1,721,029 research outputs found
Geographical variation in the distributional constraints along a gradient of population aggregation
No full textFactors determining species distributions have frequently been shown to vary geographically, yielding spatially variable species–environment relationships when developing species distribution models. Using occurrence data for four bird species, we analysed to what extent position within the distribution range along a gradient of population aggregation determined geographical variation of distributional constraints. We built generalised linear models for the whole dataset (global models) and separately for each region within the species range with decreasing population aggregation (core, middle and peripheral). For both global and regional models, we compared species responses to habitat conditions showing an overall higher model fit in peripheral regions than in middle and core regions. Better model fit in peripheral regions was also found after including a spatial factor (i.e. an autocovariate estimating the proportion between the presences and total observations within a 10 km radius) into the global and regional models.The scattered availability of suitable habitat patches in a predominantly hostile landscape matrix seems to be the limiting factor for species distributions in peripheral regions. Conversely, the larger number of spatially dependent occurrences in core and middle region may favour source and sink population dynamics, yielding poorer relationships between habitat conditions and species occurrence. The role of the spatial factor after removing the co-variation with habitat conditions separately for each region suggests that endogenous processes such as dispersal vary throughout the species range but differently for each species. Geographical variation in distributional constraints can be interpreted as a consequence of the inherent spatial character of ecological processes and their interaction with varying environmental conditions throughout the species range. Overlooking the effects of spatial variation in distributional constraints may lead to erroneous management conclusions and inadequate estimation of the species’ response to environmental changes.<br/
Does fire increase the seasonal variability of bird communities ? A case in Mediterranean shrublands
No full textFire, a frequent phenomenon in Mediterranean landscapes, is a major ecological disturbance in terrestrial ecosystems. We hypothesized that bird communities undergo greater seasonal changes in burnt areas than in unbumt ones. Using the point-count method we assessed bird species composition and abundance in three zones (unbumt, burnt in 1982, and burnt in 1994) during the breeding and wintering seasons of 1997 and 1998.
From the breeding to the wintering seasons, burnt zones showed an increase in forest species, whereas the bird community of the unbumt zone remained stable in the gradient open-forest species. Moreover, the seasonal turnover of communities was higher in burnt zones than in the unbumt ones, although this did not imply that the former varied in richness through the year. The pattern of bird abundance in the unbumt zone was similar during the two study years, in contrast with that of burnt zones, suggesting higher annual cyclicity in resource availability in unbumt areas. These findings suggest that fire increases the seasonal variability of bird communities.Les incendies, phénomènes habituels dans les paysages méditerranéens, sont l’une des principales perturbations écologiques des systèmes terrestres. On a cherché à vérifier l’hypothèse selon laquelle les variations saisonnières des communautés d’oiseaux augmenteraient dans les zones brûlées. En utilisant la méthode des points d’écoute pendant la période de nidification et l’hiver 1997 et 1998, on a déterminé la composition et l’abondance de ces communautés dans trois zones (non-brûlée, brûlée en 1982 et brûlée en 1994).
Entre ces deux saisons, les zones incendiées ont montré un accroissement du nombre d’espèces forestières, tandis que dans la zone intacte la communauté est restée stable le long du gradient forêt-milieux ouverts. De plus, le turn-over saisonnier fut supérieur dans les zones brûlées sans que ceci implique une variation de la richesse spécifique au long de l’année. Contrairement aux zones brûlées, les parties intactes n’ont pas montré de grandes fluctuations d’abondance des espèces, ce qui y suggère une plus forte cyclicité annuelle de la disponibilité des ressources. Ces résultats indiquent que le feu augmenterait la variabilité saisonnière des communautés d’oiseaux.Herrando Sergi, Brotons Lluis, Llacuna Santiago. Does fire increase the seasonal variability of bird communities ? A case in Mediterranean shrublands. In: Revue d'Écologie (La Terre et La Vie), tome 57, n°2, 2002. pp. 151-163
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
