the most exposed to natural variability patterns due to their life cycles and space-use behavior. In this article, we have evaluated the relevance of different potential sources of natural variability of benthic macroinvertebrate guilds on the temporal and spatial scales and we have quantified their effects on simple and multimetric descriptors of macroinvertebrate guilds; the latter included biomass and numerical densities, taxonomic diversity as well as M-AMBI and index of size spectra, ISS. The study was carried out using the TWReferenceNET database of 14 Eastern Mediterranean and Black Sea lagoons. Synoptic sampling of benthic macroinvertebrates was performed seasonally in different habitats within each lagoon in accordance with a nested design. All considered metrics showed a relatively high degree of variability among different reference stations and ecosystems, with the coefficient of variation ranging from 20% (log numerical density) to 45% (M-AMBI). The average values of every metric were significantly affected by the considered natural sources of variation: lagoon typology, seasonal period and habitat patchiness. Among components of lagoon typology, water salinity influenced the most the variation for both simple and multimetric descriptors. Seasonal period also had a strong influence, with higher values for all metrics before the summer season compared to the one after summer. Benthic habitat patchiness had a considerable influence only on the simple metrics, while continuous habitat variables significantly affected both M-AMBI and ISS. A general mixed model approach, used to quantify the relative influence of the different sources of variation on the considered metrics, allowed calculating type-specific boundaries for M-AMBI and ISS. The new boundaries significantly improved the accuracy of both multimetric indices in the classification of studied reference condition sites, with more than 75% of stations classified as good or high status. Nonetheless, results show that there is an intrinsic uncertainty in the classification of ecological status of lagoon ecosystem due to the degree of variability under reference conditions
Length–mass relationships for transitional water benthic macroinvertebrates in Mediterranean and Black Sea ecosystems
No full textInfluence of hydraulic clam dredging and seasonal environmental changes on macro-benthic communities in the Southern Adriatic (Central Mediterranean Sea)
No full textMacro-benthic communities on the shallowest soft bottoms are impacted by hydraulic dredgers used for the harvesting of the striped venus clam (Chamelea gallina). Changes in macro-benthic assemblages were analysed across four areas in the Southern Adriatic Sea (Central Mediterranean Sea) during the winter and summer 2022 (low and high fishing pressures, respectively). Two sampling surveys were carried out collecting abundance data (N/100m(2)) of 69 species. Diversity indices (Shannon-Weiner and Equitability) were calculated and differences between seasons and areas were tested using non-parametric tests. Changes in the assemblage and feeding habits were explored by adopting permutational multivariate analysis of variance on 34 species. Moreover, environmental conditions of all areas in the two seasons were characterized by a set of 8 variables. Seasonal changes in diversity were only detected for the Shannon-Weiner index, with values significantly higher in winter than summer. Macro-benthic assemblages differed between the two seasons, and the winter assemblages were well-distinct in each area. In contrast, a high overlap was shown in the summer assemblages of the four areas. Changes in feeding habits showed an increase in filter feeding polychaetes and opportunistic/scavenger species during the summer. Temperature, Salinity and primary production were positively correlated to summer stations indicating potential thermic stress on the assemblages. The results provide information on the benthic community impacted by dredge disturbance and seasonal changes driven by environmental conditions, stressing the need to integrate these aspects in assessments on the health status of marine ecosystems required by European directives and fishery management plans
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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