1,720,987 research outputs found
Development of a trophic model of the ecosystem of Macrocystis pyrifera on Natividad Island.
No full textActualmente, los ecosistemas marinos están sujetos a cambios antropogénicos y ambientales que afectan su estructura y función. Las pesquerías, es una de las principales perturbaciones antropogénicos a la que están sujetos los ecosistemas globalmente. La principal repercusión de la pesquería sobre los ecosistemas es una fuerte disminución de la biomasa y densidad de algunas de sus especies que incluso pueden llegar a desaparecer. Los modelos ecosistémicos, basados en datos de monitoreo para diseñar experimentos, es una alternativa que ayuda a entender la estructura y funcionamiento de las comunidades naturales y a diseñar mejores medidas de manejo y conservación. El objetivo de este trabajo es conocer la estructura del ecosistema de sargazo gigante de Isla Natividad en la costa del Pacífico de Baja California y evaluar diferentes escenarios de mortalidad por pesca que puedan afectar al ecosistema en general y a los grupos funcionales que lo forman. Para conocer la estructura del ecosistema de sargazo gigante de Isla Natividad se generó un modelo Ecopath con Ecosim, utilizando datos de monitoreos. Se clasificaron 40 grupos funcionales incluyendo vertebrados, invertebrados y detritos. Los valores de biomasa se obtuvieron de un gran esfuerzo de monitoreos in situ y los valores de producción/biomasa y consumo de biomasa se obtuvieron de una intensa búsqueda bibliográfica. Se generaron 9 escenarios para predecir cómo va a responder el ecosistema a cambios en la mortalidad por pesca y en el tiempo; se combinaron predicciones temporales (10, 20 y 30 años) y cambios porcentuales de mortalidad por pesca (aumento 10%, disminución 10% y constante). Se desarrolló el modelo satisfactoriamente lo que permitió conocer la estructura del ecosistema de Isla Natividad, así como las interacciones entre los grupos funcionales y las flotas pesqueras. Todos los escenarios predictivos muestran una disminución total de biomasa en el ecosistema. Sin embargo, no todos los grupos funcionales responden de la misma forma ya que el aumento de la pesquería favorece al aumento de la biomasa de algunos, pero no de otros. Además, la biomasa total del ecosistema se ve directamente afectada por la biomasa del alga estructuradora Macrocystis pyrifera, cuya presencia hace que el ecosistema pierda menor biomasa a pesar del aumento de la mortalidad por pesca.Marine ecosystems are subject to anthropogenic and environmental changes affecting both their structure and function. Fisheries entail one of the major anthropogenic disturbances to many ecosystems on a global scale. Many fished marine ecosystems show trending reductions in biomass and density, resulting in the disappearance of some species over time. The construction of ecosystem models using monitoring data allows for the exploration of the structure and function of ecosystems under different scenarios, allowing for the improved design of management and conservation tools. In this study, I determined the structure of the macroalgal ecosystem of Isla Natividad, Baja California Sur, Mexico, under different fishing mortality scenarios using an Ecopath model with Ecosim model based on in situ monitoring data. Forty functional groups were classified, including vertebrates, invertebrates and detritus. Biomass values were obtained from a large in situ monitoring effort; and the values of production / biomass and biomass consumption were obtained from the literature. To predict how the ecosystem would respond to changes in fishing mortality and over time, 9 scenarios were generated, or to 10, 20 and 30 years, under present fishing mortality, a 10% increase and a 10% decrease. Under all predicted scenarios, the ecosystem model showed a decline in total biomass. Not all functional groups responded in the same way as the biomass of some groups was favored by increased fishing mortality but not others. In addition, the total biomass of the ecosystem was directly affected by the biomass of the structural alga Macrocystis pyrifera, whose presence appears to buffer the ecosystem against biomass loss. This study highlights the importance of looking at functional groups of the ecosystem separately, as they can respond quite differently under the same scenario
Population dynamics of the purple sea urchin (Strongylocentrotus purpuratus) in the thershold between a kelp bed and an urchin barren in the Baja California peninsula.
No full textEl erizo morado (Strongylocentrotus purpuratus) se ha definido como una especie que estructura las comunidades algales de la península de Baja California siendo el principal pastoreador de los bosques de sargazo gigante de Macrocystis pyrifera. El efecto del erizo en los bosques de sargazo varía en respuesta a la disponibilidad de alimento, a las condiciones ambientales y las interacciones ínterespecificas. Para evaluar las características poblacionales del erizo morado, se llevo a cabo un muestreo submareal a ~20 m de profundidad donde existe la convergencia entre los mantos de sargazo gigante de Macrocystis pyrifera y los desierto de erizos. Se compararon 4 sitios de muestreo: Islas Todos Santos y Campo Kennedy localizados en el norte de la península, sujetos a presión pesquera, Isla Natividad y Bahía Tortugas localizados en el sur (cerca del límite sur de distribución tanto para S. purpuratus como para M. pyrifera y sin esfuerzo pesquero). Se colectaron datos de densidad poblacional, diámetro de la testa (mm) e índice gonádico del erizo y densidad de frondas por planta de M. pyrifera, para comparar la estructura poblacional del erizo y su asociación con los mantos de sargazo en invierno del 2003 y primavera del 2004. Los resultados muestran que la variación de las características poblacionales del erizo se encuentra altamente correlacionada con las características poblacionales de los mantos (mayor densidad e índice gonádico del erizo se asocian con mayor cantidad de alimento disponible). No se pudo identificar el efecto del erizo sobre los mantos (densidad de plantas homogénea desde el borde al centro del manto), posiblemente debido a que la pesquería está regulando las poblaciones del erizo y controlando el sobre pastoreo. Se recomienda seguir estudiando este sistema para recopilar mayores observaciones sobre la dinámica entre estos dos estados alternos y poder proponer una regulación exitosa para mantener estos recursos.It has been defined that the Purple sea urchin (Strongylocentrotus purpuratus) is the principal grazer that structure the algal communities off the coast of the Baja California Peninsula. The effect of the sea urchins on the kelp beds variates in response of its food availability, environmental conditions and interspecific interactions. In order to evaluate the purple sea urchin population characteristics we conducted subtidal population structure surveys at ~20 m depth where an urchin barren and a kelp bed existed (where urchin harvest effort is direct). We compared 4 sites: Isla Todos Santos and Campo Kennedy in the north (highly fished), and Isla Natividad and Bahía Tortugas in the south (protected areas). Bahía Tortugas is also the southern limit of the range for purple urchins as well as for Macrocystis pyrifera (its favorite feeding resource). We sampled urchin population density, test diameter (mm) and gonad index, as well as kelp density and fronds per plants to compare the sea urchin population structure and its association with kelp beds along the Baja peninsula in winter 2003 and spring 2004. The result showed that the sea urchin and kelp beds population characteristics are highly correlated (higher sea urchin density and gonad index are related with higher food availability concentration).The sea urchin effect on the kelp bed couldn’t be identify because the density distribution of the sea urchin a cross the border between the kelp bed and the urchin barren was homogenous, maybe due to the over grassing control by the fisheries. Nonetheless it’s recommended to keep studying this system to compile major observations about the dynamics within this two stable states of the community in order to propose a successful regulation to maintain these resources
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
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