Cambios en la ecología trófica de los depredadores apicales del Mar Argentino durante el Holoceno

[spa] El Mar Argentino ha sufrido un impacto humano creciente desde el Holoceno medio hasta hoy en día, fruto del cual se han producido importantes cambios en los niveles más altos de la red trófica. Las actividades extractivas (caza y pesca), tanto la aborigen como la actual, tienen la tendencia a explotar las especies de mayor tamaño, produciendo el efecto conocido en gestión de pesquerías como “fishing down the food web”. En otras palabras el impacto humano llevaría a cadenas tróficas más cortas como consecuencia de la extinción de los depredadores apicales. Sin embargo, las especies que sobreviven a la explotación, si bien reducidas drásticamente en número de individuos, permanecen en el ecosistema y desempeñan un papel trófico. En esta tesis se han analizado los cambios que ocurrieron en la red trófica del Mar Argentino durante el Holoceno medio y tardío como consecuencia de la actividad humana, centrándose principalmente en dos de sus depredadores más abundantes: el lobo marino común (Otaria flavescens) y el lobo marino fino (Arctocephalus australis). Por un lado se observó que los cazadores-recolectores no tuvieron un impacto relevante sobre los patrones de uso del hábitat y alimentación de estas dos especies, ya que durante todo el Holoceno no se produjeron apenas cambios en sus dietas. Sin embargo, sí variaron los patrones de explotación de pinnípedos por parte de los aborígenes, seguramente como consecuencia de cambios en la producción primaria marina que debido a una posible sobreexplotación de los pinnípedos. No hay duda, por el contrario, de que los cambios radicales en la dieta de ambas especies de lobos marinos observados hace unos 150 años fueron la consecuencia de su extinción virtual en el Mar Argentino entre los siglos XVIII y XX. A la vez que las dietas cambiaron, la red trófica se alargó y se hizo menos redundante. Estos sorprendentes resultados se pueden interpretar como la respuesta de los depredadores apicales a la disminución de la presión intraespecífica generada por la explotación humana. Los estudios históricos como la presente tesis pueden ayudar a comprender los mecanismos que actúan en ecosistemas perturbados por la actividad humana y ofrecer una perspectiva más amplia para su restauración.[eng] The Argentine Sea has suffered increasing human impact from the middle Holocene until today, and significant changes in high levels of the marine food web are the result of such an impact. Both aboriginal and industrial exploitation of marine resources (hunting and fishing) are characterised by the preferential removal of the largest species, a process that is supposed to shorten size-structured marine food webs. This process is known in fisheries management as "fishing down the food web" because the human impact would shorten the food chains as a result of the extinction of the top predators. However, the species that are not extinguished remain in the ecosystem and play a trophic role, although they are drastically reduced in number. This thesis analyzed the changes that occurred in the food web of the Argentine Sea during the middle and late Holocene as a result of human activity, mainly focusing on two of its most abundant predators: the South American sea lion (Otaria flavescens) and the South American fur seal (Arctocephalus australis). It was observed that hunter-gatherers did not have a significant impact on habitat use patterns and trophic ecology of these two species, since there were no changes in their diets throughout the Holocene. However, the patterns of exploitation of pinnipeds by aborigines varied through time, probably as a result of changes in marine primary productivity more than overexploitation of pinnipeds by hunter-gatherers. There is no doubt, however, that the radical changes observed about 150 years ago in the diet of both sea lion and fur seal were the result of their virtual extinction in the Argentine Sea between the 18th and 20th century, during the fur trade. While diets changed the food web became longer and less redundant. These surprising results can be interpreted as the response of top predators to the decrease of the intraspecific pressure generated by the human impact. Historical studies such as this thesis may help to understand the mechanisms playing in ecosystems disturbed by human activity and provide a broader perspective for their restoration

Effect of alloying elements in melt spun Mg-alloys for hydrogen storage

In this paper we report the effect of alloying elements on hydrogen storage properties of melt-spun Mg-based alloys. The base alloys Mg90Si10, Mg90Cu10, Mg65Cu35 (at%) were studied. We also investigated the effect of rare earths (using MM: mischmetal) and Al in Mg65Cu25Al10, Mg65Cu25MM10 and Mg65Cu10Al15MM10 alloys. All the melt-spun alloys without MM show a crystalline structure, and the Mg65Cu25MM10 and Mg65Cu10Al15MM10 alloys showed an amorphous and partially amorphous structure respectively. At 350˚C all the alloys had a crystalline structure during the hydrogen absorption-desorption tests. It was observed that Si and Cu in the binaries alloys hindered completely the activation of thehydrogen absorption. The partial substitution of Cu by MM or Al allowed activation. The combined substitution of Cu by MM and Al showed the best results with the fastest absorption and desorption kinetics, which suggests that this combination can be used for new Mg-alloys to improve hydrogen storage properties.Fil: Rozenberg, Silvia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería ; ArgentinaFil: Saporiti, María Fabiana Sonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería ; ArgentinaFil: Lang, Julien. Université du Québec a Montreal; CanadáFil: Audebert, Fernando Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; ArgentinaFil: Botta, Pablo Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Stoica, Mihai. Leibniz Institute for Solid State and Materials Research Dresden; AlemaniaFil: Huot, Jacques. Université du Québec a Montreal; CanadáFil: Eckert, Jürgen. The Erich Schmid Institute of Materials Science; Austri

