1,720,971 research outputs found
Feeding ecology of deep-sea seastars (Echinodermata : Asteroidea): a pigment biomarker approach
No full textResource partitioning and utilisation of phytodetritus by the abyssal mud-ingesting
seastars Styracaster chuni and Hyphalaster inermis were investigated using pigment biomarker analysis. The chlorophyll and carotenoid pigment composition of the stomach content was examined using high-pressure liquid chromatography. No significant differences were observed between the composition of pigments in the 2 species. Both asteroid species utilise the same phytodetrital resource with no apparent partitioning of that resource. Analysis of specific biomarker pigments together with evidence from previous studies suggest that both species ingest small
chlorophytes, cryptomonads, cyanobacteria, coccoliths and diatoms as part of the phytodetrital component of their diet. Phytodetrital material itself is not thought to be an important food source for H. inermis or S. chuni
Feeding ecology of deep-sea seastars (Echinodermata: Asteroidea): a fatty-acid biomarker approach
No full textFatty-acid biomarkers and stomach content analysis were used to investigate the diets of 9 species of deep-sea seastar. Polyunsaturated fatty acids were the most abundant categories of fatty acid contained in the total lipids of all species. They were dominated by 20:5 (n-3) and 20:4 (n 6), with 22:6 (n-3) present in much lower proportions. Monounsaturated fatty acids were also abundant, particularly 20:1 (n-13) and (n-9). Odd-numbered, branched-chain fatty acids and non-methylene interrupted dienes (NMIDs) were present in relatively high levels in all species. Cluster and multi-dimensional scaling (MDS) analyses of the fatty acid composition separated the seastar species into 3 trophic groups; suspension feeders, predators/scavengers, and mud ingesters. Suspension feeders showed greatest reliance on photosynthetic carbon as indicated by the abundance of fatty-acid biomarkers characteristic of photosynthetic microplankton. By contrast, mud ingesters were found to rely heavily on heterotrophic bacterial carbon, containing high percentages of 18:1 (n-7) and NMIDs. Predator/scavengers occupied a trophic position between the suspension feeders and mud ingesters. Zoroaster longicauda, an asteroid of unknown diet, had a similar fatty acid composition to the 3 suspension feeders, Freyella elegans, Brisingella coronata and Brisinga endecacnemos. While the suspension feeders are specialists on benthopelagic copepods, the preferred prey of Z. longicauda is unknown, but is likely to be very similar to that of the suspension feeders. Stomach content analysis revealed the diet of Z. longicauda also includes benthic echinoderms and crustaceans
β-diversity of deep-sea holothurians and asteroids along a bathymetric gradient (NE Atlantic)
Full text linkMeasuring and understanding patterns of ?-diversity remain major challenges in community ecology. Recently, ?-diversity has been shown to consist of 2 distinct components: (1) spatial turnover and (2) species loss leading to nestedness. Both components structure deep-sea macrofaunal assemblages but vary in importance among taxa and ocean basins and with energy availability. Here, we present the first evidence for turnover and nestedness along a bathymetric gradient in 2 major megafaunal taxa, holothurians and asteroids. Turnover is the dominant component of ?-diversity throughout bathyal and abyssal zones in both taxa, despite major differences in ?-diversity and trophic composition. High spatial turnover suggests a role for evolutionary adaptation to environmental circumstances within depth bands. This pattern differs fundamentally from those in some macrofaunal groups in low-energy environments where abyssal nestedness is high and diversity low, with diversity maintained partly by source-sink dynamics
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
Reproductive isolation among morphotypes of the Atlantic seastar species Zoroaster fulgens (Echinodermata:Asteroidea)
No full textZoroaster fulgens is a slope-dwelling seastar species that is distributed throughout the Atlantic Ocean. Studies into the population structure and systematics of marine animals have increasingly found that species with a reported cosmopolitan distribution are, in fact, collections of closely related cryptic or sibling species. In the Porcupine Seabight, three morphotypes of Z. fulgens can be found that have a distribution that is stratified by depth. This study investigates the genetic divergence between these morphotypes using sections of the cytochrome oxidase 1 (COI) and 16S regions of the mitochondrial genome. Bathymetrically separated morphotypes of Z. fulgens are reproductively isolated over distances of approximately 1 km while gene flow occurs among morphotypes, along isobaths, over distances of approximately 900 km. Reproductive isolation on the continental slope may have occurred as a result of selection exerted by gradients of depth-correlated physical factors, such as pressure and temperature. However, allopatric speciation with subsequent range expansion may also explain the observed patterns of genetic divergence. Further investigation of radiation within this group may provide important information on the evolution of slope species. Taxonomic revision of the genus is required
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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