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Omar Torrescarvajal - One of the best experts on this subject based on the ideXlab platform.
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sistematica filogenetica de las lagartijas del genero stenocercus squamata iguania de los Andes del norte
Revista Mexicana de Biodiversidad; Vol 80 No 003, 2011Co-Authors: Omar TorrescarvajalAbstract:El genero Stenocercus esta compuesto por 61 especies que se distribuyen principalmente en los Andes y tierras bajas aledanas (0-4 000 m), desde el norte de Colombia y Venezuela hasta el centro de Argentina. En este trabajo se realizaron analisis de parsimonia e inferencia bayesiana para estudiar las relaciones filogeneticas entre las 20 especies de Stenocercus que habitan en los Andes del norte (Ecuador, Colombia y Venezuela), utilizando datos morfologicos y moleculares por separado y en combinacion. Los analisis dieron como resultado topologias similares indicando que las especies de Stenocercus de los Andes del norte estan divididas en 2 clados. Uno contiene 6 especies distribuidas entre el sur de Ecuador y sur de Colombia, mientras que el otro tiene 13 especies distribuidas desde el sur de Ecuador hasta el norte de Colombia y Venezuela. Los resultados tambien sugieren que la reciente formacion de los Andes del norte ha tenido gran influencia sobre la evolucion de Stenocercus.
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phylogeny and biogeography of a large radiation of andean lizards iguania stenocercus
Zoologica Scripta, 2007Co-Authors: Omar TorrescarvajalAbstract:With 61 species occurring mostly in the Andes and adjacent lowland areas, Stenocercus lizards represent one of the most widespread and well-represented Andean vertebrate groups. Phylogenetic relationships among species of Stenocercus are inferred using different datasets based on mitochondrial DNA sequence data of 35 species and morphological data of 59 species. Among morphological data, polymorphic and meristic/morphometric characters are coded under the frequency parsimony and gap-weighting methods, respectively, and the accuracy of these methods is tested. When both types of characters are included, the resulting tree topology is more similar to the topologies obtained from analyses of DNA sequence data than those topologies obtained after exclusion of one or both types of characters. The phylogenetic hypotheses inferred including 59 species of Stenocercus (dataset 1) and excluding those species for which DNA data were not available (dataset 2) are generally congruent with each other, as well as with previously published hypotheses. The most parsimonious tree obtained from analysis of dataset 2 is used in a dispersal-vicariance analysis to infer ancestral areas and major biogeographical events. Species of Stenocercus are divided into two major clades. Clade A has diversified mostly in the central Andes, with a few species in the northern Andes and one species in the southern Andes. Clade B is more widespread, with species in the northern, central, and southern Andes, as well as in the Atlantic lowlands and Amazon basin. The most recent common ancestor of Stenocercus is inferred to have occurred in the eastern cordillera of the central Andes. Given morphological similarity and altitudinal distribution of some species nested in a northern-Andes clade, as well as the relatively recent uplift of this Andean region, it is possible that species in this clade have diverged as recently as the mid-Pliocene.
Arturo E. Corte - One of the best experts on this subject based on the ideXlab platform.
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Chronostratigraphic correlations of cryogenic and glacigenic episodes in central Andes with patagonia
Permafrost and Periglacial Processes, 1991Co-Authors: Arturo E. CorteAbstract:The stratigraphy of cryogenic and glacigenic episodes recorded in Central Andes at latitude 33o south is compared with the magnetostratigraphy of five (I-V) main Patagonian glaciations. Most of the Central Andes cold episodes are relatively dated. A much older event (≈ 2.3 × 106 years BP) is needed to explain the oldest and largest Central Andes glaciation, the sediments of which are tectonically deformed. This is the beginning of climatic change in the Central Andes. Ice-wedge casts in till formed 3.5 × 106 years BP in southern Patagonia are related to an even older cold episode. La stratigraphie des episodes cryogeniques et glaciaires enregistres dans les Andes Centrales a la latitude de 33oS est comparee avec la magnetostratigraphie des cinq (I-V) principales glaciations de Patagonie. La majorite des episodes froids des Andes Centrales sont raccordes avec les glaciations. Un evenement beaucoup plus vieux (± 2,3 millions d'annees BP) est necessaire pour rendre compte de la glaciation le plus vieille et la plus etendue des Andes Centrales, glaciation dont les sediments ont subi des deformations tectoniques. A ce moment, s'est produit le debut du changement climatique dans les Andes Centrales. Des pseudomorphoses de fentes de gel a remplissage de glace formees dans des tills, il y a 3.5 millions d'annees BP dans la Patagonie meridionale sont a mettre en relation avec un episode froid encore plus ancien.
