1,721,016 research outputs found
Reproductive assurance weakens pollinator-mediated selection on flower size in an annual mixed-mating species
Full text linkBackground and Aims In animal-pollinated plants, direct and indirect selection for large and small flowers in predominantly outcrossing and selfing species, respectively, is a common consequence of pollen limitation (PL). However, many hermaphroditic species show a mixed-mating system known as delayed selfing, which provides reproductive assurance (RA) only when outcrossing is not realized. Although RA is expected to reduce pollinator-mediated selection towards larger flowers, the consequences of delayed selfing for selection on flower size in mixed-mating species remain overlooked. We investigated whether RA weakens selection on flower size in Tuberaria guttata, a mixed-mating annual herb. Methods We related pollinator visitation rates to flower size and measured seed production in emasculated, hand cross-pollinated and intact (control) flowers in three natural populations. For each population, we estimated variation in PL and RA across individuals differing in flower size and phenotypic selection on this trait. Key Results Pollinator visitation increased and RA decreased with flower size in all populations. Increasing RA diminished but did not fully alleviate PL, because of early-acting inbreeding depression. In the least-visited and most pollen-limited population, RA increased seed production by >200 %, intensely counteracting the strong pollinator-mediated selection for larger corollas. In the most-visited population, however, RA increased seed production by an average of only 9 %. This population exhibited the largest fraction of individuals that showed a decrease in seed production due to selfing and the weakest pollinator-mediated selection on flower size. Conclusions The results suggest that the balance between the extent of RA and outcrossing contributes to determine flower size in mixed-mating systems. Pollinator-mediated selection favours larger flowers by increasing outcrossed seeds, but the benefits of RA greatly lessen this effect, especially under severe conditions of pollen limitation. Our findings also indicate that a mixed-mating system can represent an ‘evolutionary trap’ under an adequate pollinator supply.Fil: López Teixido, Alberto. Universidad Rey Juan Carlos; EspañaFil: Aizen, Marcelo Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentin
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
Temperature-Limited Floral Longevity in the Large-Flowered Mediterranean Shrub Cistus Ladanifer (Cistaceae)
No full textManuscript received July 2014; revised manuscript received October 2014; electronically published December 19, 2014Premise of research. Larger and longer-lived flowers are more frequently pollinated, but they are associated with high maintenance costs due to greater water usage. The Mediterranean climate limits plant reproduction and maximizes resource use efficiency, so smaller and short-lived flowers are potentially advantageous under hot and dry conditions.Methodology. We experimentally evaluated the relationship between the floral longevity of Cistus ladanifer, a large-flowered Mediterranean shrub, and pollination, flower size, and temperature at two different altitudes with contrasting climatic conditions. We hypothesized that flower size and longevity would be reduced in the drier and hotter conditions of the lower-altitude site. In addition, we expected that floral longevity would decrease with experimental pollen deposition, flower size, and temperature. We pollinated and capped flowers to evaluate the variation in floral longevity by comparing actual and potential floral longevity at low and high altitudes.Pivotal results. In agreement with our hypothesis, flower size was observed to increase with altitude, but, contrary to expectations, floral longevity decreased at the high altitude since temperature increased during the flowering time. Floral longevity tended to be short but depended on pollination, such that potential floral longevity was greater than actual floral longevity. Capped flowers lasted longer (1.31 ± 0.65 d) than control (0.95 ± 0.39 d) or hand-pollinated (0.60 ± 0.08 d) flowers. At the high altitude, larger flowers and higher temperatures resulted in a reduction in both the observed and potential floral longevity, but temperature had a differential effect in limiting potential floral longevity.Conclusions. Our experimental survey reported short-lived flowers and limitations in floral longevity when flowers were larger and temperatures were higher. Overall, the results reveal an important effect of temperature on increasing floral maintenance costs, imposing selective pressures on flower size, and longevity in large-flowered Mediterranean plants.This study was supported by the REMEDINAL project (S-0505/AMB/000355) of Comunidad de Madrid, Spain, and by the CONSOLIDERMONTES project (CSD2008-00040) of the Spanish Ministerio de Ciencia e Innovación.Peer reviewe