Longer and less overlapping food webs in anthropogenically disturbed marine ecosystems: confirmations from the past

The human exploitation of marine resources is characterised by the preferential removal of the largest species. Although this is expected to modify the structure of food webs, we have a relatively poor understanding of the potential consequences of such alteration. Here, we take advantage of a collection of ancient consumer tissues, using stable isotope analysis and SIBER to assess changes in the structure of coastal marine food webs in the South-western Atlantic through the second half of the Holocene as a result of the sequential exploitation of marine resources by hunter-gatherers, western sealers and modern fishermen. Samples were collected from shell middens and museums. Shells of both modern and archaeological intertidal herbivorous molluscs were used to reconstruct changes in the stable isotopic baseline, while modern and archaeological bones of the South American sea lion Otaria flavescens, South American fur seal Arctocephalus australis and Magellanic penguin Spheniscus magellanicus were used to analyse changes in the structure of the community of top predators. We found that ancient food webs were shorter, more redundant and more overlapping than current ones, both in northern-central Patagonia and southern Patagonia. These surprising results may be best explained by the huge impact of western sealing on pinnipeds during the fur trade period, rather than the impact of fishing on fish populations. As a consequence, the populations of pinnipeds at the end of the sealing period were likely well below the ecosystem's carrying capacity, which resulted in a release of intraspecific competition and a shift towards larger and higher trophic level prey. This in turn led to longer and less overlapping food webs

Short range order in Al-Fe-Nb, Al-Fe-Ce and Al-Ni-Ce metallic glasses

Short range order of amorphous samples with Al90Fe7Nb3, Al90Fe5Ce5 and Al90Ni5Ce5 nominal composition (in at.%) was studied by X-ray diffraction (XRD) at room temperature (RT). The total structure factors STot(Q) and the reduced atomic distribution function G(r) were derived from the diffracted intensity IM(Q). All the STot(Q) factors are composed by an initial prepeak followed by a main peak and a second peak with two components. Though the general aspect of the different samples is similar they present slight differences in details that are discussed as a function of the composition and compared with available data in the literature. While in the Al-(Fe, Ni)-Ce alloys two distinct components were observed for the first peak of the G(r) function, a unique broad peak was observed in the Nb containing alloy. The pair correlation function, g(r), for Al90Fe10 at 200 K have been calculated with molecular dynamics simulation (MDS) and it is in good agreement with the experimental results obtained from Al90Fe7Nb3 showing that size effects can be neglected in this sample.Fil: Saporiti, María Fabiana Sonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; Argentina. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Mecánica. Grupo de Materiales Avanzados; ArgentinaFil: Boudard, Miguel Santiago. Centre National de la Recherche Scientifique; Francia. Institut Politechnique de Grenoble; Francia. Universite Joseph Fourier; FranciaFil: Audebert, Fernando Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; Argentina. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Mecánica. Grupo de Materiales Avanzados; Argentin

The use of Nb in rapid solidified Al alloys and composites

The worldwide requirements for reducing the energy consumption and pollution have increased the demand of new and high performance lightweight materials. The development of nanostructured Al-based alloys and composites is a key direction towards solving this demand. High energy prices and decreased availability of some alloying elements open up the opportunity to use non-conventional elements in Al alloys and composites. In this work the application of Nb in rapid solidified Al-based alloys and Al alloys matrix composites is reviewed. New results that clarify the effect of Nb on rapid solidified Al alloys and composites are also presented. It is observed that Nb stabilises the icosahedral Al–Fe/Cr clusters, enhances the glass forming ability and shifts the icosahedral phase decomposition towards higher temperatures. Nb provides higher corrosion resistance with respect to the pure Al and Al–Fe–RE (RE: rare earth) alloys in the amorphous and crystalline states. The use of Nb as a reinforcement to produce new Al alloy matrix composites is explored. It is observed that Nb provides higher strength, ductility and toughness to the nanoquasicrystalline matrix composite. Nb appears as a new key element that can improve several properties in rapid solidified Al alloys and composites.Fil: Audebert, Fernando Enrique. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Mecánica. Grupo de Materiales Avanzados; Argentina. University of Oxford; Reino Unido. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; ArgentinaFil: Galano, Marina Lorena. University of Oxford; Reino Unido. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Saporiti, María Fabiana Sonia. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Mecánica. Grupo de Materiales Avanzados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Fishing alters the ecological significance of colour morphs in a temperate coastal fish

