1,403 research outputs found
Regeneration by seeds and vegetation structure in alpine plant communities, subarctic Finland
No full textAbstractThe aims were to examine the importance of regeneration by seeds, the influence of plant traits and disturbances, and the role of seed-seedling conflicts in regeneration and in the determination of vegetation structure. The study was carried out at in a subarctic alpine area (Kilpisjärvi 69°01′N 20°50E′, Finland).Seed bank and seedling densities were high in many plant communities (ranges 99–1109 viable seeds/m² and 0.2–227 seedlings/m², respectively). Effective seedling recruitment is reflected in vegetation as a high proportion of plants with poor or no vegetative reproduction ability. This development may take place in meadows and snowbeds where herbs (e.g. Gnaphalium supinum, Sibbaldia procumbens, Veronica alpina and Viola biflora) are abundant. On the other hand, the low proportion of these plants in heath vegetation reflects ineffective seedling recruitment.Floristic similarities between the consecutive phases in the regeneration pathway may be low despite effective seedling recruitment. Clonality, large and small seed sizes and appendaged diaspores limit the movement of species from phase to phase.Generally, disturbances facilitate effective regeneration by seeds. Grazing promotes species with large seed banks and is therefore one reason for high seed bank densities. Freezing and melting processes negate a negative influence of altitude on seed bank densities in the phase of seedlings. However, if disturbances are severe and continuous and the soil is compact, unstable or dry, disturbances are not beneficial. The same is true if there is a shift in the species composition of seedlings from gaps to closed vegetation. This phenomenon occurred in a rich meadow.Seed-seedling conflicts limit regeneration by seeds in low-herb snowbeds and Ranunculus glacialis-Gymnomitrion snowbeds. Vegetative reproduction and infrequent pulses of seedling recruitment negate an influence of short-term seedling recruitment on the spatial structure of vegetation. Extreme conditions, such as low temperatures, instability of the soil and late snowmelt modify the influence of factors that are important in more moderate conditions.To conclude, all transitions limit regeneration by seeds. However, favourable conditions (e.g. moist conditions in a meadow) partly eliminate the obstacles against seedling emergence. Regeneration by seeds therefore has a major impact on the dynamics and structure of vegetation. In heath vegetation, where bare soils are dry and the moss cover is thick, large seed banks and seed rains do not guarantee effective seedling recruitment. The regeneration process is reduced in the early phases, and plants that reproduce primarily by seeds have a minor role in vegetation. The accumulation of seed banks is effective in these circumstances.Academic Dissertation to be presented with the assent of the Faculty of Science, University of Oulu, for public discussion in Kuusamonsali (Auditorium YB 210), Linnanmaa, on November 15th, 2002, at 12 noon.Abstract
The aims were to examine the importance of regeneration by seeds, the influence of plant traits and disturbances, and the role of seed-seedling conflicts in regeneration and in the determination of vegetation structure. The study was carried out at in a subarctic alpine area (Kilpisjärvi 69°01′N 20°50E′, Finland).
Seed bank and seedling densities were high in many plant communities (ranges 99–1109 viable seeds/m² and 0.2–227 seedlings/m², respectively). Effective seedling recruitment is reflected in vegetation as a high proportion of plants with poor or no vegetative reproduction ability. This development may take place in meadows and snowbeds where herbs (e.g. Gnaphalium supinum, Sibbaldia procumbens, Veronica alpina and Viola biflora) are abundant. On the other hand, the low proportion of these plants in heath vegetation reflects ineffective seedling recruitment.
Floristic similarities between the consecutive phases in the regeneration pathway may be low despite effective seedling recruitment. Clonality, large and small seed sizes and appendaged diaspores limit the movement of species from phase to phase.
Generally, disturbances facilitate effective regeneration by seeds. Grazing promotes species with large seed banks and is therefore one reason for high seed bank densities. Freezing and melting processes negate a negative influence of altitude on seed bank densities in the phase of seedlings. However, if disturbances are severe and continuous and the soil is compact, unstable or dry, disturbances are not beneficial. The same is true if there is a shift in the species composition of seedlings from gaps to closed vegetation. This phenomenon occurred in a rich meadow.