Dussaillant Inés - One of the best experts on this subject based on the ideXlab platform.
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Contribution récente des glaciers des Andes à la ressource en eau et à la hausse du niveau marin : apport des observations satellitaires
HAL CCSD, 2019Co-Authors: Dussaillant InésAbstract:Andean glaciers are amongst the fastest shrinking and the largest contributors to sea level rise in the world. They also represent crucial water resources in the vast semi-arid portions of this large Andes Cordillera (10°N-56°S), sustaining river runoff during dry periods and buffering the effects of droughts. Despite the widespread shrinkage of these glaciers, direct measurement of glacier fluctuations in the Andes are sparse, short-termed and in many cases incomplete, preventing the accurate quantification of recent ice loss for the entire mountain range. Comprehensively quantifying the magnitude of this loss at different special scales is crucial to better constrain future economical, ecological and social impacts. First, we evaluated the performance of a methodology to calculate glacier mass changes on Andean glaciers using time series of digital elevation models (DEMs) derived from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) stereo images. Over our validation zone, the Northern Patagonian Icefield, we found strongly negative icefield-wide mass balance rates of -1.06 ± 0.14 m w.e. yr-1 for the period 2000-2012, in good agreement with estimates from earlier studies and with a second independent estimate (-1.02 ± 0.21 m w.e. yr-1) obtained by differencing the better resolved Shuttle Radar Topography Mission (SRTM) DEM with a Satellite pour l'Observation de la Terre 5 (SPOT5) DEM. Importantly, this work permitted us to (i) validate "ASTER monitoring Ice towards eXtinction" (ASTERIX) method over the Andes; (ii) confirm the lack of penetration of the C-band SRTM radar signal into the NPI snow and firn except for a small high altitude region (above 2900 m a.s.l.) with negligible effects on NPI-wide mass balance; and (iii) provide the basis for an analysis of NPI mass balance changes during different sub-periods between 1975 and 2016 using additional DEMs. Then, we processed more than 30000 ASTER DEMs to calculate the integrated volume of ice lost by Andean glaciers during the past two decades. Andes-wide mass loss amounts to -22.9 ± 5.9 Gt yr-1 (-0.72 ± 0.22 m w.e. yr-1) for the entire period (or -26.0 ± 6.0 Gt yr-1 including subaqueous losses). All regions show consistent glacier wastage, with the most negative mass balance rates in the Patagonian Andes (-0.78 ± 0.25 m w.e. yr-1) and Tropical Andes (-0.42 ± 0.24 m w.e. yr-1). Relatively moderate loss (-0.28 ± 0.18 m w.e. yr-1) is measured in the intermediate regions of the Dry Andes. The inter-decadal patterns of glacier mass loss is an important contribution of this work, observed for the first time at an Andes-wide scale. We observe steady thinning rates in the Tropics and south of 45°S. Conversely, glaciers from the Dry Andes were stable during the 2000s, shifting to drastic thinning rates during the 2010s, coinciding with conditions of sustained drought since 2010. The evaluation of the imbalanced glacier contribution to river discharge during these two decades revealed that glaciers partially helped to mitigate the negative impacts of this sustained drought in the Dry Andes. The results obtained in this thesis contribute to the understanding of recent Andean glacier evolution at a local, regional and Andes-wide scale. We provide a high-quality, multi-decadal dataset that will be useful to constrain the diversity of present 21st century Andes-wide mass loss estimates, in the pursuit