1,720,959 research outputs found
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
Maternal Investment at the Edge and Centre of Geographical Range: Thermal Tolerance of Females, Embryos and Larvae of Marine Ectotherms
No full textMarine ectotherms are particularly vulnerable to temperature changes and understanding their thermal responses is fundamental to predicting ecosystem functionality in the face of climate change. Reproduction is a key component of an animal’s life cycle; even if adults cope well with environmental change, reproductive females, embryos and larvae may be more vulnerable. Maternal responses to environmental change can have significant, long-lasting effects on performance and success of populations. We studied gravid females, early and late developmental embryos and first stage larvae of two brachyuran mangrove ecosystem engineers, Perisesarma guttatum and Uca urvillei. To assess metabolic responses and maternal effects of populations from the centre and edge of species distributions to acute temperature fluctuations, we studied the thermal windows of embryos, larvae, gravid and non-gravid females from Kenya and South Africa. The metabolic rate was measured for each life stage in the laboratory between 19 and 35°C in water and in air. Additionally, we characterised the field temperatures the animals experience to evaluate species sensitivity to acute temperature change and link it to natural conditions. Results from Kenya indicate that the metabolic rate of gravid and non-gravid females increased with increasing temperature, but gravid females had a higher metabolic rate than non-gravid females for both species. This was sustained over a greater temperature range, indicating females place high investment in viable offspring. P. guttatum late and early stage embryos had higher metabolic rates in water than air, indicating an evolutionary shift towards terrestrial adaptation. The larval stage appeared to be especially robust, with elevated metabolic rates only at very high temperatures. The data indicate that the reproductive component of these species is vulnerable to temperature fluctuations. Elevated temperatures are likely to lead to loss of fitness of females and embryos, with detrimental effects on their populations and loss of ecosystem functionality
È la nicchia termica a determinare il comportamento spaziale degli ectotermi intertidali?
No full textLa temperatura rappresenta la caratteristica ambientale più importante nel determinare la distribuzione degli organismi ectotermi in ambienti acquatici e di transizione, come la fascia intertidale. Mentre le specie sessili possono gestire i forti stress termici tipici di questi ambienti transizionali solo tramite i loro adattamenti fisiologici, gli animali mobili possono accoppiare a questi strategie comportamentali, quali la scelta di aree inondate e non e/o aree più o meno esposte al sole. In questo studio ci siamo chiesti come gli stress termici guidino l’uso dello spazio e del tempo di due specie simpatriche di ectotermi bimodali: i granchi intertidali Uca urvillei (Brachyura, Ocypodidae) e Perisesarma guttatum (Brachyura, Sesarmidae), abbondanti nelle foreste a mangrovie dell’Africa orientale e meridionale. In particolare, abbiamo effettuato uno studio comparato del comportamento spaziale in natura e degli adattamenti fisiologici, in laboratorio, di popolazioni del Kenya e della Repubblica Sudafricana, sottoposte, queste ultime, climi più temperati e ad un regime stagionale. Durante i tre mesi più caldi, entrambe le aree di studio sono state mappate termicamente con l’impiego di logger che registravano in continua temperatura ed umidità. Abbiamo misurato la temperatura corporea di animali focali attivi in natura e osservato i loro pattern comportamentali, valutandone i ritmi di attività e l’uso del microhabitat in cui risiedono. Due strategie spazio-temporali diverse sono emerse sia fra le sue specie analizzate che fra le loro popolazioni in Kenya e Repubblica Sudafricana. L’attività di U. urvillei appare interamente guidata dal ciclo mareale e poco influenzata dalla temperatura. Viceversa P. guttatum, in Kenya modula l’uso dello spazio per minimizzare gli stress termici cui è sottoposta, occupando di fatto sempre zone in ombra e molto umide, mentre le popolazioni sudafricane non hanno evidenziato questo comportamento, probabilmente a causa di un regime termico più fresco. Anche la temperatura corporea rivela una diverso adattamento fra le due specie. Mentre U. urvillei non mostra alcun tipo di termoregolazione, in entrambe le aree di studio, in P. guttatum abbiamo osservato una netta differenza tra popolazioni. In Kenya questo granchio mette in atto strategie di termoregolazione in grado di abbassare la temperatura del corpo, in ambiente aereo, fino a 2°C rispetto a quella ambientale, mentre le popolazioni sudafricane sembrano non avere bisogno di questa strategia. Questo studio rivela che le due specie considerate, pur sfruttando gli stessi microhabitat intertidali di mangrovia, hanno raggiunto livelli di terrestrializzazione totalmente diversi che permettono a U. urvillei di svincolarsi dal problema degli stress termici in ambiente subaereo e di sfruttare a pieno la fascia intertidale in bassa marea, mentre obbligano P. guttatum a mettere in atto strategie comportamentali atte a mitigare gli stessi stress, costringendola ad un uso molto limitato delle aree emerse
Are mangrove crabs true intertid al ectotherms? Different thermal strategies to cope with climate change
No full textTropical intertidal ecosystems such as mangrove forests are particularly vulnerable to climate change since they are at the interface between the marine and terrestrial environments. Crabs are the most important ecological engineers among macrobenthos species in that ecosystem.