Impacts of changes in land use and fragmentation patterns on Atlantic coastal forests in northern Spain
No full textAcknowledgements
We would like to thank Luis Costa and the forest rangers of Fragas do Eume Natural Park for fieldwork support. We are also grateful to Rosa Menéndez for providing comments, Tatiana Izquierdo for helping with GIS and Lori J. De Hond for linguistic assistance. This research was supported by the Galician Consellería de Medio Ambiente e Desenvolvemento Sostible (project 215/2006) and by the Spanish Ministerio de Educación y Ciencia (project CGL2006-07012). FOGGA (Fondo Galego de Garantía Agraria) provided the orthoimages used in the study.Changes in forested landscapes may have important consequences for ecosystem services and biodiversity conservation. In northern Spain, major changes in land use occurred during the second half of the 20th century, but their impacts on forests have not been quantified. We evaluated the dynamics of landscape and forest distribution patterns between 1957 and 2003 in Fragas do Eume Natural Park (northwestern Spain). We used orthoimages and a set of standard landscape metrics to determine transitions between land cover classes and to examine forest distribution patterns. Eucalypt plantations showed the greatest increase in area (197%) over time. Furthermore, transitions to eucalypt plantations were found in all major land cover classes. Forest showed a net decline of 20% in total area and represented 30% of the landscape area in 2003. Forest losses were mainly due to eucalypt plantations and the building of a water reservoir, while forest gains were due to increases in shrubland, meadows and cultivated fields which had been recolonised. Forest patch size and core area decreased, and edge length increased over time. In turn, increases were obtained in mean distance between forest patches, and in adjacency to eucalypt plantations and to a water reservoir. These results suggest an increase in forest fragmentation from 1957 to 2003, as well as a change in the nature of the habitat surrounding forest patches. This study shows that land use changes, mostly from eucalypt plantation intensification, negatively affected forested habitats, although some regeneration was ongoing through ecological succession from land abandonment.Ministerio de Educación y Ciencia (España)Xunta de GaliciaDepto. de Biodiversidad, Ecología y EvoluciónFac. de Ciencias BiológicasTRUEpu
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
Disproportionate carbon and water maintenance costs of large corollas in hot Mediterranean ecosystems
No full textLarger corollas increase the reproductive success of entomophilous plants, but are also associated with increased carbon and water costs, especially under hot and dry conditions. Minimizing floral carbon and water loss by reducing corolla size should be potentially advantageous for plants living in these environments. We quantify maintenance costs of corollas (water and carbon) in large-flowered rockroses (Cistus spp.) in a Mediterranean ecosystem. We performed field studies of two coflowering sympatric Cistus of contrasting corolla size to analyze water costs. Additionally, we used the larger-flowered species (C. ladanifer) to analyze the effects of intraspecific variation in corolla size on floral net carbon exchange and transpiration rates. We also assessed the mean daily percentage of plant water and carbon consumed by corollas by comparing with that of leaves at the time of flowering in C. ladanifer. Temperature and corolla area increased water maintenance costs, following an allometric relationship where transpiration rate per unit of area increased with corolla area. Larger flowers tended to heat less under strong irradiance than smaller ones in both species, especially in C. ladanifer, demonstrating a stronger transpirational cooling effect on larger flowers. In terms of carbon, temperature significantly affected net carbon exchange rates, which were not affected by corolla size. Daily water and carbon expenses of corolla were ca. 50% of those of leaves on an organ surface area basis. Our results suggest that water and carbon maintenance costs of large flowers in the Mediterranean impose significant constraints to corolla size, ecophysiologically favoring smaller-flowered individuals in these ecosystems. © 2014 Geobotanisches Institut ETH, Stiftung Ruebel.This study was supported by the REMEDINAL project (S-0505/AMB/000355) of Comunidad de Madrid, Spain, and by CONSOLIDER MONTES project (CSD2008-00040) of the Spanish Ministerio de Ciencia e Innovación.Peer Reviewe
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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