1,720,976 research outputs found
Los herbívoros como agentes selectivos sobre atributos de valor funcional en ambientes de sombra.
No full textTesis presentada para optar al grado de Doctor/a en Ciencias Biológicas con mención en Botánica.La disponibilidad de luz puede limitar el establecimiento de las plantas en un hábitat determinado. El nivel de tolerancia de las plantas a la sombra es el resultado de la expresión fenotípica de atributos funcionales que les permiten mantener un balance de carbono positivo en ambientes de baja luz. Sin embargo, se ha sugerido que variantes de algunos atributos funcionales relevantes para la sombratolerancia están relacionadas con un aumento en el riesgo de sufrir herbivoría. Adicionalmente, las respuestas contra los herbívoros pueden interferir con las respuestas de la planta a la sombra. Tanto la interferencia entre respuestas como los costos asociados a mayor herbivoría pueden limitar la expresión de un fenotipo “óptimo” que tenga un alto desempeño en sombra. En consecuencia, los herbívoros podrían jugar un papel relevante en los niveles de sombratolerancia expresados por las plantas. A través de una combinación de experimentos de campo e invernadero, esta tesis pone prueba dicha hipótesis a tres escalas distintas: individual, intraespecífica e interespecífica. Esta aproximación reflejará procesos de adaptación a la sombra a distintos niveles: respuestas del individuo, selección fenotípica y evolución. Los resultados motrarón que la herbivoría disminuye la supervivencia de plántulas de las especies demandantes de luz Aristotelia chilensis y Embothrium coccineum, pero sólo en la sombra, mostrando que los herbívoros pueden estar limitando el establecimiento de plantas demandantes de luz en el sotobosque. A escala individual la herbivoría modifica las respuestas funcionales a la sombra en plántulas de A. chilensis. Tales modificaciones pueden comprometer ganancia de carbono del individuo, lo que podría explicar el gran deterioro de la adecuación biológica en la sombra luego de la herbivoría. Los análisis de selección fenotípica en A. chilensis mostraron que el ambiente lumínico es la principal fuerza selectiva actuando sobre la fotosíntesis (Amax), el área foliar específica (SLA) y las tasas de crecimiento relativo (RGR). Mientras que en el sol, la selección favorece a individuos con valores altos de Amax y RGR, en sombra encontramos evidencia de selección estabilizadora para RGR y direccional positiva para SLA. Más relacionado con nuestra hipótesis, se halló evidencia de que los herbívoros son capaces de cambiar el patrón de selección de SLA en ambientes de sombra, demostrando que los enemigos naturales son agentes de selección actuando sobre este atributo. Adicionalmente, a escala interespecífica, atributos funcionales relacionados con la sombratolerancia -SLA, razón de área foliar (LAR) y respiración oscura (Rdmass)- y RGR estuvieron relacionados positivamente con el porcentaje de herbivoría sufrido por las especie. A escala interespecífica, los patrones de correlaciones entre atributos funcionales a la sombra y los niveles de herbivoría, sugieren que la evolución de la sombratolerancia en plantas está asociada a la expresión de atributos que les permitan retener los recursos e impedir el daño causado por los herbívoros, como por ejemplo bajos valores de SLA –relacionados con alta inversión en reforzamiento estructural de la hoja- y RGR. En conjunto estos resultados apoyan la idea de que los herbívoros pueden ser una fuerza importante definiendo los niveles de tolerancia a la sombra de las plantas, debido a la interrelación que existe entre atributos funcionales y herbivoría.Facultad de Ciencias Naturales y OceanográficasDepartamento de BotánicaConcepció
Data from: Herbivores modify selection on plant functional traits in a temperate rainforest understory
No full textThere is limited evidence regarding the adaptive value of plant functional traits in contrasting light environments. It has been suggested that changes in these traits in response to light availability can increase herbivore susceptibility. We tested the adaptive value of plant functional traits linked with carbon gain in contrasting light environments and also evaluated whether herbivores can modify selection on these traits in each light environment. In a temperate rainforest, we examined phenotypic selection on functional traits in seedlings of the pioneer tree Aristotelia chilensis growing in sun (canopy gap) and shade (forest understory) and subjected to either natural herbivory or herbivore exclusion. We found differential selection on functional traits depending on light environment. In sun, there was positive directional selection on photosynthetic rate and relative growth rate (RGR), indicating that selection favors competitive ability in a high-resource environment. Seedlings with high specific leaf area (SLA) and intermediate RGR were selected in shade, suggesting that light capture and conservative resource use are favored in the understory. Herbivores reduced the strength of positive directional selection acting on SLA in shade. We provide the first demonstration that natural herbivory rates can change the strength of selection on plant ecophysiological traits, that is, attributes whose main function is resource uptake. Research addressing the evolution of shade tolerance should incorporate the selective role of herbivores
Herbivory on temperate rainforest seedlings in sun and shade: resistance, tolerance and habitat distribution.
No full textDifferential herbivory and/or differential plant resistance or tolerance in sun and shade environments may influence plant distribution along the light gradient. Embothrium coccineum is one of the few light-demanding tree species in the temperate rainforest of southern South America, and seedlings are frequently attacked by insects and snails. Herbivory may contribute to the exclusion of E. coccineum from the shade if 1) herbivory pressure is greater in the shade, which in turn can result from shade plants being less resistant or from habitat preferences of herbivores, and/or 2) consequences of damage are more detrimental in the shade, i.e., shade plants are less tolerant. We tested this in a field study with naturally established seedlings in treefall gaps (sun) and forest understory (shade) in a temperate rainforest of southern Chile. Seedlings growing in the sun sustained nearly 40% more herbivore damage and displayed half of the specific leaf area than those growing in the shade. A palatability test showed that a generalist snail consumed ten times more leaf area when fed on shade leaves compared to sun leaves, i.e., plant resistance was greater in sun-grown seedlings. Herbivore abundance (total biomass) was two-fold greater in treefall gaps compared to the forest understory. Undamaged seedlings survived better and showed a slightly higher growth rate in the sun. Whereas simulated herbivory in the shade decreased seedling survival and growth by 34% and 19%, respectively, damaged and undamaged seedlings showed similar survival and growth in the sun. Leaf tissue lost to herbivores in the shade appears to be too expensive to replace under the limiting light conditions of forest understory. Following evaluations of herbivore abundance and plant resistance and tolerance in contrasting light environments, we have shown how herbivory on a light-demanding tree species may contribute to its exclusion from shade sites. Thus, in the shaded forest understory, where the seedlings of some tree species are close to their physiological tolerance limit, herbivory could play an important role in plant establishment
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
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