Seed-seedling conflicts limit regeneration by seeds in low-herb snowbeds and Ranunculus glacialis-Gymnomitrion snowbeds. Vegetative reproduction and infrequent pulses of seedling recruitment negate an influence of short-term seedling recruitment on the spatial structure of vegetation. Extreme conditions, such as low temperatures, instability of the soil and late snowmelt modify the influence of factors that are important in more moderate conditions.
To conclude, all transitions limit regeneration by seeds. However, favourable conditions (e.g. moist conditions in a meadow) partly eliminate the obstacles against seedling emergence. Regeneration by seeds therefore has a major impact on the dynamics and structure of vegetation. In heath vegetation, where bare soils are dry and the moss cover is thick, large seed banks and seed rains do not guarantee effective seedling recruitment. The regeneration process is reduced in the early phases, and plants that reproduce primarily by seeds have a minor role in vegetation. The accumulation of seed banks is effective in these circumstances
The Wetland Book, Volume I: Structure and Function, Management and Methods
No full textAn edited volume coving all aspects of wetlands, Volume 1 doing as the subtitle suggests: Structure and Function, Management and Methods. Mark Everard has been sole or lead author on 40 chapters in the Wetland Book and junior author in a number of others
New taxa and geographic variation of western North American butterflies: based on specimens in the C. P. Gillette Museum of Arthropod Diversity, Colorado State University
No full textSome parts authored by Ken E. Davenport, Norbert G. Kondla, Paul A. Opler, and Michael S. Fisher.Includes bibliographical references.During the two winters of 2016-2017, Scott volunteered to curate the butterflies in the C. P. Gillette Museum of Arthropod Diversity (CSUC), at Colorado State University, Fort Collins, Colorado. After more than 700 hours of identifying and sorting ~30,000 butterflies, all are arranged by species and identifiable subspecies, except for various tropical and Palearctic groups beyond Scott's expertise. Studying the specimens revealed some unnamed (identifiable) subspecies, and documented the geographic variation of many species. New research discoveries are reported here
Harmony and discord within the English ‘counter-culture’, 1965-1975, with particular reference to the ‘rock operas’ Hair, Godspell, Tommy and Jesus Christ Superstar
No full textPhDThis thesis considers the discrete, historically-specific theatrical and musical sub-genre of ‘Rock Opera’ as a lens through which to examine the cultural, political and social changes that are widely assumed to have characterised ‘The Sixties’ in Britain. The musical and dramatic texts, creation and production of Hair (1967), Tommy (1969), Godspell (1971), Jesus Christ Superstar (1970) and other neglected ‘Rock Operas’ of the period are analysed. Their great popularity with ‘mainstream’ audiences is considered and contrasted with the overwhelmingly negative and often internally contradictory reaction towards them from the English ‘counter-culture’. This examination offers new insights into both the ‘counter-culture’ and the ‘mainstream’ against which it claimed to define and differentiate itself.
The four ‘Rock Operas’, two of which are based upon Christian scriptures, are considered as narratives of spiritual quest. The relationship between the often controversial quests for re-defined forms of faith and the apparently precipitous ‘secularization’ and ‘de-Christianization’ of British society during the 1960s and 1970s is considered.