of the good calibration of glaciological and hydrological models intended to project future glacier changes and to improve water resource management in the Andes.Les glaciers Andins présentent des taux de recul parmi les plus importants au monde, et contribuent à la hausse du niveau des mers. Ils constituent aussi des ressources en eau vitales pour les vastes zones semi-arides le long de la Cordillère des Andes (10°N-56°S), en alimentant les rivières lors des sécheresses. En dépit du retrait des glaciers Andins, les mesures directes des fluctuations glaciaires sont éparses, de court terme, incomplètes, et ne permettent donc pas une estimation précise de la perte de glace récente à l'échelle de la chaîne entière. Décrire quantitativement cette perte à différentes échelles spatio-temporelle est cruciale afin de mieux anticiper les impacts écologiques, économiques et sociaux. Premièrement, nous avons évalué la performance d'une méthode visant à calculer les changements de masse des glaciers Andins. Cette méthode utilise les séries temporelles des modèles numériques de terrain (DEM) produit par des images stéréoscopiques Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). Sur la zone de validation de la méthode, le Champ de Glace Nord de Patagonie (NPI), nous avons observé un bilan de masse fortement négatif de -1.06 ± 0.14 m w.e. a-1 pour la période 2000-2012. Ces résultats sont cohérent avec les estimations faites précédemment, mais aussi avec une seconde estimation (-1.02 ± 0.21 m w.e. a-1) obtenue indépendamment par différentiation de DEMs de meilleur résolution, Shuttle Radar Topography Mission (SRTM) et Satellite pour l'Observation de la Terre 5 (SPOT5). Ce travail nous a permis de (i) valider la méthode appelée " ASTER monitoring Ice towards eXtinction " (ASTERIX) sur la totalité des Andes, (ii) confirmer l'absence de pénétration du signal radar SRTM dans la bande C sur la neige du NPI (sauf pour une petite région au dessus de 2900 m a.s.l) avec des effets négligeables sur le bilan de masse du NPI; et enfin (iii) fournir la base de travail pour une analyse des variations du bilan de masse du NPI durant différentes sous périodes entre 1975 et 2016, grâce à des DEMs supplémentaires. Ensuite, nous avons généré plus de 30000 DEMs ASTER afin de calculer la perte de l'intégralité des glaciers Andins, et ce pour les deux dernières décennies. La perte de masse à l'échelle des Andes s'élève ainsi à -22.9 ± 5.9 Gt a-1 (-0.72 ± 0.22 m w.e. a-1) pour la période d'étude entière, ou -26.0 ± 6.0 Gt a-1 en incluant les pertes subaquatiques. Toutes les régions affichent une diminution du volume de glace. Les taux les plus négatifs sont observés dans les Andes Patagoniennes (-0.78 ± 0.25 m w.e. a-1) et dans les Andes Tropicales (-0.42 ± 0.24 m w.e. a-1). Les pertes sont modérées dans les régions intermédiaires des Andes Arides (-0.28 ± 0.18 m w.e. a-1). Pour la première fois à l'échelle des Andes, une tendance inter-décennale de la perte volumique a été mise en évidence. Les taux d'amincissement des glaciers tropicaux et ceux situé sous 45°S sont négatifs et stables sur la période considérée. Cependant, alors que les glaciers des Andes arides sont proche de l'équilibre dans les années 2000, leur taux d'amincissement augmentent drastiquement à partir de 2010, coïncident ainsi avec une période de sécheresse intense depuis 2010. L'étude des contributions des pertes de masse décennales des glaciers aux débits des rivières révèle que la fonte de ces glaciers a en partie aidé à minimiser les impacts négatifs de cette sécheresse dans les Andes arides. Les résultats obtenus au cours de cette thèse apportent une meilleure compréhension des pertes récentes des glaciers Andins, localement et régionalement
