1,721,043 research outputs found
Analisi biogeografica del genere Cocconeis (Bacillariophyta) epifita su Posidonia oceanica
No full textANALISI BIOGEOGRAFICA DEL GENERE COCCONEIS (BACILLARIOPHYTA), EPIFITA SU POSIDONIA OCEANICA.
De Stefano M., Licandro P., Procaccini G.
Stazione Zoologica ‘A. Dorhn’
Villa Comunale, 80121 Napoli
[email protected]
Posidonia oceanica è una fanerogama marina endemica del bacino Mediterraneo, dove forma ampie praterie generalmente monospecifiche dalla superficie a circa quaranta metri di profondità. All’interno delle praterie di Posidonia si struttura un complesso ecosistema ricco di specie vegetali ed animali. Le foglie della pianta costituiscono una superficie di colonizzazione ottimale per una complessa comunità macroalgale che risulta quasi interamente costituita da diatomee pennate. La natura dinamica del substrato, le differenti condizioni di irradianza e regime idrodinamico, la competizione per lo spazio, la pressione di grazing nonchè differenze nelle forme di crescita delle stesse diatomee influiscono sulla struttura e dinamica successionale della comunità epifitica presente. Il genere Cocconeis domina in termini di abbondanza specifica.
Nel presente lavoro, le specie ed i taxa infraspecifici di Cocconeis sono state identificate e descritte in 19 comunità epifite di P. oceanica localizzate in differenti aree del Mediterraneo. La percentuale della componente a Cocconeis rispetto al totale delle specie di diatomee presenti, la composizione specifica, l’abbondanza relativa di ciascuna specie e la diversità specifica sono state analizzate in ciascuna delle località campionate. Gli andamenti della distribuzione geografica di tali parametri sono stati letti in rapporto ai patterns di distribuzione filogeografica delle praterie di Posidonia campionate, ottenuti attraverso l’utilizzo di marcatori molecolari (sequenze microsatelliti). A grandi linee le distribuzioni dei parametri analizzati del genere Cocconeis rispondono alla struttura filogeografica esistente in P. oceanica all’interno dell’intero bacino mediterraneo, con una netta divisione fra il bacino occidentale ed il bacino orientale. Nell’ambito del bacino orientale, il settore adriatico mostra notevoli peculiarità, mentre nell’ambito del bacino occidentale si osserva una minore differenza fra il settore centro-settentrionale e quello meridionale.
Ciò suggerisce che le stesse forzanti ambientali che hanno determinato e determinano linee preferenziali di flusso genico fra le praterie di P. oceanica possono anche influenzare la composizione dei popolamenti delle specie ad esse associate
Copepods in a frontal region of the Alboran Sea (January 1997)
No full textThe pelagic ecosystem was investigated in the Alboran Sea during a multidisciplinary international oceanographic expedition on board the RRS Discovery in December 1996 - January 1997. One of the aims of the research was to provide information on the relations between a biotic (physical and hydrological) and biotic(chlorophyll and particulate matter) factors and the spatial distribution of zooplankton in the vicinity of the Almeria-Oran Front. This paper reports the results on the composition and abundance of the copepod community at two stations located on the Atlantic and Mediterranean sides of the Almeria-Oran Front. On both sides of the frontal zone, the dominant copepods were Eucalanus and Pleuromamma together accounting for more than 44% of all copepods. Diel vertical migration of biomass was consistent within the top 500 m of the water column, mainly due to copepods of the genus Pleuromamma
Population ecology of Muggiaea atlantica (Cnidaria, Siphonophora) in the Western English Channel
Full text linkRecent observations suggest that the siphonophore Muggiaea atlantica is expanding its geographical distribution. The mechanisms behind this expansion remain unclear due to our limited knowledge of the species’ ecology. We modelled the functional relationship between the 2 main life-cycle stages of M. atlantica over a 5 yr period (2009?2013) in the Western English Channel. Our aims were to determine the key features of the species’ population dynamics and the influence of local environmental conditions on its population development. Our results highlighted a strong coupling between the timing of specific environmental conditions and the development of the M. atlantica population, thereby explaining interannual differences in the phenology of its blooms. Population development commenced with the initiation of eudoxid production by the overwintering polygastric stages. This reproductive event was linked to the onset of a spring temperature threshold, suggesting a critical basal limit of 10°C for eudoxid production. Interannual variability in the timing of this threshold modulated the degree of mismatch between the developing M. atlantica population and the availability of copepod prey. Unusually cold conditions in the spring of 2010 and 2013 limited the capacity for M. atlantica to initiate eudoxid production leading to poor trophic phasing and the production of single autumn cohorts. In contrast, warmer conditions during spring 2009, 2011, and 2012 facilitated earlier population development, optimal trophic phasing and the production of both summer and autumn cohorts. These findings represent an important addition to our understanding of the ecology of M. atlantica in the Northeast Atlanti
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
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