The thesis therefore analyses the ‘Rock Operas’ as significant, enlightening prisms through which to view many of the profound societal debates – over ‘faith’ and ‘belief’ in the widest senses, sexuality, the Vietnam war, generational conflict, drugs and ‘spiritual enlightenment’, and race – which were, to some considerable extent, elevated onto the national, political agenda by the activities of the broadly-defined ‘counter-culture’. It considers subsequent representations of the ‘counter-culture’ as the root of a contested but enduring popular legacy of ‘The Sixties' as a period of profound cultural change
Efficient and Flexible Spatiotemporal Clutter Filtering of High Frame Rate Images Using Subspace Tracking
No full textCurrent methods to measure blood flow using ultrafast Doppler imaging often make use of a Singular Value Decomposition (SVD). The SVD has been shown to be an effective way to remove clutter signals associated with slow moving tissue. Conventionally, the SVD is calculated from an ensemble of frames, after which the first dominant eigenvectors are removed. The Power Doppler Image (PDI) is then computed by averaging over the remaining components. The SVD method is computationally intensive and lacks flexibility due to the fixed ensemble length. We propose a method, based on the Projection Approximation Subspace Tracking (PAST) algorithm, which is computationally efficient and allows us to sequentially estimate and remove the principal components, while also offering flexibility for calculating the PDI, e.g. by using any convolutional filter. During a functional ultrasound (fUS) measurement, the intensity variations over time for every pixel were correlated to a known stimulus pattern. The results show that for a pixel chosen around the location of the stimulation electrode, the PAST algorithm achieves a higher Pearson correlation coefficient than the state-of-the-art SVD method, highlighting its potential to be used for fUS measurements.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Signal Processing System
High Frequency Functional Ultrasound in Mice
No full textFunctional ultrasound (fUS) is a relatively new imaging modality to study the brain with a high spatiotemporal resolution and a wide field-of-view. In fUS detailed images of cerebral blood flow and volume are used to derive functional information, as changes in local flow and/or volume may reflect neuronal activation through neurovascular coupling. Most fUS studies so far have been performed in rats. Translating fUS to mice, which is a favorable animal model for neuroscience, pleads for a higher spatial resolution than what has been reported so far. As a consequence the temporal sampling of the blood flow should also be increased in order to adequately capture the wide range in blood velocities, as the Doppler shifts are inversely proportional to the spatial resolution. Here we present our first detailed images of the mouse brain vasculature at high spatiotemporal resolution. In addition we show some early experimental work on tracking brain activity upon local electrical stimulation.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Signal Processing System
Environmental and Parental Influences on Offspring Health and Growth in Great Tits (Parus major)
No full textPMCID: PMC3728352This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Analysis of the RNA-binding properties of Hfq proteins from the bacteria Escherichia coli, Listeria monocytogenes, and Caulobacter crescentus
No full textBacterial small, noncoding (s)RNAs play important roles in post-transcriptional gene regulation through complementary base-pairing interactions with target messenger (m)RNA molecules,. Many sRNAs rely on protein partners to carry out their regulatory functions. As such, the interactions between proteins and small RNAs contribute to gene regulation across all three domains of life. In particular, the hexameric RNA chaperone protein, Hfq, has been shown to mediate interactions between bacterial small (s)RNAs and their target mRNAs as a part of bacterial stress responses. Hfq orthologues have been characterized in approximately half of all sequenced bacterial species. This protein functions to stabilize sRNA steady-state expression levels, protect sRNAs from cleavage, accelerate efficient base pairing between sRNA and mRNA to activate or repress translation, and may recruit cellular endonucleases to degrade the transcript following repression.
To examine the RNA- and protein-binding properties of Hfq proteins in Escherichia coli, Listeria monocytogenes, and Caulobacter crescentus, I utilized a set of two transcription-based bacterial-hybrid assays designed to detect these interactions in vivo. In the bacterial two-hybrid assay (B2H), Hfq monomers from each bacterial species displayed inter- and intra-species multimerization, supporting the notion that hexamerization is a conserved feature of Hfq orthologs. Through the utilization of a novel bacterial three-hybrid assay designed to detect RNA-protein interactions in vivo, I report that the Hfq protein from each of these species is able to recognize a variety of sRNAs with unique binding patterns. A comparative analysis of the relative interaction strengths of Hfq from each of these species with a panel of E. coli sRNAs shows that the C. crescentus Hfq often displays stronger sRNA-binding interactions than E. coli Hfq and L. monocytogenes Hfq. Further analysis of these three proteins at the level of primary sequence and tertiary structure suggests that the presence of certain ionizable amino acid residues in the Hfq sequence may play particularly important roles in binding sRNAs across bacterial species.Biochemistr
The Blackhawks
No full textPhotograph - Hockey team members in uniform, Athabasca, Alberta. Left to right: C. Haufman (coach), George Grandbois, Gordon Lewis, Colin Preece, Charles Parker, David Jones, unknown, Ken Bissell, Archie Grandbois, unknow
- …
