1,721,208 research outputs found
Cascading effects of predatory fish exclusion on the detritus-based food web of a lake littoral zone (Lake Vico, central Italy)
No full textAn exclosure experiment was carried out in the reed-dominated littoral zone of a volcanic lake (Lake Vico, central Italy) to test whether the impact of predatory fish on benthic invertebrates cascades on fungal colonisation and breakdown of leaf detritus. The abundance, biomass, and Shannon diversity index of the invertebrate assemblage colonising Phragmites australis leaf packs placed inside: (1) full-exclosure cages, (2) cages allowing access only to small-sized fish predators, and (3) cageless controls, were monitored over a 45-day period together with the mass loss and associated fungal biomass of leaf packs. The species composition of the fungal assemblage was further assessed at the end of the manipulation. In general, invertebrate predators did not show any significant response to fish exclusion., either on atrophic guild or on a single taxon level. In contrast, the exclusion of large predatory fish induced a diverse spectrum of changes in the abundance and population size-structure of dominant detritivore taxa, ultimately increasing the biomass and Shannon diversity index of the whole detritivorous guild. These changes corresponded with significant variations in leaf detritus decay rates as well as in the biomass and assemblage structure of associated fungal colonisers. Our experimental findings provide evidence that in Lake Vico effects of fish predators on invertebrate detritivores influence the fungal conditioning and breakdown of the detrital substrate. We conclude that in lacustrine littoral zones predator-driven constraints may structure lower trophic levels of detritus-based food webs and affect the decomposition of leaf detritus originated from the riparian vegetation
Role of microorganisms and macrofauna in benthic phosphorus dynamics in the po river--Adriatic Sea frontal system: An experimental approach
No full textSediment biotic and abiotic attributes were determined during the PRISMA II oceanographic campaigns in the northern and central Adriatic Sea. The radiotracer orthophosphate 32 P was used under laboratory conditions to analyse the role of micro- and macrofauna in phosphorus dynamics at the water-sediment interface. Effects of infaunal suspensivores on microfungal growth were also investigated. Our findings emphasised: 1) significant differences in sediment 32 P uptake as related to the sampling area, occurrence of the pelagic frontal system, sediment grain size, microbial activity, and anoxia; 2) the crucial role played in 32 P dynamics by different tropho-functional groups r - r i.e ., infaunal filter-feeders and epifaunal detritivore characterising the benthic community of the northern Adriatic basin. The significant changes in ergosterol concentration (adopted as an index of microfungal growth) observed in sediments subjected to infaunal activity, eventually provided a comprehensive insight into macrofauna-microorganism interactions. The potential impact of macrofaunal activity in phosphorus dynamics in the Adriatic benthic system is discussed
Indirect, size-dependent effects of crustacean mesograzers on the Rhodophyta Gracilaria verrucosa (Hudson) Papenfuss: evidence from a short-term study in the Lesina Lagoon (Italy)
No full textIn the Lesina Lagoon (southern Italy), three species of crustacean mesograzers - the isopods Idotea baltica Pallas and Sphaeroma serratum Fabricius, and the amphipod Gammarus us insensibilis Stock - dominate the epifaunal assemblage associated with the Rhodophyta Gracilaria verrucosa (Hudson) Papenfuss. We examined in laboratory feeding assays the palatability of the red macroalga to each of the three mesograzer species. Furthermore, we used a cage experiment to investigate the actual impact of the mesograzer assemblage on the growth of Gracilaria under field conditions. Cages with different mesh sizes were used to test the hypothesis that mesograzer effect on the macroalga is size dependent. Laboratory assays indicated for all the mesograzer species a negative effect on Gracilaria; in particular, I. baltica and G. insensibilis actively consumed the macroalga, whereas S. serratum grazing activity was weaker but nonetheless statistically significant. In contrast, Gracilaria was not significantly grazed under field conditions. When mesograzers were totally excluded, algal growth showed a strong negative variation compared to controls where access was not precluded (ca. 43%. reduction in wet mass). Simultaneously, the abundance of the encrusting bryozoan Conopeum seurati increased significantly (from 1.5 to 24.7 mg g(-1), corresponding to 1.7% and 28.9% cover of algal surface); an analogous increase was detected in the abundance of other sessile macrofauna (i.e. the bivalve Mytilaster marioni). When only juvenile, small-sized epifauna were given access to Gracilaria, algal mass change was reduced by around 36%. The abundance of both encrusting bryozoans and sessile bivalves showed significant positive variations, close to those observed in the total exclusion treatment. Our results suggest that, even though Gracilaria represents a potentially palatable resource for mesograzers in the Lesina Lagoon, the actual impact of epifauna on the macroalga might be beneficial, through an indirect control on the development of fouling epibionts. In addition, such a positive effect may be size specific, since the juvenile, small-sized component of the mesograzer assemblage exerted a significantly weaker control on fouling development, even at unnaturally high densities. We suggest that the occurrence of different functional roles among mesograzer size classes might represent a significant controlling factor for the establishment of mesograzer-epibiont-host plant interactions, and for their effects on macrophytal productivity
Sediment structural properties mediating dominant feeding types patterns in soft-bottom macrobenthos of the Northern Adriatic Sea
Full text linkIn sediments sampled in Northern Adriatic Sea invertebrate benthic macrofauna was examined in comparison with both substratum bulk parameters (average grain size, sorting, total organic matter content) and attributes of grain size classes (specific organic matter content of dimensional fractions). The aims were: 1) to determine whether variations of community overall parameters (total spatial density, number of taxa) and in numerically dominant feeding types (deposit-feeders and suspension-feeders) patterns were related to changes in sediment general properties; 2) to evaluate whether the observed patterns of abundance for deposit- and filter-feeders had more valid correlates in specific properties of substratum dimensional fractions. Number of taxa and animal spatial density resulted conventionally related to substratum bulk parameters while feeding types patterns in comparison with sediment total organic matter content exibited a reciprocal negative effect; only when both feeding types and sediment structure were resolved to their specific attributes in terms of prevalence of tubicolous taxa among deposit-feeders and organic matter richness of single dimensional fractions, the analysis emphasized patterns unequally affected by specific size fractions abundance and organic matter content: deposit feeders demonstrated to be related to the presence in the substrate of intermediate grain size classes necessary for tube-building. Those intermediate fractions proved to be more adequate descriptors than average grain size or other overall sediment parameters per se of relations actually established between feeding types and the complex nature of bottom sediments. Our results emphasize that for Northern Adriatic Sea benthic communities, sediment organic matter content may represent a factor of minor importance in comparison with other substrate attributes, for which it may be necessary a detailed analysis of sediment structure. Thus, we concluded that the complexity of soft-bottom communities may defy any simple paradigm relating macrobenthic patterns to any single sediment bulk attribute, and we propose a shift in focus towards an higher resolution of both functional groups in macrobenthic associations las already suggested in other investigations) and of substratum structural description
Role of macrodetrivores-detritus trophic relationships in phosphorus dynamics at the marine water-sediment interface: laboratory experiments using 32P.
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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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