Showing papers by "National University of Comahue published in 1996"

A basal iguanodontian (Ornithischia: Ornithopoda) from the Late Cretaceous of South America

Abstract: The ornithopod dinosaur Gasparinisaura cincosaltensis gen. et sp. nov. is described. This new taxon from the Upper Cretaceous of northwest Patagonia (Argentina) represents the first report of basal iguanodontian ornithopods from South America. Gasparinisaura shares with the Dryomorpha the out-turned jugal-postorbital articulation, prominent lateral primary ridge in maxillary teeth, well-developed brevis shelf and metatarsal I reduced or absent. It retains a well-developed quadratojugal, low maxillary crowns, and a laterally compressed ischial shaft. The new taxon Euiguanodontia is erected to include Gasparinisaura cincosaltensis and the Dryomorpha (=Dryosauridae + Ankylopollexia).

Long-term evolution of multilocus traits.

Abstract: We analyze monomorphic equilibria of long-term evolution for one or two continuous traits, controlled by an arbitrary number of autosomal loci and subject to constant viability selection. It turns out that fitness maximization always obtains at long term equilibria, but in the case of two traits, linkage determines the precise nature of the fitness measure that is maximized. We then consider local convergence to long term equilibria, for two multilocus traits subject to either constant or frequency dependent selection. From a model of long-term dynamics near an equilibrium we derive a criterion of local long-term stability for 2-dimensional equilibria. It turns out that mutation can be a decisive factor for stability.

Pellegrinisaurus powellinov. gen. et sp. (sauropoda, titanosauridae) from the upper cretaceous of lago pellegrini, northwestern patagonia, argentina

Abstract: The holotype of Pellegrinisaurus powelli nov gen et sp, recovered from levels of AlIen Formation at lago Pellegrini (Province of Rio Negro, Argentina) is described Previous reference of this specimen to c Epachthosaurus sp is discarded, as it does not share derived features with the holotype of Epachthosaurus sciuttoi Powell Probable autapomorphies of Pellegrinisaurus powelli are: (1) transverse width of the centrum of the posterior dorsal vertebrae approximately twice the maximum dorsoventral depth, and (2) mid-posterior and posterior caudal vertebrae with anteroposteriorly elongated and dorsoventrally depressed neural spines, the anterior ends of which are higher anteriorly than posteriorly Pellegrinisaurus powelli is considered a probable sister taxon of the Saltasaurinae on account of low vertebral centra in the medial and posterior caudals, with dorso-ventrally convex lateral faces

Effects of pollinia removal and insertion on flower longevity inChloraea alpina (Orchidaceae)

Abstract: Although it is known that stigmatic pollen deposition may trigger early flower senescence, the existence of a similar plastic response of flower lifespan to pollen removal has been much less studied. Here we report on a factorial, manipulative experiment in which all 2 × 2 flower combinations of pollinia removal and stigmatic pollinia insertion were performed in inflorescences of the Patagonian ground orchidChloraea alpina. This experiment was conducted in the laboratory, in a population of cut inflorescences and in the field. We hypothesized that if expected fitness gains, through both the male and female functions, were weighed against the costs of flower maintenance, then early flower senescence should be triggered by either pollinia removal or insertion. The shortest flower lifespan would be expected in flowers where both processes occurred. Results showed that flower longevity was very strongly affected by pollinia insertion, reducing the flower lifespan by approximately 60%. The response of pollinia removal was much weaker. A significant reduction in flower longevity caused by pollinia removal was only detected in unpollinated flowers (i.e. no pollinia inserted). Within the racemose inflorescences, flowers in basal positions lived longer than flowers in terminal ones, which might be evidence of the importance of resource availability in determining maximum flower longevity. The observed responses of flower lifespan plasticity to pollinia manipulation only partially supported our expectations based on fitness benefit—cost relationships. Other factors that might explain these discrepancies are the different fitness gains that may indeed accrue to the processes of pollinia removal and insertion as they occur in nature, donor manipulation of the recipient flower lifespan associated with the evolution of pollen clustering into pollinia and physiological constraints in terms of the extent to which flower longevity may respond to pollen removal.

Diffusion by vacancy mechanism in Ni, Al, and Ni3Al: Calculation based on many‐body potentials

Abstract: The self-diffusion coefficients for the monovacancy mechanism, described in terms of the Arrhenius law, are calculated for Ni, Al, and the intermetallic compound Ni3Al by computer simulation techniques. Many-body interatomic potentials, based on the embedded atom model, are used together with the static relaxation method to study the static and dynamic properties of vacancies. The defect formation and migration energies, their corresponding relaxation volumes and vibration entropies, are evaluated. Special interest is devoted to the results obtained for Ni diffusion in Ni3Al. The present calculations predict that simple vacancy-Ni atom interchange jumps (both of ordered and disordered types) are energetically more favourable than the correlated six-jump cycles. Even though a difference in energies of δ = 0.35 eV favours migration via ordering jumps with respect to disordering jumps, the entropy factors behave in an opposite way suggesting that both types of jumps contribute to the Ni diffusion. Only for low temperatures (T ≤ 770 K) disordering jumps can be neglected. For this case, a pre-exponential factor D0 = 0.2 × m2 s−1 is obtained.

First evidence of an ankylosaur (dinosauria, ornithischia) in south america

Abstract: The holotype of Loncosaurus argentinus is removed from Theropoda and placed within Ornithopoda, due to the presence of a pendant fourth trochanter and trochanteric fossae. The taxon Loncosaurus argentinus is here considered a nomen vanum because of the absence of diagnostic characters. Among the Ornithopoda, no synapomorphies shared with the Ankylopollexia (higher iguanodontians + hadrosaurids) were observed.

Relationship between seed and spore banks and vegetation of a mountain flood meadow (mallín) in Patagonia, Argentina

Abstract: Soil seed and spore banks are seen to affect the composition and structure of plant communities, especially in wetlands This study was conducted in a flooded mountain meadow (mallin) in the Nahuel Huapi National Park, Patagonia, Argentina Species density and composition were determined for spring (November 1989) and autumn (April 1990) using the emergence technique Viable diaspore (ie, seed and spores) density was greater for autumn samples (17,063 m−2) than for spring samples (10,047 m−2) A sizeable pool of fern spores was also found, which represented 178 and 602% of the autumn and spring collections, respectively Species composition of the seed and spore banks varied seasonally, and seeds of the dominant mallin species were only present in autumn Seed bank species were mostly perennials, exceptMimulus parviflorus The composition of the seed bank compared with that of the above-ground vegetation yielded a relatively low correlation between germinable seeds in the soil and the surface plant community In addition, no ferns were present in the surface community These results suggest that neither seed nor spore banks control mallin vegetation dynamics, probably because perennial and rhizomatous plants are the dominant components of the wetland community

Zwischenartliche Beziehungen zwischen freilebenden Guanaco (Lama guanicoe) und angesiedeltem Rotwild (Cervus elaphus) in Argentinien

Abstract: Das in Argentinien eingefuhrte Rotwild besiedelt derzeit grose Gebiete von Patagonien. Das Verbreitungsgebiet uberschneidet sich teilweise mit der Verbreitung der einheimischen Kamelart Guanaco. Die vorliegende Mitteilung beschreibt direkte Beziehungen zwischen den beiden Arten in einem Okotongebiet des Nahuel Huapi Nationalparks. Beide Arten wurden oft zusammen beim Asen an gleichen Orten und zur gleichen Zeit beobachtet, und die Distanz zwischen Individuen beider Arten war z. T. weniger als ein Meter. Dadurch entsteht die Moglichkeit, das es zur Futterkonkurrenz kommt, vor allem da die floristische Artenvielfalt sehr gering ist. Zudem konnte diese Vertraglichkeit des Verhaltens die Epidemiologie verschiedener Krankheiten beider Arten beeinflussen. Obwohl Gruppen von Guanacos ihr Territorium gegen andere Gruppen verteidigen, akazeptieren sie Gruppen von Rotwild, ohne Aggressivitat zu zeigen.