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Spaceborne monitoring of the recent contribution of glaciers from the Andes to water resources and sea level rise
2019Co-Authors: Dussaillant InésAbstract:Les glaciers Andins présentent des taux de recul parmi les plus importants au monde, et contribuent à la hausse du niveau des mers. Ils constituent aussi des ressources en eau vitales pour les vastes zones semi-arides le long de la Cordillère des Andes (10°N-56°S), en alimentant les rivières lors des sécheresses. En dépit du retrait des glaciers Andins, les mesures directes des fluctuations glaciaires sont éparses, de court terme, incomplètes, et ne permettent donc pas une estimation précise de la perte de glace récente à l'échelle de la chaîne entière. Décrire quantitativement cette perte à différentes échelles spatio-temporelle est cruciale afin de mieux anticiper les impacts écologiques, économiques et sociaux. Premièrement, nous avons évalué la performance d'une méthode visant à calculer les changements de masse des glaciers Andins. Cette méthode utilise les séries temporelles des modèles numériques de terrain (DEM) produit par des images stéréoscopiques Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). Sur la zone de validation de la méthode, le Champ de Glace Nord de Patagonie (NPI), nous avons observé un bilan de masse fortement négatif de -1.06 ± 0.14 m w.e. a-1 pour la période 2000-2012. Ces résultats sont cohérent avec les estimations faites précédemment, mais aussi avec une seconde estimation (-1.02 ± 0.21 m w.e. a-1) obtenue indépendamment par différentiation de DEMs de meilleur résolution, Shuttle Radar Topography Mission (SRTM) et Satellite pour l'Observation de la Terre 5 (SPOT5). Ce travail nous a permis de (i) valider la méthode appelée " ASTER monitoring Ice towards eXtinction " (ASTERIX) sur la totalité des Andes, (ii) confirmer l'absence de pénétration du signal radar SRTM dans la bande C sur la neige du NPI (sauf pour une petite région au dessus de 2900 m a.s.l) avec des effets négligeables sur le bilan de masse du NPI; et enfin (iii) fournir la base de travail pour une analyse des variations du bilan de masse du NPI durant différentes sous périodes entre 1975 et 2016, grâce à des DEMs supplémentaires. Ensuite, nous avons généré plus de 30000 DEMs ASTER afin de calculer la perte de l'intégralité des glaciers Andins, et ce pour les deux dernières décennies. La perte de masse à l'échelle des Andes s'élève ainsi à -22.9 ± 5.9 Gt a-1 (-0.72 ± 0.22 m w.e. a-1) pour la période d'étude entière, ou -26.0 ± 6.0 Gt a-1 en incluant les pertes subaquatiques. Toutes les régions affichent une diminution du volume de glace. Les taux les plus négatifs sont observés dans les Andes Patagoniennes (-0.78 ± 0.25 m w.e. a-1) et dans les Andes Tropicales (-0.42 ± 0.24 m w.e. a-1). Les pertes sont modérées dans les régions intermédiaires des Andes Arides (-0.28 ± 0.18 m w.e. a-1). Pour la première fois à l'échelle des Andes, une tendance inter-décennale de la perte volumique a été mise en évidence. Les taux d'amincissement des glaciers tropicaux et ceux situé sous 45°S sont négatifs et stables sur la période considérée. Cependant, alors que les glaciers des Andes arides sont proche de l'équilibre dans les années 2000, leur taux d'amincissement augmentent drastiquement à partir de 2010, coïncident ainsi avec une période de sécheresse intense depuis 2010. L'étude des contributions des pertes de masse décennales des glaciers aux débits des rivières révèle que la fonte de ces glaciers a en partie aidé à minimiser les impacts négatifs de cette sécheresse dans les Andes arides. Les résultats obtenus au cours de cette thèse apportent une meilleure compréhension des pertes récentes des glaciers Andins, localement et régionalement.Andean glaciers are amongst the fastest shrinking and the largest contributors to sea level rise in the world. They also represent crucial water resources in the vast semi-arid portions of this large Andes Cordillera (10°N-56°S), sustaining river runoff during dry periods and buffering the effects of droughts. Despite the widespread shrinkage of these glaciers, direct measurement of glacier fluctuations in the Andes are sparse, short-termed and in many cases incomplete, preventing the accurate quantification of recent ice loss for the entire mountain range. Comprehensively quantifying the magnitude of this loss at different special scales is crucial to better constrain future economical, ecological and social impacts. First, we evaluated the performance of a methodology to calculate glacier mass changes on Andean glaciers using time series of digital elevation models (DEMs) derived from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) stereo images. Over our validation zone, the Northern Patagonian Icefield, we found strongly negative icefield-wide mass balance rates of -1.06 ± 0.14 m w.e. yr-1 for the period 2000-2012, in good agreement with estimates from earlier studies and with a second independent estimate (-1.02 ± 0.21 m w.e. yr-1) obtained by differencing the better resolved Shuttle Radar Topography Mission (SRTM) DEM with a Satellite pour l'Observation de la Terre 5 (SPOT5) DEM. Importantly, this work permitted us to (i) validate "ASTER monitoring Ice towards eXtinction" (ASTERIX) method over the Andes; (ii) confirm the lack of penetration of the C-band SRTM radar signal into the NPI snow and firn except for a small high altitude region (above 2900 m a.s.l.) with negligible effects on NPI-wide mass balance; and (iii) provide the basis for an analysis of NPI mass balance changes during different sub-periods between 1975 and 2016 using additional DEMs. Then, we processed more than 30000 ASTER DEMs to calculate the integrated volume of ice lost by Andean glaciers during the past two decades. Andes-wide mass loss amounts to -22.9 ± 5.9 Gt yr-1 (-0.72 ± 0.22 m w.e. yr-1) for the entire period (or -26.0 ± 6.0 Gt yr-1 including subaqueous losses). All regions show consistent glacier wastage, with the most negative mass balance rates in the Patagonian Andes (-0.78 ± 0.25 m w.e. yr-1) and Tropical Andes (-0.42 ± 0.24 m w.e. yr-1). Relatively moderate loss (-0.28 ± 0.18 m w.e. yr-1) is measured in the intermediate regions of the Dry Andes. The inter-decadal patterns of glacier mass loss is an important contribution of this work, observed for the first time at an Andes-wide scale. We observe steady thinning rates in the Tropics and south of 45°S. Conversely, glaciers from the Dry Andes were stable during the 2000s, shifting to drastic thinning rates during the 2010s, coinciding with conditions of sustained drought since 2010. The evaluation of the imbalanced glacier contribution to river discharge during these two decades revealed that glaciers partially helped to mitigate the negative impacts of this sustained drought in the Dry Andes. The results obtained in this thesis contribute to the understanding of recent Andean glacier evolution at a local, regional and Andes-wide scale. We provide a high-quality, multi-decadal dataset that will be useful to constrain the diversity of present 21st century Andes-wide mass loss estimates, in the pursuit of the good calibration of glaciological and hydrological models intended to project future glacier changes and to improve water resource management in the Andes
Herman Silva - One of the best experts on this subject based on the ideXlab platform.
