Northwestern Argentina (NWA) is a region characterized by a complex geomorphology, and encompasses six ecoregions in a relatively small area. The environmental heterogeneity of NWA and the ...sensitivity of small mammals towards environmental and landscape changes constitute a good scenario to assess the factors that influence small mammal diversity patterns in the region. We studied small mammal communities obtained from pellet samples in 24 localities of NWA. We identified 50 non-volant small mammal species and obtained topographic, climate and land cover variables. Our results show that small mammal communities respond to environmental factors at a regional scale. Such variations were explained in different proportions by the geographic position of the collecting sites, landscape and climate. Furthermore, the combined effect of these factors was the main determinant of species abundance patterns. Our results support the need of large-scale approaches to study communities, since the explanations of the observed patterns are simpler and more general. We emphasize the importance of considering the combined effect of different environmental predictors, which allows determining the amount of species variation that is spatially structured, and within that, the amount of variation related to the influence of the measured environmental variables.
Abstract We study the geographical variation of the skull in the cavies Microcavia australis and M. maenas and its association with environmental variables. We tested four hypotheses previously ...proposed to explain the geographic patterns of morphological variation i) heat conservation; ii) heat dissipation; iii) primary productivity and iv) seasonality. We used 16 cranial measurements taken from 180 individuals. We analyzed the spatial variation in cranial morphology through Generalized Additive Models. Both species showed a north-south clinal gradient in skull size (increasing towards colder, less seasonal environments, with lower summer rainfalls in M. australis and towards warmer and seasonal environments in M. maenas). Microcavia australis presented greater ecomorphological variability than M. maenas, in agreement with its wider distribution and occurrence in more diverse environments. Also, the length of tympanic bullae in M. australis was larger towards its northern distributional range (associated to smaller skulls), and smaller to the south (associated to larger skulls). Overall, the distributional range of both species coincided with unproductive environments, where temperature represents a limiting factor and, together with rainfall, might determine the observed morphological patterns.
Resumen “Pioneras: Las Científicas del Museo Argentino de Ciencias Naturales” es un ciclo que se inició en el mes de marzo del año 2019 en el marco del Día Internacional de la Mujer. Este ciclo ...surgió a partir de un grupo de mujeres autoconvocadas del Museo y tiene por objetivo reconocer y homenajear la labor de las primeras mujeres que desempeñaron actividades científicas dentro de nuestra Institución. En su tercera edición (2021), el ciclo rindió homenaje a tres brillantes profesionales y pioneras de la aracnología: Berta S. Gerschman de Pikelin, Rita D. E. Schiapelli y María Elena Galiano. Estas tres investigadoras han dedicado su carrera científica al estudio de arañas neotropicales. A lo largo de su trayectoria, no sólo han dado origen a la Colección Nacional de Aracnología del Museo, sino que también han dejado un legado de más de 150 trabajos científicos publicados y alrededor de 200 nuevas especies descriptas, construyendo una base sólida para investigaciones futuras.
Existen pocos antecedentes sobre los hábitos tróficos de Tyto furcata en el noroeste argentino, y ninguno en la ecorregión de las Yungas. A partir del análisis de egagrópilas, caracterizamos la dieta ...de esta rapaz en seis localidades de las Yungas de Argentina. Documentamos la composición y la diversidad de los ítems presa y analizamos los parámetros tróficos en el contexto de los diferentes grados de transformación de la vegetación. El estudio incluyó una caracterización general y un análisis estacional. Los roedores constituyeron un 98% del total de presas y fueron los que más aportaron a la dieta en términos de biomasa. Los valores de amplitud de nicho trófico (ANT) y del nicho trófico estandarizado fueron más elevados en comparación con los observados en otras áreas de Argentina. Observamos cambios estacionales importantes en la composición de especies para cada localidad. La ANT fue mayor durante la estación húmeda y el solapamiento trófico entre estaciones fue relativamente alto. No observamos una relación clara entre el grado de modificación antrópica y los parámetros tróficos. Nuestros resultados coinciden con los reportados para América del Sur, con un espectro relativamente amplio de presas y una fuerte selección por roedores cricétidos. Algunas localidades mostraron una tendencia a la disminución de ANT durante la estación seca, lo que reflejaría las variaciones estacionales en la abundancia de pequeños mamíferos, que muestran mayores tamaños poblacionales en invierno. Esto obligaría a la lechuza a adoptar una dieta más generalista en el verano. En estas localidades, la proporción de los diferentes usos del suelo no parece tener una incidencia importante sobre los parámetros tróficos analizados, al menos en nuestra escala de análisis. Aunque nuestros resultados constituyen un punto de partida importante para el estudio del nicho trófico de Tyto furcata en Yungas, resulta evidente la necesidad de estudios adicionales para dilucidar numerosos aspectos vinculados a la ecología de esta rapaz.
We present observations of a major outburst at centimeter, millimeter, optical, X-ray, and gamma -ray wavelengths of the BL Lacertae object AO 0235+164. We analyze the timing of multi-waveband ...variations in the flux and linear polarization, as well as changes in Very Long Baseline Array images at lambda = 7 mm with similar to 0.15 milliarcsec resolution. The association of the events at different wavebands is confirmed at high statistical significance by probability arguments and Monte Carlo simulations. A series of sharp peaks in optical linear polarization, as well as a pronounced maximum in the 7 mm polarization of a superluminal jet knot, indicate rapid fluctuations in the degree of ordering of the magnetic field. These results lead us to conclude that the outburst occurred in the jet both in the quasi-stationary 'core' and in the superluminal knot, both parsecs downstream of the supermassive black hole. We interpret the outburst as a consequence of the propagation of a disturbance, elongated along the line of sight by light-travel time delays, that passes through a standing recollimation shock in the core and propagates down the jet to create the superluminal knot. The multi-wavelength light curves vary together on long timescales (months/years), but the correspondence is poorer on shorter timescales. This, as well as the variability of the polarization and the dual location of the outburst, agrees with the expectations of a multi-zone emission model in which turbulence plays a major role in modulating the synchrotron and inverse Compton fluxes.
We present observations of a major outburst at centimeter, millimeter, optical, X-ray, and gamma-ray wavelengths of the BL Lacertae object AO 0235+164. We analyze the timing of multi-waveband ...variations in the flux and linear polarization, as well as changes in Very Long Baseline Array (VLBA) images at 7mm with 0.15 milliarcsecond resolution. The association of the events at different wavebands is confirmed at high statistical significance by probability arguments and Monte-Carlo simulations. A series of sharp peaks in optical linear polarization, as well as a pronounced maximum in the 7 mm polarization of a superluminal jet knot, indicate rapid fluctuations in the degree of ordering of the magnetic field. These results lead us to conclude that the outburst occurred in the jet both in the quasi-stationary "core" and in the superluminal knot, both parsecs downstream of the supermassive black hole. We interpret the outburst as a consequence of the propagation of a disturbance, elongated along the line of sight by light-travel time delays, that passes through a standing recollimation shock in the core and propagates down the jet to create the superluminal knot. The multi-wavelength light curves vary together on long time-scales (months/years), but the correspondence is poorer on shorter time-scales. This, as well as the variability of the polarization and the dual location of the outburst, agrees with the expectations of a multi-zone emission model in which turbulence plays a major role in modulating the synchrotron and inverse Compton fluxes.
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