1,721,030 research outputs found
Comparative germination ecology of the endemic Centranthus amazonum (Valerianaceae) and its widespread congener Centranthus ruber
No full textCentranthus amazonum Fridl. & A. Raynal (Valerianaceae) is a critically endangered
narrow endemic to Central–Eastern Sardinia (Italy), where it occurs in rocky habitats. In
the present study, the germination ecology of this species was investigated and compared
with the relatively widespread species Centranthus ruber (L.) DC. subsp. ruber. In particular,
the effects of a range of constant temperatures (5–25°C) and two alternating
temperature regimes (25/10 and 30/15°C) on seed germination were analyzed. For the two
species, cardinal temperatures were determined as the reciprocal of time to 50% germination
(t50). In addition, seed persistence in the soil was assessed by experimental seed
burials. Seeds of both species were non-dormant; however, C. amazonum produced more
empty seeds and germination was slower and reached lower final percentages than C.
ruber. Moreover, seed and seedling mass of C. ruber were higher than for C. amazonum
and the lack of a persistent soil seed bank detected for C. amazonum increases vulnerability
to extinction for this species. The present study provides new data on the germination
ecology of the previously unstudied C. amazonum that may explain the rarity of
this species when compared with the commonness of C. ruber
Effects of temperature, light and pre-chilling on germination of Rhamnus persicifolia, an endemic tree species of Sardinia(Italy)
No full textRhamnus persicifolia is an endemic small tree or shrub belonging to the R. cathartica group. It grows along
mountainous waterways of the Central-Eastern Sardinia (Italy). The purpose of this study was to report the effects
of temperature, light and pre-chilling on germination of R. persicifolia seeds. The applied treatments included
a range of constant temperatures (5-30°C) and two alternating temperature regimes (15/5 and 25/10°C), with
two photoperiods (8 h light / day and darkness). In addition, the most effective germination temperature (25°C)
was repeated including a pre-chilling period (5°C for 3 months). R. persicifolia reached maximum germination
percentages (> 70%) at warm temperatures (≥ 20°C), with no differences between constant and alternating
regimes and no response to light. While the pre-chilling period did not increase germination percentage it had
a positive effect on germination rate, reducing T50 by more than 50%. These studies provide new information
on the seed biology of this endemic species and enable ex situ seed germination, which may prove useful for
habitat restoration activities
Ecological and morphological seed traits of Polygala sardoa and P. sinisica: A comparative study on two endemic species of Sardinia
No full textPolygala sardoa Chodat and P. sinisica Arrigoni (Polygalaceae) are two exclusive endemics to Sardinia
and P. sinisica is affiliated under “Critically Endangered” in the IUCN Red Lists. In this work comparative
studies on two populations of P. sardoa and in the only one of P. sinisica were carried out. In particular,
seed output calculations and morphometric measurements on seed and elaiosome sizes were carried
out. The effect of chipping, constant (15 ◦C) and alternating (25/10 ◦C) temperature regimes and light (8 h
irradiance/day and dark) on germination were investigated. Seedling vigor assessments and a study on
seed persistence in the soil were also carried out. P. sinisica had a higher seed output than P. sardoa and P.
sinisica seeds were smaller than those of P. sardoa, with lower elaiosome area and elaiosome ratio values.
Neither species had alternating temperature or light requirements for germination. P. sardoa achieved
high germination percentages (> 80%) at all the tested conditions. P. sinisica had a lower maximum germination
(<60%), suggesting the presence of physiological dormancy, and took more than twice as long to
reach the maximum germination percentage. Seedlings of P. sardoa were larger than those of P. sinisica,
and neither species formed a persistent soil seed bank. These new data may help implement effective
conservation measures for these two species and, more generally, for threatened endemic species of this
genus
Germination requirements of the alpine endemic Silene elisabethae Jan: effects of cold stratification, light and GA3
No full text
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
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