1,721,007 research outputs found
) in agricultural landscapes
No full textAlthough habitat fragmentation and agricultural intensification are known as threads to pollinator diversity, little is known about consequences for population size and genetic diversity. Here, we combined detailed field observations, molecular approaches and GIS-based quantification of landscape structure (measured by proportions of seminatural habitats and proportions of mass flowering crops) to get new insights into driving forces of population dynamics of the bumblebee species Bombus pascuorum. Comparing 13 agriculturally dominated landscape sectors, we found the proportion of mass flowering crops to positively influence bumblebee abundance whereas the proportion of seminatural habitats was of minor importance. We used microsatellites to quantify landscape-related colony densities, inbreeding and population substructure. Detected colony densities did not correlate with landscape parameters or with local worker abundance, measured by field observations. These results indicate that increased worker abundances within landscapes are rather due to greater colony sizes than due to an increased number of nests. We found significant population substructure, measured by F-ST and seven landscape sectors to bear significantly increased inbreeding values (F-IS). F-IS was strongly varying between sectors but did not correlate with landscape structure. Moreover, F-IS had a significantly negative effect on colony size, demonstrating the importance of genetic diversity on population fitness at a landscape scale. We suggest that inbreeding levels might be related to the temporal variation of food resources and population sizes in agricultural landscapes
The wild honeybees of Sudan - a test case for conservation, apiculture and invasive species
Get PDFWegen des vielfachen Imports von europäischen Honigbienen Apis mellifera und der zufälligen Einführung der Zwerghonigbiene Apis florea in den Sudan, untersuchte ich die möglichen Auswirkungen dieser beiden Arten auf die einheimischen Honigbienen des Sudans. Maternale Introgression in lokale Genpools wurde durch Genotypisierung der mitochondrialen (mt) DNA von wilden Bienenvölkern aus dem ganzen Land erfasst. Die nativen Bienen im Sudan tragen sechs verschiedene mt-Haplotypen (A1 , A4, A8 , A13, O1, O1’). Nur in den Regionen, in denen Imkerei betrieben wird, finden sich auch Bienenvölker mit dem europäischen Haplotyp C2. Obwohl es keine Hinweise auf maternale Introgression durch Schwärmen von Bienenvölkern gibt, findet in Regionen mit kommerzieller Imkerei Introgression in lokale Genpools durch die Paarung von Königinnen mit Drohnen europäischer Herkunft statt. Beide eingeführte Arten haben bisher nicht zu einem Verdrängungswettbewerb mit den nativen Bienen aus dem Sudan geführt. Allerdings hat Apis florea höhere Volksdichten als die einheimischen wilden Kolonien von A. mellifera. Dies deutet darauf hin, dass die Zwerghonigbiene im Sudan ein hohes invasives Potential besitzt.von Mogbel Ahmed Abdalla El-Niweir
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
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
Evolution of innate and social immunity in eusocial bees - [kumulative Habilitation]
No full textDiese Habilitationsschrift gibt in 9 Kapiteln einen umfassenden Überblick zur Evolution des angeborenen Immunsystems eusozialer Bienen (Honigbienen und Hummeln), sowie der Funktion und Evolution der „sozialen“ Immunität. Mittels verschiedener Methoden (Gen- und Genomanalysen, Genexpression, mikrobiologische Tests, Verhaltensexperimente, sowie Metadatenanalyen) wurde die Interaktion zwischen Genetik und Verhalten zur Krankheitsabwehr auf Art- und Populationsebene analysiert. Dieser vergleichende Ansatz erlaubt es generelle Anpassungen eusozialer Bienen und ihre Nutzung natürlicher Ressourcen, für natürliches Krankheitsmangement, besser zu verstehen.The 9 chapters of this Habilitation thesis give a comprehensive overview on the evolution of the innate immune system of eusocial bees (honey bees and bumble bees), as well as of the function and evolution of social immunity. By means of different methods (gene and genome analysis, gene expression, microbiological assays, behavioral experiments and metadata analysis) the interaction of genetics and behavior, to prevent diseases, was analyzed on species and population level. Using this comparative approach, we try to better understand universal adaptations of eusocial bees and their exploitation of natural resources for natural disease management.vorgelegt von Silvio Erle
Of mites and men
Get PDFDie brut-parasitierende Milbe Varroa destructor zerstört Völker der Honigbiene Apis mellifera. Völker, die nicht mittels Akariziden behandelt wurden, sterben typischerweise inhalb von 3 Jahren nach Varroa-Befall. Diese Behandlung entfernt jedoch den selektiven Druck, welcher für die Evolution Varroa-resistenter Merkmale nötig wäre. Wenn Bienenpopulation unbehandlet bleiben, wäre zwar die intiale Völkerverlustrate ziemlich hoch, jedoch könnte in diesem Fall Selektion die Evolution von Resistenzmerkmalen vorantreiben. Innerhalb solcher resistenten Populationen ist die Inhibierung der Reproduktion der Varroa ein gemeinsames Merkmal. Meine Doktorarbeit hatte das Ziel die genomische Basis für die Evolution der Varroa-Resistenz in zwei verschiedenen Honigbienenpopulationen zu untersuchen: einer Population auf Gotland (Schweden) und einer anderen in der Nähe von Toulouse (Frankreich). Ich konnte Gene und physiologische Signalwege identifizieren, welche mit der Resistenz in diesen Populationen in Verbindung stehen. Des Weiteren betrachtete ich, was uns die gefundenen Gene und Signalwege über die Reproduktion der Varroa verraten und welche Folgen diese Ergebnisse für die Zucht Varroa-resistenter Honigbienen haben könnten.The brood-parasitic mite has devastated colonies of the honey bee Apis mellifera. Colonies of A. mellifera, untreated with acaricides, typically die within three years of Varroa infestation. However, this removes the selective pressure for the evolution of Varroa-resistance traits in the bees. Although initial colony losses can be high, when populations are left untreated with acaricides, selection can drive the evolution of resistance traits. Within these resistant populations, the inhibition of Varroa reproductions is a common trait. My PhD aimed to investigate the genomic basis for the evolution of Varroa resistance in two populations of A. mellifera: one from Gotland, Sweden, and the other from near Toulouse, France. I identify genes and physiological pathways linked to resistance in these populations and consider what they can tell us about the reproduction of Varroa as well as the implications of these results for the breeding of Varroa-resistant honey bees.vorgelegt von Benjamin Hanson Conlo
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