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Biogeography, phylogenetic relationships and morphological analyses of the South American genus Mutisia L.f. (Asteraceae) shows early connections of two disjunct biodiversity hotspots
Organisms Diversity & Evolution, 2020Co-Authors: Andrés Moreira-muñoz, Rosa A. Scherson, Federico Luebert, María José Román, Marcelo Monge, Mauricio Diazgranados, Herman SilvaAbstract:The Andes is recognized as one of the most biodiverse places on Earth, promoting in its uplift process a series of recent rapid diversification events in different biotic groups like birds, mammals, insects and vascular plants. The uplift of the Andes during the Cenozoic acted as a barrier for many biotic groups, as a scenario for radiation processes due to occupancy of different niches and as a corridor for others. Connections between the Andes and the Atlantic Forest showed intermittent phases along the Cenozoic, affecting the distribution patterns and diversification of different biotic groups. Nowadays, the Andes and the Atlantic Forest are both considered globally relevant biodiversity hotspots. Floristic groups thriving in both hotspots are crucial for a better understanding of their biogeographic history, as well as for informing future conservation actions. Mutisia (Asteraceae), a genus comprising 63 perennial shrubs and vines endemic to South America, shows a marked West-East disjunction: Most species occupy almost the whole Andean chain from Colombia to Patagonia, while a second group encompasses four species distributed in eastern Brazil and the surrounding areas of Paraguay, Uruguay and Argentina. We reconstructed the phylogeny of the genus to assess its possible biogeographic history. We analysed three DNA regions, i.e. the chloroplast trnL-trnF intergenic spacer and the nuclear ribosomal internal and external transcribed spacers, ITS and ETS. Using maximum likelihood and Bayesian inference, gene trees were reconstructed, and a concatenated phylogenetic tree was inferred. Divergence times were estimated by means of BEAST, and the ancestral areas were inferred using BioGeoBEARS. An ancestral reconstruction of morphological traits was also performed, as well as maps representing current richness hotspots within the genus. Phylogenetic analyses strongly support the monophyly of Mutisia , with two well-supported main clades: clade A, with presence of Atlantic-central-northern Andes species, and clade B, with central/southern Andes species. Dating analyses suggest that a main clade separation occurred at the early Miocene, followed by the separation of the Atlantic clade A2 by the late Miocene, and more recent radiations occurred in the central, northern and southern Andes during the Pliocene. Results are in tune with other angiosperm taxa that also underwent rapid radiations, possibly related to environmental and pollinator changes. The biogeographic history of Mutisia is related to morphological adaptations, history and geographic factors acting since the Miocene along the Andes and adjacent areas. Threat assessments and conservation actions for the genus shall include the whole distribution range, including low-range northern and southern Andes species, as well as the distinctive Atlantic Forest clade.
Nicolás Huneeus - One of the best experts on this subject based on the ideXlab platform.
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Pathways for wintertime deposition of anthropogenic light-absorbing particles on the Central Andes cryosphere
Environmental Pollution, 2020Co-Authors: Rémy Lapere, Sylvain Mailler, Laurent Menut, Nicolás HuneeusAbstract:Ice and snow in the Central Andes contain significant amounts of light-absorbing particles such as black carbon. The consequent accelerated melting of the cryosphere is not only a threat from a climate perspective but also for water resources and snow-dependent species and activities, worsened by the mega-drought affecting the region since the last decade. Given its proximity to the Andes, emissions from the Metropolitan Area of Santiago, Chile, are believed to be among the main contributors to deposition on glaciers. However, no evidence backs such an assertion, especially given the usually subsident and stable conditions in wintertime, when the snowpack is at its maximum extent. Based on high-resolution chemistry-transport modeling with WRF-CHIMERE, the present work shows that, for the month of June 2015, up to 40% of black carbon dry deposition on snow or ice covered areas in the Central Andes downwind from the Metropolitan area can be attributed to emissions from Santiago. Through the analysis of aerosol tracers we determine (i) that the areas of the Metropolitan Area where emissions matter most when it comes to export towards glaciers are located in Eastern Santiago near the foothills of the Andes, (ii) the crucial role of the network of Andean valleys that channels pollutants up to remote locations near glaciers, following gentle slopes. A direct corollary is that severe urban pollution, and deposition of impurities on the Andes, are anti-correlated phenomena. Finally, a two-variable meteorological index is developed that accounts for the dynamics of aerosol export towards the Andes, based on the zonal wind speed over the urban area, and the vertical diffusion coefficient in the valleys close to ice and snow covered terrain. Numerous large urban areas are found along the Andes so that the processes studied here can shed light on similar investigations for other glaciers-dependent Andean regions.