They undertake different adaptive strategies to occupy several niches along a terrestrial-marine gradient. Sesarmid crabs, such as Perisesarma guttatum, are exposed to tidal cycles and since they are not a burrowing species, they have to cope with cycling exposition to water and air. Ocypodid crabs, such as Uca urvillei, are burrowers and active only during day low tides. At high tide, they burrow into their holes until the next ebb tide. Through direct observations in the field, we examined the use of time and space of these species and the thermal exposition at low tide, by recording en vironmental temperature. Body temperature was also measured to assess the thermal niche of the animals. Observations indicate that different strategies are employed by each species.
U. urvillei exhibit a broad use of space and time and experience a wide variation in temperature during their feeding, displaying and
homing activities. They consistently visit their burrows, and increase the frequency of visits with the incoming tide. In contrast, P. guttatum, show a restricted use of space, occupying consistently shaded areas and maintaining a very low activity pattern. Body temperature shows clear patterns of thermoregulation for P. guttatum and none for U. urvillei.
Haemolymph oxygen saturation for the former is, nevertheless, very low in air compared to the one of U. urvillei. Moreover, with the incoming tides U. urvillei close the burrows, avoiding water inundation and thriving in air during high tide. We describe two life strategies of two species that occupy similar habitats, but display different physiological and behavioural strategies to thermal stress. These differences might underline the role of these species in the mangrove system for coping with climate induced environmental changes
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
Thermal Response of Mangrove Macrobenthos: Measurement of Population Fitness in Endangered Coastal Systems
No full textClimate change has a strong impact on marine ecosystems, through warming, acidification and hypoxia of seas. Marine ectotherms are mostly affected by changes in temperature, which directly influences their overall fitness. Understanding the thermal response of organisms is therefore crucial to forecast the effects of climate change on ecosystem functionality. Here we focus on the thermal tolerance of adult males, females and gravid females, of two mangrove ecosystem engineers inhabiting the East African mangroves, the crabs Perisesarma guttatum and Uca urvillei. To assess their sensitivity to acute temperature fluctuations across a wide latitudinal gradient, we studied the thermal window of Kenyan and South African populations of both species. The metabolic rate, haemolymph oxygen saturation were measured in the laboratory along a temperature ramp (17-37 °C) in water and in air. Additionally, we characterised the environmental temperature range which the animals are subjected to and compared this to their relative body temperatures measuring their spatio-temporal use in the field. To evaluate the species sensitivity to temperature, we fit these data with the thermal model constructed by our experiments. The different thermal regimes found show different life strategies in the use of time and space. A stenothermic response in water compared to air, with a pronounced latitudinal effect was established, with the South African populations better adapted to lower temperatures than the Kenyan ones. Females with eggs show a higher metabolic rate than males and females with no eggs, representing the most vulnerable adult life stage. The results suggest that these subtropical mangrove populations are vulnerable to long-term increases in temperature, particularly because of reduced oxygen content in water as it warms. This is likely to lead to a loss of fitness with serious consequences for the persistence of such populations and the overall mangrove ecosystem functioning
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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