1,720,955 research outputs found
Abundance, niche breadth, and niche occupation of Central European tree species in the centre and at the margin of their distribution range
No full textHow abundance, niche breadth and niche occupation of species change within the distribution range remains unresolved for tree floras. We compared populations of three common and three rare European tree species in the distribution centre and at the eastern margin with respect to abundance, niche breadth, and preferential occurrence along several soil-related niche axes. We hypothesised that: (i) abundance is higher, and niche breadth greater, in the distribution centre than at the margin, (ii) that the occupied niche differs between central and marginal populations with species being restricted to more favourable soils at the margin, and (iii) that common and rare species show different patterns. We characterised the occupied niche and niche breadth in a semi-quantitative way and discuss the role of human impact on tree abundance in the light of evidence from paleoecology and forest dynamics research. Five of the six species are more abundant in the centre than at the margin, at least in the natural vegetation prior to human intervention. In contrast to soil niche breadth, the preference for soil chemical and hydrological properties differed between centre and margin. Contrary to expectation, a shift to less fertile and partly also drier sites at the margin was observed, although bedrocks which give rise to the development of fertile soils were more frequent in Slovakia (ca. 49% of the total area compared to 20% in Central Germany) and bedrock types which produce infertile soils were more abundant in Central Germany (about 23% vs. 2% in Slovakia). While the abundant-centre-distribution hypothesis is supported by our data, we found no conclusive evidence of competitive displacement of weaker competitors and of a niche shift of superior competitors to more favourable sites at the range margin. Factors other than competition must be responsible for the observed niche shifts. Higher drought stress does not seem to be a limiting factor at the eastern margin, where dry sites were occupied more frequently compared to the centre. (C) 2009 Elsevier B.V. All rights reserved.Helmholtz Association of National Research Centre
The relationships between abundance, range size and niche breadth in Central European tree species
No full textRange size and niche breadth have been found to be positively related to abundance in many plant and animal groups. We tested these two relationships for the tree species flora of Central Europe; that is, for all 25 species that have their distribution centre in this region. Eurasia, with a focus on Central Europe. We devised an abundance and niche variable classification system to transform the existing literature data into a semi-quantitative assessment of abundance and niche breadth (in terms of soil chemical and physical variables, and temperature) for each of the 25 tree species. Regression analyses between abundance, range size and niche breadth were conducted for the entire species sample and for subsets of species defined by their ecology or phylogeny. The relationship between abundance in the distribution centre and range size was weak for the Central European tree species. However, significant abundance-range size relationships were found for phylogenetically or ecologically more homogenous species groups (for example for trees of the order Rosales and for mid-successional tree species). Realized niche breadth was positively related to range size in the case of temperature, but not for soil-related variables. No relationship existed between niche breadth and abundance in the distribution centre. We hypothesize that the weak relationship between abundance and range size is primarily a consequence of substantial ecological and phylogenetic heterogeneity within this rather species-poor assemblage. The positive relationship between realized temperature niche breadth and range size emphasizes the strong influence of climatic variables on plant distribution patterns over continental or global scales
Are marginal beech (Fagus sylvatica L.) provenances a source for drought tolerant ecotypes?
No full textDue to the expected increases of number and intensity of summer droughts in Central Europe the identification of drought tolerant ecotypes becomes more important in future forestry. A common garden experiment with seedlings of Fagus sylvatica provenances from the center (Germany) and eastern margin (Poland) of the species' distribution range was conducted. Responses of morphological, physiological, chemical and growth parameters to three drought treatments were analyzed. Relative growth rates of the marginal provenance were lower as compared to the central provenance. The marginal seedlings showed a tendency to higher total biomasses because of higher seed masses. In both provenances drought decreased biomass production and root/shoot ratio which was lower in the central provenance. A lower specific root area of the marginal provenance indicated a better adaptation to low xylem water potentials. Under moderate drought, lower leaf delta(13)C signatures may indicate lower stomatal limitation (or a reduced rate of CO(2) assimilation) in the marginal provenance. We conclude that marginal beech provenances may exhibit a better drought adaptation.Helmholtz-Gemeinschaft (HGF
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
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
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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