1,720,971 research outputs found
Patterns of plant invasions in China: Taxonomic, biogeographic, climatic approaches and anthropogenic effects
No full textFast life history traits promote invasion success in amphibians and reptiles
Get PDFCompeting theoretical models make different predictions on which life history strategies facilitate growth of small populations. While ‘fast’ strategies allow for rapid increase in population size and limit vulnerability to stochastic events, ‘slow’ strategies and bet-hedging may reduce variance in vital rates in response to stochasticity. We test these predictions using biological invasions since founder alien populations start small, compiling the largest dataset yet of global herpetological introductions and life history traits. Using state-of-the-art phylogenetic comparative methods, we show that successful invaders have fast traits, such as large and frequent clutches, at both establishment and spread stages. These results, together with recent findings in mammals and plants, support ‘fast advantage’ models and the importance of high potential population growth rate. Conversely, successful alien birds are bet-hedgers. We propose that transient population dynamics and differences in longevity and behavioural flexibility can help reconcile apparently contrasting results across terrestrial vertebrate classes
Local canopy disturbance as an explanation for long‐term increases in liana abundance
Get PDFEnvironmental Biolog
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
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Understory Plant Community Responses to Post-fire Environments in the Sierra Nevada
Get PDFForests in the North American Mediterranean Climate zone (NAMCZ) are increasingly defined by novel disturbance regimes and manifestations of climate change. Many regions in the NACMZ, including the yellow pine/mixed-conifer (YPMC) forests of the Sierra Nevada, California, that historically experienced low to moderate intensity fire regimes are seeing increased area burned at high intensity resulting in high post-fire severity as a result of interactions between high fuel loads and climate warming with a number of negative ecological effects. It is important to understand species responses to the ecological disturbance of wildfire in this context, especially from the perspective of the understory plant community where the bulk of regional plant diversity is found and vital ecosystem functions take place. We examined understory plant responses across gradients of post-wildfire severity, shrub cover and a suite of other post-fire environmental features in over 400 plots of YPMC forests of the Sierra Nevada. We found a generally unimodal ‘hump-shaped’ relationship between local (alpha) understory plant diversity and fire severity. High severity burning resulted in lower local diversity and there was some indication of homogenization of the flora at the regional scale. Fire severity class, postfire litter cover, and annual precipitation were the best predictors of understory species diversity. In the YPMC forests of the NAMCZ, shrub lifeforms tend to be promoted by high intensity fires, and the recent increase in the extent of high intensity burning is driving major changes in the spatial patterns of shrub-dominated vegetation. We further examined understory plant community response to shrub cover and demonstrated that understory plant species diversity and evenness decline as shrub cover increased while understory richness was less affected. We used structural equation modeling to better understand relationships among shrub cover, understory richness and diversity and other environmental variables. Our examinations of specific lifeforms and life history categories in the understory revealed that while many environmental factors influence richness, water availability, rock and shrub cover mostly determine diversity and evenness. Our research suggests that increases in post-fire severity in systems historically characterized by low to moderate intensity wildfire may lead to understory plant diversity losses. Anticipated increases in shrubfield area due to these changing wildfire regimes will also likely negatively impact native herbaceous plant species diversity. These findings collectively indicate that global patterns of increasing fire size and severity may have important implications for regional plant species biodiversity
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
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