1,721,114 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
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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Stress hormones, foraging energetics, and wind-use patterns in two sympatrically breeding southern albatrosses
Full text linkThe modulation of energy balance through physiological or behavioral adjustments (i.e., allostasis) allows organisms to cope with unexpected challenges, ensuring reproductive success and survival. However, energetic challenges can be exacerbated during critical life stages such as breeding, when more resources are needed to feed offspring. Amphibious marine organisms like seabirds already face a unique challenge of finding patchily distributed ephemeral prey within a vast, dynamic ocean and delivering prey to hungry chicks at land-based nests. With the depletion of ozone and rising sea temperatures, atmospheric and oceanographic disruptions are escalating, affecting the distribution of prey in addition to altering windscapes that seabirds, like the glider-shaped albatrosses, rely on for traveling. Metabolic stress hormones in seabirds can be used to indicate adverse changes within the environment; however, the functional role of stress hormones is confounded by factors such as species, life history, or breeding stage. In chapter 2, I used structural equation models to improve our understanding of the role of corticosterone, a stress hormone, as a mediator of energy balance in two sympatric breeding albatrosses during incubation and early-chick-rearing stages. Campbell (Thalassarche impavida) and grey-headed albatrosses (T. chrysostoma) are annual and biennial breeders, respectively, that occupy differing prey niches. By measuring foraging behavior, mass change, and hormone levels, I found that corticosterone concentrations before and after foraging trips were similar between species and across stages, potentially because of behavioral flexibility or different corticosterone functional roles across stages. However, when parents were provisioning small chicks during the guard stage, the former were more sensitive to changes in energy balance, suggesting that hormone concentrations elicited during this stage are indicative of foraging conditions. Also, pre-trip corticosterone may determine foraging destination in incubation-stage Campbell albatrosses, but it remains unclear if this mediates foraging success. In chapter 3, I examined the role of environmental interactions, behavioral flexibility, and morphological constraints on energy balance during early chick-rearing using the doubly labelled water method to estimate the daily energy expenditure (DEE) of GPS tracked individuals. In both species, greater DEE was associated with greater foraging success, lower mean wind speeds during water take-offs, a greater proportion of strong tailwinds (> 12 ms-1), and younger chick age. Greater foraging success was marginally costlier in male albatrosses of both species and DEE was higher in grey-headed albatrosses when they experienced a greater proportion of strong headwinds. Climate models predict wind speeds will weaken in the foraging range of female Campbell albatrosses and intensify in the range of grey-headed and male Campbell albatrosses, thus breeding costs may increase for both species. In chapter 4, I used a flight cost function to show that mean flight costs were greater during the incubation stage for grey-headed albatrosses, which may interrupt breeding cycles. I then used reanalyzed wind data in combination with bird-borne GPS tracking data to score the cost of flight path trajectory choices and to calculate vector correlation coefficients to evaluate wind-use consistency. Greater wind-use consistency resulted in lower mean flight costs and greater foraging success for both species, but Campbell albatrosses that use low-wind regions had the greatest wind-use consistency. Males of both species gained less mass than females when making similar cost choices during incubation stage transit. Chick-rearing individuals of both species traded greater cost choices for greater foraging success during outbound transit. Overall, foraging strategy, mediated by hormones and morphology, revealed energetic vulnerabilities with respect to species, sex, and breeding stage
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Comparative non-breeding foraging ecology of surface foraging kittiwakes (Rissa sp.) and deep diving thick-billed murres (Uria lomvia)
Full text linkThe non-breeding period is a critical life history period for seabirds, as individuals need to regain body condition lost while breeding. Where animals move is driven by a myriad of factors that can be divided into intrinsic factors, which are linked to physiological and life-history traits, and extrinsic factors which occur as the result interactions with other animals or the environment. To better understand the challenges of wintering in the North Pacific marine ecosystem, I studied the migrations and foraging ecology of three species, surface foraging black-legged kittiwakes (Rissa tridactyla) and red-legged kittiwakes (R. brevirostris), and deep-diving thick-billed murres (Uria lomvia) from three colonies in the southeastern Bering Sea. I tracked birds with geolocation loggers and time-depth recorders over three winters with contrasting environmental conditions (2008-2011). Remotely-sensed environmental data was used to highlight the effects of changing conditions both intra- and inter-annually, while stable isotope values of carbon and nitrogen from feather tissue were used to infer dietary trophic level and niche partitioning. In Chapter 1, I contrasted red-legged and black-legged kittiwake wintering ecology across the spatial, behavioral and dietary niche dimensions and found significant partitioning; red-legged kittiwakes showed greater specialization across all niche dimensions and depended almost exclusively upon on the Bering Sea ecosystem. In Chapter 2, I assessed individual winter foraging strategies of thick-billed murres using a combination of spatial, stable isotope, and behavioral data. Both annual and body size differences largely determined strategies, with some larger bodied birds from St Paul using a deeper daytime diving and more residential strategy unexploited by smaller birds. In Chapter 3, I contrasted intrinsic drivers (e.g. sex, breeding colony and experience) with the influence of annual habitat conditions on black-legged kittiwake winter distributions. I found large annual differences in distributions that spanned the sub-arctic North Pacific, yet in consecutive winters individuals returned to the same regions more often than expected. Overall, environmental conditions played a significant role in influencing the movements and behavior of individuals, however life history characteristics in consecutive winters such as sex, dietary preference or body size sometimes constrain individual wintering ecology