Growth factors controlling periphyton production in a temperate reservoir in Patagonia used for fish farming

Abstract: In the early stages of pollution it is not always possible to detect contamination by chemical parameters as some components of the biota react more rapidly to inputs of pollutants. The purpose of this work is to determine the importance of nutrient inputs as a control of growth of the periphyton community and to evaluate the feasibility of using changes in the periphyton community to monitor the effects of contamination from fish farms. Wastes derived from fish farming in the Alicura Reservoir changed the nutrient concentrations of the sediment just below the fish cages and decreased the nitrogen: phosphorus (N:P) ratio to below 1. This situation stimulated the development of cyanophytes and increased the total algal biomass as a consequence of higher nutrient availability. In laboratory bioassays, diatoms dominated the periphyton community at high N:P (>4) and Si:P (> 1000) ratios, while cyanophytes were dominants at low N:P and Si:P (< 10) ratios. These results suggested that not only the N:P ratio controls periphyton composition, because in the reservoir (where N:P ratio was always low) the periphyton was dominated by diatoms as a result of the presence of extremely high Si:P ratios (3000-5000). These results suggest that periphyton is a powerful tool for detecting the first signs of contamination.

AC conductivity in dispersed ionic conductors: the effective medium approximation

Abstract: We developed a stochastic transport theory for the calculation of the ac-conductivity in two-phase mixture materials (with high interface conductance). A perturbation around the different configurational interface paths is introduced by using the Effective Medium Approximation (EMA). Data of LiI conductivity after the addition of an insulating second phase Al2O3 show that our approach describes the main features of the ac-conductivity. The dielectric constant and the static effective capacitance, as a function of the concentration of the insulating material, are compared against previous Monte Carlo simulations and Renormalization Group results. Conductivity (Cole-Cole plots) and dielectric properties of dispersed ionic conductors are studied in a self-consistency way. A random walk in a random-resistor network and the use of an effective electric circuit are presented in order to describe all the features of the ac-response in these materials.

Kann Energiemangel ein Massensterben unter Cerviden in Sommereinständen der nördlichen Gebirge verursachen? Eine exploratorische Analyse am Schwarzwedelhirsch (Odocoileus hemionus columbianus)

Abstract: Nahrungsbedingte Probleme bei Cerviden, die auf Energiemangel in Sommer/Herbsteinstanden in nordlichen und gemasigten Berggebieten zuruckzufuhren sind, wurden bisher nicht beschrieben. Das kommt z. T. von der traditionellen Interpretierung, das die Verfassung des Wintereinstandes oder die klimatischen Bedingungen im Winter fur Energiemangel und die daraus folgenden Massensterben verantwortlich sind. Hingegen kann sowohl die Verfassung des Wintereinstandes wie des Sommerein-standes einen Hirschbestand einschranken, wenn diese an die Tragfahigkeit einer vom Menschen veranderten Umwelt herangelangt ist. Die vorliegende Arbeit analysiert Umstande, die fur einen progressiven Zerfall der Verfassung eines Wildbestandes mit schlusendlichem Massensterben sprechen. Zwischen Mai und September von 1987 verendete ein groser Teil des weiblichen Bestandes von Cow-Creek-Schwarzwedelwild(Odocoileus hemionus columbianus). Die Sterblichkeitsrate der radiomarkierten Alttiere sprang im Sommer auf 41% im Vergleich zu 9% in den vorherigen 3 Sommern (n = 67). Mehrere Alttiere wurden in ruhender Stellung ohne Anzeichen von Raubtieren oder Krankheiten gefunden. Das Durchschnittsalter nahm von 8,3 Jahren (±4,9 SD, Bereich von 1,5–18,5 Jahren) wahrend der Jahre von 1984–87 auf 4,5 Jahre (± 2,5, Bereich von 1,5–10,5 Jahren) im Jahre 1988 ab. Auch Anderungen im Verhaltnis von Hirschen zu Alttieren deuteten auf eine Reduzierung von 27–45% des weiblichen Bestandes im Sommer hin. Zudem sprach das Kalb/Alttier-Verhaltnis im folgenden Winter fur eine weitere Reduzierung des Bestandes wahrend des Winters 1987/88. Fettreserven im Herbst nahmen uber die 4 Jahre progressiv ab und erreichten 1987 ein Tief, wie es normalerweise nur bei im Winter verhungerten Cerviden angetroffen wird. Das Kalb/Alttier-Verhaltnis im Herbst 1988 war das hochste je registrierte in diesem Bestand. Historische Berichte uber das Gebiet und die Wilddichte stehen in starkem Kontrast zu der aktuellen Situation, welche auf die Art der Landnutzung zuruckzufuhren ist. Wir vermuten, das Anderungen in der Dynamik von Nahrstoffen und Erhaltlichkeit von Nahrungspflanzen fur die gegenwartige Einschrankung des Bestandes durch Nahrungsenergie verantwortlich sind.