Resource partitioning in polymorphic fish species is expected to be altered by human exploitation, as individual specialization is density dependent in many vertebrates. We tested this hypothesis using the ballan wrasse Labrus bergylta as a model species. We compared the isotope niches of the plain and spotted morphs of the species in a marine protected area (MPA) and in adjoining areas open to fishing, both off Galicia (NW Spain). Underwater visual census confirmed a threefold increase in the biomass of the ballan wrasse off Cíes Islands compared to areas open to recreational fishing, thus demonstrating that populations outside MPAs are well below carrying capacity. The stable isotope ratio of C revealed differences in the resource use patterns of plain and spotted ballan wrasses both in areas open and closed to fishing, as plain wrasses were always depleted in 13C compared to sympatric spotted ones. The stable isotope ratio of N showed that plain ballan wrasses foraged consistently at a higher trophic level than spotted ones in areas of high population density closed to recreational fishing, whereas differences did not exist or were reversed in areas open to fishing. These results demonstrate that the pattern of trophic resource partitioning two morphs of the ballan wrasse is density-dependent and that plain and spotted ballan wrasses likely had different ecological niches in pristine ecosystems

Feeding ecology of dusky dolphins Lagenorhynchus obscurus: evidence from stable isotopes

The dusky dolphin Lagenorhynchus obscurus occurs in the Southern Hemisphere, where it is restricted to coastal temperate areas. This study aimed to characterize the feeding ecology of dusky dolphins inhabiting northern and central Patagonia by using δ13C and δ15N stable isotope ratios in skin samples. We searched for evidence of geographical and seasonal variation in diet and we explored dietary differences between sexes. Significant differences in the stable isotope ratios of dusky dolphins were found among the 4 gulfs under udy. Skin samples from Golfo San Matías and Golfo San Jorge were 13C-enriched and 15N-depleted ompared to those from Golfo Nuevo and Golfo San José. There was no seasonality in the diet at Golfo Nuevo, and no differences in the diet between sexes in any gulf. Furthermore, Bayesian ellipses of males and females were similar in size and the overlap was mostly symmetrical in Golfo San José and Golfo San Jorge, while in the Golfo San Matías and Golfo Nuevo, females had wider ranges of δ15N, suggesting the xploitation of a wider trophic niche. Finally, pelagic fishes and demersal pelagic squids were identified as the main prey for this species of dolphin, although the proportion of each prey varied regionally.El delfín oscuro Lagenorhynchus obscurus se distribuye ampliamente en el Hemisferio Sur, donde prefiere áreas templadas costeras. Este estudio tuvo como objetivo caracterizar la ecología trófica de delfines oscuros que habitan en el norte y centro de la Patagonia mediante el uso de isótopos estables de δ 13 C y δ 15 N en muestras de piel. Específicamente, buscamos evidencia de variación geográfica y estacional en la dieta de los delfines y exploramos la diferencia de dieta entre sexos. Se encontraron diferencias significativas en los valores de isótopos estables de los delfines entre los cuatro golfos bajo estudio. Las muestras de piel de Golfo San Matías y Golfo San Jorge se encuentran enriquecidas en 13 C y deprimidas en 15 N en comparación con las muestras del Golfo Nuevo y Golfo San José. No hubo estacionalidad en la dieta en el Golfo Nuevo, y no hay diferencias en la dieta entre sexos en ningún golfo. Además, las elipses bayesianas de machos y hembras fueron similares en tamaño y la superposición fue mayormente simétrica en el Golfo San José y el Golfo San Jorge, mientras que en el Golfo San Matías y el Golfo Nuevo, las hembras tienen rangos más amplios de δ 15 N, lo que sugiere la explotación de un nicho trófico más amplio. Por último, los peces pelágicos y los calamares demersales pelágicos fueron identificados como la presa principal de esta especie de delfín, aunque la contribución de cada presa varió regionalmente.Fil: Loizaga de Castro, Rocio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Saporiti, Fabiana. Universidad de Barcelona. Facultad de Biología. Departamento de Biología Animal; EspañaFil: Vales, Damián Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Garcia, Nestor Anibal. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Cardona, Luis. Universidad de Barcelona. Facultad de Biología. Departamento de Biología Animal; EspañaFil: Crespo, Enrique Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentin