1,720,983 research outputs found
Effects of the feeding functional response on phytoplankton diversity and ecosystem functioning in ecosystem models
Get PDFOcean ecosystems are under pressure from the needs of a growing human population and from global environmental change. A concurrent loss of diversity observed across ecosystems raises the question of how diversity influences ecological and biogeochemical processes of ecosystems. Little is known about controls of diversity and its role in shaping ecosystem processes in the global pelagic ocean and biogeochemical cycles of nutrients and carbon. Bottom-up controls by nutrient availability and use have previously been investigated using a novel global ecosystem model which resolves phytoplankton diversity. Top-down effects of zooplankton feeding as an important mechanism able to promote diversity have not yet been investigated on the global scale. Also, the influence of diversity on primary production and other indicators of ecosystem functioning in the global ocean are not well understood. The present thesis aims to extend our understanding of how zooplankton feeding influences phytoplankton diversity in ecosystem models. In addition, it addresses the question of how diversity may influence ecosystem functioning and biogeochemical cycling. The first part of the thesis examines the top-down control of zooplankton feeding on phytoplankton diversity in a global ocean ecosystem model with a self-assembling hytoplankton community. In simulations with different mathematical formulations for feeding, phytoplankton diversity differs by more than a factor of three. A sigmoidal Holling type 3 functional response implying preferential grazing on the most abundant prey creates refuges for phytoplankton at low abundances and punishes dominant types. The resulting seasonal succession is in better agreement with observations than for a type 2 functional response without preferential grazing. Simulations with different diversity also differ in primary production and net community production on the annual scale. The second part investigates the effects of phytoplankton diversity on primary production as a basic ecosystem function in the pelagic ocean. Global simulations with different levels of diversity are complemented by idealised simulations without environmental forcing. A positive relationship between diversity and productivity is found for simulations using type 3 feeding. In these simulations, the phytoplankton community is characterised by a complementary use of resources. Higher diversity increases primary production only in temperate, but not in oligotrophic oceanic regions, indicating a potentially important influence of the nutrient supply. No effect of diversity on primary production can be identified for a type 2 feeding functional response. The sensitivity of the simulated diversity to the feeding formulation motivates the development of an alternative zooplankton feeding model presented in the third part of this thesis. The commonly employed functional responses used in the previous parts are simplistic with regard to the feeding process and to the zooplankton community structure in the ocean. The model presented here addresses the first aspect by taking into account metabolic constraints on the feeding process. Energy obtained from predation is optimally allocated between foraging activity and the assimilation of food to maximise net growth. The model captures experimental feeding data for different zooplankton taxa. It provides an alternative approach for representing plankton dynamics in a seasonally stratified mixed layer without an otherwise required shift in community structure. The fourth part of this thesis complements the main model-based focus of zooplankton feeding and diversity with an experimental approach addressing the impact of feeding within a community. This study investigates herbivorous and carnivorous feeding relationships with a sea-ice community as a model system. It presents grazing experiments using natural communities of different algal taxa instead of individual predator-prey combinations, as well as predation experiments. The experiments reveal complex feeding relationships and estimate the feeding impact of sea-ice meiofauna on the sea-ice community. Similar experiments for plankton would provide valuable information for enhancing our understanding of feeding in a community context and ultimately help in developing future zooplankton feeding models. The different aspects of zooplankton feeding and phytoplankton diversity addressed in this study demonstrate the influence of top-down controls on diversity, and indicate consequences for ecosystem functioning and biogeochemical cycling. A better understanding and representation of the complex feeding processes in the plankton will enhance our ability to model diversity in the pelagic ocean. Resolving diversity may be an important component in predicting biogeochemical cycling in a future ocean
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
Model of optimal current feeding in zooplankton
Get PDFZooplankton feeding formulations in plankton models have exclusively focused on the relation between food concentration and ingestion, with respiration and excretion being treated separately, despite experimental evidence for strong links among these processes. We present an optimal current-feeding model linking ingestion, respiration, and assimilation efficiency to foraging activity. The Ivlev model is a special case of our optimal current-feeding model, which applies to static feeding behaviour. We validate our model with experimental data for copepods, ciliates, and dinoflagellates. Parameter estimates suggest that phylogenetic grouping is more important than predator size in determining feeding behaviour. Respiratory costs of foraging, e.g. for generating a feeding current, may be much larger than previously thought, are larger in smaller organisms, and might explain the independent development of feeding thresholds in different micro- and mesozooplankton groups. Both preferential feeding on, and lower feeding thresholds for, larger food particles are predicted to derive from greater capture efficiency owing to enhanced detectability of larger particles. The relation between feeding threshold and prey size appears to depend on feeding strategy but not on predator size, as a common relationship seems to apply for current feeders (ciliates and copepods) spanning a vast size range. Our model exhibits an inverse relationship between ingestion and assimilation efficiency, reducing the contribution of copepods to export of organic matter relative to remineralisation at low food concentrations. Export ratio variations previously thought to require strong shifts in community composition can be generated by changes in feeding behaviour predicted by our model
Dispelling 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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