Mechanical aquatic weed management in the lower valley of the Río Negro, Argentina

Abstract: A major irrigation system in the Lower Valley of the Rio Negro, Argentina, has been invaded by aquatic plants, with Potamogeton illinoensis Morong dominant in irrigation channels and Potamogeton pectinatus L. dominant in drainage channels. Although several other macrophytes are present, problems are largely caused by the dominant species. Results are presented for plant biomass response to weed control treatments using a chain-cutting method in the principal irrigation channel of the system. Peak above-ground biomass of Potamogeton illinoensis was reduced by about 38% by this physical control regime. The treated populations regrew rapidly after spring clearance, but did not regrow after subsequent mid- and late-season clearance operations, even though untreated population biomass remained high during this period. The highest density of Potamogeton illinoensis ramets was found in treated areas. Chain- cutting produced no discernible effect on dissolved oxygen, water temperature, water conductivity, pH or light extinction coefficient compared with untreated check sectors of the channel.

Studies on vegetative production of Potamogeton illinoensis Morong in southern Argentina.

Abstract: Potamogeton illinoensis Morong is a major submerged weed invading irrigation channels in the Lower Valley of the Rio Negro, near Viedma, Argentina. Studies on morphology and growth characteristics of this species were conducted in an outdoor tank from August 1993 to May 1994 with the objective of increasing the knowledge of its ecology order to adjust control measures. The maximum aboveground biomass was reached in April, with a subsequent decrease to May when the water supply was cut off. Belowground biomass comprised two kinds of rhizomes. The first group (Rhizomes I) was produced from the beginning of the annual cycle causing both lateral shoots and new rhizomes I production. The second group (Rhizomes II) was distinguished as an enlargement of the extremes of rhizomes I from mid-November, producing only short overwintering sprouts. Plant parts production (DW in g/plant) in the first cycle was: 27.2 g leaves; 11.9 g stems; 17.4 g rhizomes I and 8.1 g rhizomes II. Vegetative propagation appeared to be an important survival strategy in this species. During the 3-4 month period without water only rhizomes with underground overwintering sprouts survive in the dry sediment.

Growth of Odontesthes bonariiensis (Atherinidae) larvae feeding on suboptimal zooplankton densities

Abstract: In this study we investigate the effect of food availability (zooplankton biomass) on the growth of Odontesthes bonariensis (Atherinidae) larvae. The larvae were stocked in four 45 m2 outdoor tanks at relatively high densities (100 and 200 larvae m−2). Because of the high stocking densities, the zooplankton biomass was depleted in all tanks. However, the patterns of food limitation, and particularly periods of severe food shortage, differed in tanks stocked at different densities. We could therefore, observe the effect of food limitation in larvae that differed in weight and age. The effects of variables suspected to influence O. bonariensis growth rates (age and weight of larvae, available zooplankton biomass, mean individual weight of available preys, total ingested prey weight, and mean weight of ingested preys) were investigated using standard multiple regression methods, and a model assuming: (1) an allometric relationship between maximum growth rates and weight of larvae, and (2) an inverse relationship between growth depression and the available zooplankton biomass. Both methods were consistent in showing that only the weight of larvae, and the availability of zooplankton prey had significant effects on the growth of O. bonariensis. The model's results additionally suggest that, if the observed growth rates are scaled by the maximum growth rate corresponding to the larva weight, the effect of zooplankton biomass is largely independent of age and weight of larvae.

Optimal parallel model solutions using the polynomial approach

Abstract: Solutions to the optimal filtering and open-loop control problems using a generalized parallel model scheme are presented. The solutions are based on the algebra of polynomial matrices. Different c...