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The foraging ecology of seabirds in relation to contaminant exposure and oceanographic habitat
Full text linkThe vastness of the ocean makes it difficult to study. This is compounded by regional differences in temperature, wind patterns, underwater topography, and primary productivity that extend from the ocean’s surface to depths of thousands of meters. Many organisms that inhabit the marine environment navigate many environmental changes as they move between regions in both the horizontal and vertical directions. The ability to navigate through different habitat types indicates that marine animals may be adaptable to multiple environments; however, it also suggests that they may be exposed to multiple hazards, including hazards of anthropogenic origin. Rates of anthropogenic inputs of chemicals and litter to the atmosphere and the ocean are increasing. However, many effects of anthropogenic compounds on marine life are only beginning to be understood. In this dissertation, I assessed foraging ecology, contaminants, and the effects of contaminants, in seabirds, which are unique among marine animals because they hunt for fishes and squid from the air, but breed on land. Land-based breeding enables them to be easily studied, and they are good samplers of the vast ocean because they travel tens to thousands of kilometers from the breeding colony to forage. I first tested the hypothesis that seabirds’ foraging behaviors are related to local oceanographic habitats, and that they exhibit behavioral plasticity to exploit the marine environment. GPS-tracking and remotely-sensed environmental data of four species of boobies (Sula spp.) demonstrated adaptable behaviors that changed depending on the type of oceanographic habitat in which boobies foraged (e.g. based on depth, sea surface temperature and topography). Second, I measured blood-based persistent organic pollutants (POP) and mercury contaminant concentrations in boobies and two species of frigatebirds (Fregata spp.) from four colonies in the Pacific Ocean and Caribbean Sea. I combined blood-based contaminant measurements with two measures of foraging ecology (blood-based stable isotopes and GPS-tracking). Boobies and frigatebirds were exposed to different contaminants depending on their foraging habitat (e.g. nearshore vs offshore). Though three of the study sites were remote and uninhabited, all birds had contaminants. Lastly, I tested the hypothesis that mercury would negatively affect seabirds’ breeding. I measured breeding in Flesh-footed Shearwaters (Ardenna carneipes) and Great-winged Petrels (Pterodroma macroptera) in the Southern Ocean (Western Australia). Though Great-winged Petrels’ blood mercury concentrations were the highest among all seabirds, I did not detect relationships between mercury and breeding in either species. Overall, seabirds are adaptive to their local marine environment. They traverse many habitat types while foraging, which influences the concentrations and types of contaminants that they encounter. However, they may be adapted, or tolerant, to some contaminants like mercury. Seabirds are good samplers of the marine environment, and continue to serve as good indicators of oceanographic processes and contaminants found in the ocean
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Comparative behavior, diet, and post-breeding strategies of two sympatric North Pacific albatross species (Phoebastria sp.)
Full text linkA fundamental condition of the struggle for existence is resource limitation. Optimal foraging theory describes how individuals refine behavior to most efficiently exploit available resources. For colonial breeding animals, such as seabirds, competition for limited resources is amplified by a high density of competitors at feeding grounds near the colony, which can lead to a diversification of foraging strategies that best exploit available resources. Laysan and black-footed albatrosses (Phoebatria immutabilis and P. nigripes, respectively) breed sympatrically and synchronously in dense colonies on small atolls throughout the northwestern Hawaiian Islands. While the distributions and habitat preferences of these congeners are well described, the variability in foraging strategies driven by niche partitioning is not. In chapter 1, I used fine-scale behavioral data from GPS data-loggers to tease apart subtle behavioral nice partitioning between and within Laysan and black-footed albatrosses constrained to poor-nutrient tropical waters during the most energetically-demanding reproductive stage in birds: the brood-guard. Albatrosses showed discrete behavioral partitioning both between and within species, which was driven by differences in nocturnal and diurnal foraging and by sex-specific strategies. Black-footed albatrosses exhibited greater variability in foraging patterns suggesting they may experience strong intraspecific competition at Tern Island. In chapter 2, I employed a novel adaptation of a biochemical diet analysis, quantitative fatty acid analyses, to investigate dietary niche partitioning across the breeding season. This analysis characterized diet of individual adult albatrosses across the breeding season, from incubation to the chick-brood, for the first time in these species. Additionally, this research extended beyond diet characterization to quantify dietary dependence on fisheries-associated resources for these two species. One of the primary threats to albatross is the incidental mortality of birds from fisheries bycatch, therefore, understanding the incidence of fisheries-associated food in the diet of a breeding colony of albatrosses could have important conservation implications. While older birds tended to consume more squid than younger birds, we did not identify an age bias in birds that exploited fisheries resources. Parallel with results from the behavioral analysis in chapter 1, I found that black-footed albatrosses had greater dietary flexibility than Laysan albatrosses at a population level, and a greater degree of dietary specialization at the individual level. In the final chapter, I looked at how the obligatory act of flight feather molt impacted activity levels and space use across the post-breed migrations, when albatrosses are freed from central place foraging constraints, but limited by demands of self-maintenance. I found that activity levels, but not habitat use, were impacted by molt extent. Habitat use appeared to be primarily driven by consistent individual preferences, with birds showing a high degree of site fidelity to their post-breeding molting grounds. A clear decrease in home range size with age indicated that birds spend less time searching for profitable feeding grounds when they are older, likely a product of accumulated memory and experience in these long-lived species
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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