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Search Results: 1 - 10 of 27831 matches for " MARIO GEORGE-NASCIMENTO "
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Una evaluación de los índices bibliométricos I e Is de Molina-Montenegro & Gianoli aplicada a investigadores en ciencias ecológicas en Chile
GEORGE-NASCIMENTO,MARIO;
Revista chilena de historia natural , 2010, DOI: 10.4067/S0716-078X2010000200003
Abstract: the interest in measuring the scientific output has led to an increasing number of indices being proposed. in this commentary i critically examine the indices i and is proposed by molina-montenegro & gianoli (2010; in this issue), and the criteria employed by these authors to incorporate or exclude scientists from their database of chilean researchers in ecology. i also assess the statistical relationship between the indices of scientific output i, is and hirsch's h, and the primary variables that compose them. to do that i use correlation and linear regression analyses. results show that the i index is highly associated to the number of co-authors, and keeps a high positive and significant correlation with the h index, after adjusting by log10 of the number of alocitations and the number of self-citations. this suggests that the number of co-authors and self-citations are not important predictors of the differences between h and i. in contrast, the is index decreases with scientific age, which would be an undesirable outcome, and a result of dividing the i index by the scientific age. i suggest that inspecting residuals of the regression between the log10 of the number of alocitations and the scientific age is a simple and straightforward way to assess whether a scientist should be promoted, hired or awarded.
Una evaluación de los índices bibliométricos I e Is de Molina-Montenegro & Gianoli aplicada a investigadores en ciencias ecológicas en Chile An assessment of the bibliometric indices I and Is of Molina-Montenegro & Gianoli applied to researchers in ecological sciences in Chile
MARIO GEORGE-NASCIMENTO
Revista chilena de historia natural , 2010,
Abstract: El interés por medir la producción científica ha originado un creciente número de índices. En este comentario examino críticamente los índices I e Is propuestos por Molina-Montenegro & Gianoli (2010; en este número), y los criterios empleados por estos autores para incorporar o excluir a científicos de su base de datos de investigadores chilenos en ecología. Además analizo la relación estadística entre los índices de producción científica I, Is y h de Hirsch, y las variables que los componen. Para ello empleo análisis de correlación y de regresión lineal. Los resultados muestran que luego de la corrección por el número de coautores y de autocitas que incorpora el índice I, este está principalmente asociado al log10 del número de alocitas, y mantiene una alta correlación con el índice h. Esto sugiere que el número de coautores y de autocitas no son predictores importantes de las diferencias entre ambos índices. En cambio, el índice Is es el único que disminuye con la edad científica, lo que se considera un efecto indeseable, y resultante de corregir mediante la división del valor del índice I por la edad científica. Al examinar los residuos de la regresión entre el log10 del número de alocitas y la edad científica se distingue nítidamente a quiénes habría que promover, contratar o premiar, lo que constituye una manera más simple y directa de evaluar comparativamente la producción de un investigador. The interest in measuring the scientific output has led to an increasing number of indices being proposed. In this commentary I critically examine the indices I and Is proposed by Molina-Montenegro & Gianoli (2010; in this issue), and the criteria employed by these authors to incorporate or exclude scientists from their database of Chilean researchers in ecology. I also assess the statistical relationship between the indices of scientific output I, Is and Hirsch's h, and the primary variables that compose them. To do that I use correlation and linear regression analyses. Results show that the I index is highly associated to the number of co-authors, and keeps a high positive and significant correlation with the h index, after adjusting by log10 of the number of alocitations and the number of self-citations. This suggests that the number of co-authors and self-citations are not important predictors of the differences between h and I. In contrast, the Is index decreases with scientific age, which would be an undesirable outcome, and a result of dividing the I index by the scientific age. I suggest that inspecting residuals of the regression between the log10 of
Efectos del rizocéfalo Loxothylacus armatus (Cirripedia: Rhizocephala) en el cangrejo Paraxanthus barbiger (Decapoda: Brachyura) en Chile
GEORGE-NASCIMENTO,MARIO; BUSTOS,JOSé;
Revista chilena de historia natural , 2006, DOI: 10.4067/S0716-078X2006000200001
Abstract: in the marine realm, several biological associations are distributed worldwide and are highly specific, but remain poorly studied in chile. here, we describe quantitatively the infection by the barnacle loxothylacus armatus boschma 1949 (cirripedia: rhizocephala) in the crab paraxanthus barbiger (poeppig 1836) (decapoda: brachyura), and assess if the parasite effects are similar to rhizocephalan-decapod associations elsewhere. to do this, 513 crabs were collected by hand while scuba diving between september and october, 2003 in the shallow subtidal zone of lenga (37° s), chile. maximum prevalence reached ca. 60 % in small body size hosts, producing total castration of males, inhibiting the gonadic development of female crabs and modifying the size of sexual characters in both sexes, thus revealing that this parasite imposes a great demand upon its host. these results are closely similar to others involving rhizocephalans, and suggest that taking into account symbiosis like this one in the study of benthic communities in chile could lead to new interpretations about the abundance and reproductive patterns of p. barbiger, which is a prominent predator in these communities
