1,720,967 research outputs found
Food-web and climate-related dynamics in the Baltic Sea: present and potential future applications in fish stock assessment and management
No full textThe human infl uence on marine ecosystems is being recognized as a basis for extending the horizons of management. Historical anthropogenic infl uence has involved a wide variety of factors, including the effects of fi shing on the dynamics of individual resource species. More inclusive complexity includes the interactions among species, and their interactions with other aspects of their biotic and physical environment. In this chapter, we review these elements of complexity for the central Baltic Sea. This ecosystem has a long history of human infl uence and its own special characteristics, due to its geographic location, geomorphic traits, and socio-political context. More and more of the complexity of this ecosystem is being recognized as scientists add to the wealth of documentation regarding the infl uence of surrounding terrestrial activities, monitor the dynamics of component populations, establish the effects of weather and climate, and illuminate the relationships among the various elements of the ecosystem. There is a great deal of historical information to characterize the changes that have occurred, not only among the various species making up the ecosystem, but also at the ecosystem level. Some of these have involved regime shifts, in part owing to climatic factors. Such significant changes involve more than one of the ecosystem’s trophic levels as well as physical features such as salinity, temperature, and oxygen concentration. We begin to understand some of the complexity of ecosystems when we recognize that such factors are not alone, however, and realize that trophic cascade dynamics and feedback loops are also involved. Of particular importance for fi sheries management is the clarity with which we have observed, documented, and explained some of the effects of fi shing, not simply as an infl uence on individual resource species, but on the ecosystem as a whole. Some of these ecological aspects are currently used in fi sh stock assessment and management in the central Baltic Sea, but recently acquired additional knowledge could be potentially used in the future to reach the goal of a sustainable exploitation of fi sheries resources in this area
REGIME SHIFTS IN MARINE ECOSYSTEMS: HOW OVERFISHING CAN PROVOKE SUDDEN ECOSYSTEM CHANGES
No full textRegime shifts, i.e. sudden changes in the structure and function of ecosystems, are of growing concern for fisheries management. This workshop reviewed the present state of our understanding of regime shifts in marine ecosystems, focusing on shifts which largely took place as a result of overfishing. The workshop presented examples of shifts in overexploited marine ecosystems around the world and provided recommendations for management responses. Two case studies discussed the Baltic and Black Sea ecosystem shifts, which are among the most prominent regime shifts recorded so far
Within-system spatial variation in drivers of exploited marine ecosystem regime shifts
No full textComparative analyses of the dynamics of exploited marine ecosystems have
led to differing hypotheses regarding the primary causes of observed regime
shifts, while many ecosystems have apparently not undergone regime shifts.
These varied responses may be partly explained by the decade-old recognition
that within-system spatial heterogeneity in key climate and anthropogenic drivers
may be important, as recent theoretical examinations have concluded that
spatial heterogeneity in environmental characteristics may diminish the tendency
for regime shifts. Here, we synthesize recent, empirical within-system
spatio-temporal analyses of some temperate and subarctic large marine ecosystems
in which regime shifts have (and have not) occurred. Examples
from the Baltic Sea, Black Sea, Bengula Current, North Sea, Barents Sea and
Eastern Scotian Shelf reveal the largely neglected importance of considering
spatial variability in key biotic and abiotic influences and species movements
in the context of evaluating and predicting regime shifts.We highlight both the
importance of understanding the scale-dependent spatial dynamics of climate
influences and key predator–prey interactions to unravel the dynamics of
regime shifts, and the utility of spatial downscaling of proposed mechanisms
(as evident in the North Sea and Barents Sea) as a means of evaluating
hypotheses originally derived from among-system comparisons
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Development of a Scoring System to Evaluate the Severity of Craniocervical Spinal Cord Compression in Patients with Mucopolysaccharidosis IVA (Morquio A Syndrome).
No full textDispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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