Las megaturbiditas de la Formacion Empozada: un modelo interpretativo para el Ordovicico turbiditico de la precordillera argentina

Abstract: RESUMEN. El Miembro Inferior de la Formacion Empozada (Ordovicico medio y Superior), expuesto en el extremo sur de la precordillera argentina, Provincia de Mendoza, consiste en 305 m de brechas, pelitas verdes, areniscas, paraconglomerados y pelitas negras, que rematan la sucesion. Esta secuencia conforma dos episodios de depositos de talud, en cambio las pelitas negras se interpretan asociadas a una cuenca profunda. El contenido paleontologico autoctono esta compuesto, casi exclusivamente, por graptofauna que permite definir las Zonas de Paraglossograptus tentaculatus, Nemagraptus gracilisy Climacograptus bicornis, ubicando cronoestratigraficamente la sucesion en el Llanvirniano, Llandeillano tardio-Caradociano basal y Caradociano; por otro lado, se han identificado restos fosiles en el material resedimentado, olistolitos, algunos de gran tamano, los cuales indican diversas edades del Cambrico y Ordovicico Inferior. En este trabajo, se describen y caracterizan estos cuerpos provenientes de areas de plataforma y talud carbonatico y clastico. Se correlaciona esta unidad con otras similares en el contexto regional, lo que permite individualizar dos eventos deposicionales diferentes, asociados a una actividad tectonica importante. ABSTRACT. Megaturbidites of Empozada Formation: an interpretative model of the turbiditic Ordovician of the Argentinian precordillera. The Lower Member of the Empozada Formation (middle and Upper Ordovician) is discontinuously exposed in the southern end of the Argentinian precordillera, in Mendoza Province. It is composed by 305 m of megabreccias and breccias, green shales, mudstones and sandstones, paraconglomerates and black shales that culminate the succession. These outcrops conform slope deposits. They are associated to two different Systems Tracts. The black shales are interpreted as a Transgressive Event. The autochtonous paleontological material is mostly composed of graptolites, which enable to define the Paraglossograptus tentaculatus Zone (Llanvirnian), Nemagraptus gracilis Zone (Upper Llandeillo-Early Caradocian) and the Climacograptus bicornis Zone (Caradocian). On the other hand, fossil material was identified on Cambrian and Ordovician allochtonous rocks. These Olistoliths, derived from carbonate platforms and talus, are recorded in this paper. This succession is compared with similar rocks on the regional context. This allows to verify two sea-Ievel events associated to an important tectonic activity.

Keratella distribution in North Patagonian lakes (Argentina)

Abstract: The distribution of Keratella species from 15 different lakes in North Patagonia (Argentina) was analysed. The genus was not present at altitudes above 1000 m. K. tropica was restricted to Patagonian Plateau lakes with a comparatively high conductivity. A morphometric analysis of the widely distributed K. cochlearis was performed. Results showed three groups of K. cochlearis corresponding to Andean lakes, Patagonian Plateau lakes and a Patagonian Reservoir.

Patrones morfológicos y florísticos en los bosques andino-patagónicos de Argentina

Abstract: The morphological patterns of forests of Nahuel Huapi National Park 41°S (Northern Patagonia) were analyzed and compared with those ofthe forests at 51oS (Southern Patagonia), Argentina. The deciduous and evergreen forests of Northern Patagonia were heterogeneus in floristic composition but similar in plant morphology. Their component species were mainly intolerant to low rainfall, and their growth forms suggested that competition for light is an important structuring force. At 51 ° South latitude, the species of the deciduous and evergreen forests were morphologically diverse, since the deciduous forests of this latitude are characterized by morphologies typical of more xeric and open environments, and the species are tolerant to low rainfall. The morphological patterns of the deciduous forests at both latitudes show the floristics differences in species and families due to different positions in the regional climatic and disturbance gradient.

Fluctuación estacional de grupos tróficos de nemátodos en un bosque central de Austrocedrus chilensis en Argentina

Abstract: The seasonal fluctuation of nematode trophic groups associated with Austrocedrus chilensis forest in the east border of its distribution in the Andean-Pa tagon ian forest (Argentina) was studied. Both soil depth and t ime of the year were considered as var iables . The abundance of nematodes did not vary significantly through the year. The time of the year can be influencing in different ways both each trophic group and the species they compromise . Each t rophic group responds to soil depth in a part icular way. The highest popula t ion levels were found in plant­ parasitic, followed by omnivorous and microbivorous with very similar density, fungivorous, and very scarse predatious nematodes .