Pseudoterranova cattani sp. nov. (Ascaridoidea: Anisakidae), a parasite of the South American sea lion Otaria byronia De Blainville from Chile
GEORGE-NASCIMENTO,MARIO; URRUTIA,XIMENA;
Revista chilena de historia natural , 2000, DOI: 10.4067/S0716-078X2000000100010
Abstract: the parasitic nematode pseudoterranova cattani sp. nov. is described from the stomach of the south american sea lion otaria byronia de blainville, sampled along the coastline off central-south chile, between 1980 and 1997. the adult and larvae of this species have been previously reported in the southeastern pacific ocean as phocanema decipiens myers. major differences with species from the north atlantic and northwest pacific are based on the body size, number, distance and size of caudal pillae
Las infracomunidades de parásitos de dos especies de Scartichthys (Pisces: Blenniidae) en localidades cercanas del norte de Chile
FLORES,KAREN; GEORGE-NASCIMENTO,MARIO;
Revista chilena de historia natural , 2009, DOI: 10.4067/S0716-078X2009000100004
Abstract: the infracommunities of metazoan parasites in two congeneric and sympatric marine fish species, scartichthys viridis (valenciennes 1836) and scartichthys gigas (steindachner 1876), were studied and compared between three localities of the intertidal rocky shore off the coast of northern chile, near iquique (20°32' s, 70°11' w), which were separated by no more than 6 km. samples were collected between august and september 2005. the goal of this study was to assess the variability in richness, abundance, diversity, dominance and parasite composition between close localities sampled within a short period. in all, 2,110 parasite individuals were collected from the 134 hosts examined, and 14 parasite taxa were identified. there was great similarity in the aggregated and compositional properties of the infracommunities, both between host species, as well as among study sites. we interpret these results as indicating that ecological factors such as habitat use and dietary composition, and evolutionary factors, such as the close relatedness between scartichthys species are the main causes influencing the high similarity found in parasite communities of these fish species.
Estabilidad temporal de las infracomunidades de parásitos en la borrachilla Scartichthys viridis (Valenciennes, 1836) (Pisces : Blenniidae) en la costa central de Chile
DíAZ,FREDDY; GEORGE-NASCIMENTO,MARIO;
Revista chilena de historia natural , 2002, DOI: 10.4067/S0716-078X2002000400001
Abstract: parasite infracommunities of the blenny scartichthys viridis (pisces: blenniidae) are compared among three samples taken within a 17-month period during three consecutive years (1999-2001), from intertidal pools at las cruces (33°27' s, 71°37' w), central chile. our goal is to assess if the richness, diversity, abundance and composition of parasite infracommunities are persistent or not through chronological time, as well as throughout the ontogeny of this herbivorous intertidal blenny. ten parasitic taxa were found in ca. 89 % of all 63 host blennies examined, eight of which were metazoans. protozoans were looked for in the last 2 years of the study only. seventy five percent of all eight metazoan taxa occurred in all three years, one was absent in one year, and another was present in one only. most of the blennies harbored protozoans. prevalence of protozoan cryptobia sp. was high in both years and lower in trichodina sp. in the overall sample, total host body length was a relevant predictor of the variations in composition, richness, total abundance and diversity of parasite infracommunities. in contrast, the year of sampling was not, especially when infracommunities compared came from hosts of similar body size. these results agree with those of parasite infracommunities found in other fish host species in chile, in that there is low compositional and aggregated variability along chronological time. the relative extension of ontogenetic versus chronological time is a subject to be explored further with respect to the amount of differentiation in these assemblages.
Conducta diurna del chungungo Lontra felina (Molina, 1782) en dos localidades de la costa de Talcahuano, Chile: ?efectos de la exposición al oleaje y de las actividades humanas?
Badilla,Manuel; George-Nascimento,Mario;
Revista de biología marina y oceanografía , 2009, DOI: 10.4067/S0718-19572009000200014
Abstract: the biology of the south american sea otter (lontra felina) is scarcely known along the chilean coast. in this study, habitat use during day time, and the behavior of this species are described, and compared between two localities: a protected embayment inhabited by artisanal fishermen and, an area of difficult access, both on the central-southern coast of chile. the study was carried out at the end of 2005 and beginning of 2006. despite the vicinity of the two studied localities (separated by ca. 9 km), there were differences in the time of peak diurnal activities, in duration of diving, and in the proportion of time devoted to socialization. at the most isolated and exposed locality sea otters were seen more frequently transiting in the water, and making long dives, while at the protected site, in vicinity of the fishermen village, diving was more frequent and shorter. habitat use was also different between localities according to the presence of human activities. some of these results contrast with other reports from chile and highlight the need to improve the knowledge of the factors affecting the behavior of lontra felina.
Asociación del parasitismo por Profilicollis bullocki (Paleacanthocephala, Polymorphidae) con la conducta y la pigmentación de Emerita analoga (Anomura, Hippidae) en Chile
Jerez,Rodolfo; George-Nascimento,Mario;
Revista de biología marina y oceanografía , 2010, DOI: 10.4067/S0718-19572010000300018
Abstract: the intermediate host of the acanthocephalan profilicollis bullocki in chile is the mole crab emerita analoga, a dominant species in sandy beaches, whereas the final hosts are marine birds. this parasite may affect the host phenotype because several studies about intermediate host-parasite systems where acanthocephalans participate, indicate modifications in host behavior. we experimentally assess if the parasite is able to modify the behavior and carapace pigmentation of naturally infected mole crabs. results suggest that p. bullocki induce changes in the e. analoga phenotype: hosts with more p. bullocki are less active and lighter in carapace pigmentation than those without or with less parasites. this might affect its ability to escape predators.
El parasitismo por Profilicollis bullocki (Acanthocephala: Polymorphidae) en Emerita analoga (Anomura: Hippidae) según condiciones contrastantes de abundancia de hospedadores definitivos en Chile
Zambrano,David; George-Nascimento,Mario;
Revista de biología marina y oceanografía , 2010, DOI: 10.4067/S0718-19572010000200009
Abstract: in chile, the intermediate host of the acanthocephalan profilicollis bullocki is the mole crab emerita analoga, with seabirds as the definitive hosts, who arrive in mass during summer, enhancing the spread of acanthocephalan eggs to the environment. thus, the magnitude of this parasitosis in e. analoga should attain higher values after the yearly arrival of seabirds. this study was performed in two periods contrasting in the abundance of marine birds, september-november 2008 (late winter-spring) and december 2008-january 2009 (summer), at 3 sandy beaches of the biobío region, chile. the abundance of birds was highest in summer, mainly due to the arrival of the franklin`s gull larus pipixcan to the study sites. it was observed that the cephalotorax length (lct) of e. analoga was much smaller in summer than in spring, and that the prevalence and abundance of p. bullocki increased with lct. although the prevalence of p. bullocki was higher before the arrival of birds, the slopes of the linear regressions between the abundance and intensity with lct were higher after the arrival of the birds to the study sites. these results are partly explained by the comparatively large lct of mole crabs before the arrival of seabirds, and by an intense recruitment pulse of small e. analoga after the arrival of seabirds, thus provoking a dilution effect on the prevalence.
Las infracomunidades de parásitos de dos especies de Scartichthys (Pisces: Blenniidae) en localidades cercanas del norte de Chile Parasite infracommunities of two blennid species, Scartichthys (Pisces: Blenniidae), at nearby localities off northern Chile
KAREN FLORES,MARIO GEORGE-NASCIMENTO
Revista chilena de historia natural , 2009,
Abstract: Se comparan las infracomunidades de parásitos de dos especies congenéricas y simpátridas de peces marinos: Scartichthys viridis (Valenciennes 1836) y Scartichthys gigas (Steindachner 1876) (Pisces: Blenniidae), en tres localidades del intermareal rocoso de Iquique (20°32' S, 70°11' O), norte de Chile, separadas por no más de 6 km, con muestras recolectadas entre agosto y septiembre de 2005. El objetivo fue evaluar la variabilidad de la riqueza, abundancia, diversidad, dominancia y composición en una escala espacial y temporal reducida. En total, se recolectaron 2.110 individuos parásitos en los 134 hospedadores examinados, los que pertenecían a 14 taxa. Se encontró una gran similitud en la composición y en las propiedades agregadas de las infracomunidades, tanto entre especies de hospedadores como entre sitios de estudio. Se interpreta que las condiciones ambientales, los factores ecológicos como el uso del habitat y de los recursos alimentarios, y los factores evolutivos como el alto grado de parentesco de estas especies de Scartichthys, son las principales influencias en la alta similitud parasitaria encontrada. The infracommunities of metazoan parasites in two congeneric and sympatric marine fish species, Scartichthys viridis (Valenciennes 1836) and Scartichthys gigas (Steindachner 1876), were studied and compared between three localities of the intertidal rocky shore off the coast of northern Chile, near Iquique (20°32' S, 70°11' W), which were separated by no more than 6 km. Samples were collected between August and September 2005. The goal of this study was to assess the variability in richness, abundance, diversity, dominance and parasite composition between close localities sampled within a short period. In all, 2,110 parasite individuals were collected from the 134 hosts examined, and 14 parasite taxa were identified. There was great similarity in the aggregated and compositional properties of the infracommunities, both between host species, as well as among study sites. We interpret these results as indicating that ecological factors such as habitat use and dietary composition, and evolutionary factors, such as the close relatedness between Scartichthys species are the main causes influencing the high similarity found in parasite communities of these fish species.
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