Browsing by Author "Riquelme, Carlos"

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    Automatic Recognition of Black-Necked Swan (Cygnus melancoryphus) from Drone Imagery
    (2023) Jimenez-Torres, Marina; Silva, Carmen P. P.; Riquelme, Carlos; Estay, Sergio A. A.; Soto-Gamboa, Mauricio
    Ecological monitoring programs are fundamental to following natural-system populational trends. Drones are a new key to animal monitoring, presenting different benefits but two basic re-strictions First, the increase of information requires a high capacity of storage and, second, time invested in data analysis. We present a protocol to develop an automatic object recognizer to minimize analysis time and optimize data storage. We conducted this study at the Cruces River, Valdivia, Chile, using a Phantom 3 Advanced drone with an HD-standard camera. We used a Black-necked swan (Cygnus melancoryphus) as a model because it is abundant and has a contrasting color compared to the environment, making it easy detection. The drone flew 100 m from water surface (correcting AGL in relation to pilot landing altitude) obtaining georeferenced images with 75% overlap and developing approximately 0.69 km(2) of orthomosaics images. We estimated the swans' spectral signature to build the recognizer and adjusted nine criteria for object-oriented classification. We obtained 140 orthophotos classified into three brightness categories. We found that the Precision, Sensitivity, Specificity, and Accuracy indicator were higher than 0.93 and a calibration curve with R2= 0.991 for images without brightness. The recognizer prediction decreases with brightness but is corrected using ND8-16 filter lens. We discuss the importance of this recognizer to data analysis optimization and the advantage of using this recognition protocol for any object in ecological studies.
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    Exploring the influence of density-dependence and weather on the spatial and temporal variation in common vole (Microtus arvalis) abundance in Castilla y León, NW Spain
    (2024) Caminero-Saldana, Constantino; Correa-Cuadros, Jennifer Paola; Banos-Herrero, Ana; Riquelme, Carlos; Pallavicini, Yesica; Fernandez-Villan, Mercedes; Plaza, Javier; Perez-Sanchez, Rodrigo; Sanchez, Nilda; Mougeot, Francois; Luque-Larena, Juan Jose; Jaksic, Fabian M.; Garcia-Ariza, Maria Carmen
    BACKGROUND: The common vole has invaded the agroecosystems of northwestern Spain, where outbreaks cause important crop damage and management costs. Little is yet known about the factors causing or modulating vole fluctuations. Here, we used 11 years of vole abundance monitoring data in 40 sites to study density-dependence and weather influence on vole dynamics. Our objective was to identify the population dynamics structure and determine whether there is direct or delayed density-dependence. An evaluation of climatic variables followed, to determine whether they influenced vole population peaks. RESULTS: First- and second-order outbreak dynamics were detected at 7 and 33 study sites, respectively, together with second-order variability in periodicity (2-3 to 4-5-year cycles). Vole population growth was explained by previous year abundance (mainly numbers in summer and spring) at 21 of the sites (52.5%), by weather variables at 11 sites (27.5%; precipitation or temperature in six and five sites, respectively), and by a combination of previous abundance and weather variables in eight sites (20%). CONCLUSIONS: We detected variability in vole spatiotemporal abundance dynamics, which differs in cyclicity and period. We also found regional variation in the relative importance of previous abundances and weather as factors modulating vole fluctuations. Most vole populations were cyclical, with variable periodicity across the region. Our study is a first step towards the development of predictive modeling, by disclosing relevant factors that might trigger vole outbreaks. It improves decision-making processes within integrated management dealing with mitigation of the agricultural impacts caused by voles. (c) 2023 Society of Chemical Industry.
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    Extinction risk assessment of a Patagonian ungulate using population dynamics models under climate change scenarios
    (2020) Riquelme, Carlos; Estay, Sergio A.; Contreras, Rafael; Corti, Paulo
    Climate change affects population cycles of several species, threatening biodiversity. However, there are few long-term studies on species with conservation issues and restricted distributions. Huemul is a deer endemic to the southern Andes in South America and it is considered endangered mostly due to a 50% reduction of its distribution over the last 500 years. To assess environmental variables potentially affecting huemul population viability and the impact of climate change, we developed population dynamics models. We used a 14-year survey data from Bernardo O'Higgins National Park, coastal Chilean Patagonia. We used Ricker models considering winter and spring temperatures and precipitation as variables influencing huemul population dynamics. We used the Bayesian information criterion (BIC) to select models with the greatest predictive power. The two best models (Delta BIC < 2) included winter temperature and density-dependence population growth drivers. The best model considered a lateral effect, where winter temperature influences carrying capacity and the second best a vertical effect with winter temperature influencingR(max)and carrying capacity. Population viability was evaluated using those models, projecting them over a 100-year period: (a) under current conditions and (b) under conditions estimated by Global Climate Models for 2050 and 2070. The extinction risk and quasi-extinction were estimated for this population considering two critical huemul abundance levels (15 and 30 individuals) for persistence. The population is currently in a quasi-extinction process, with extinction probabilities increasing with climate change. These results are crucial for conservation of species like huemul that have low densities and are threatened by climate change.
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    Out of sight, not out of mind: The effect of access to conservation sites on the willingness to pay for protecting endangered species
    (2024) Henriquez, Makarena; Vasquez-Lavin, Felipe; Barrientos, Manuel; Oliva, Roberto D. Ponce; Lara, Antonio; Flores-Benner, Gabriela; Riquelme, Carlos
    According to the latest global assessment report on biodiversity and ecosystem services, nature and biodiversity have experienced a global decline, making the development of conservation policies urgent. Herein, we used a contingent valuation survey to estimate the economic value of a reintroduction program for the huemul ( Hip- pocamelus bisulcus ), an endangered charismatic species in Chile. Our novel approach exploits changes in the access to the site to disentangle nonuse value from use value. We use parametric and nonparametric models to estimate the willingness to pay for the program. Our findings consistently indicate that the conservation of the huemul is valued more when tourist access is restricted, as opposed to allowing visitors access to reintroduction areas. We also analyze the sensitivity of this main finding to different cut-off points of a certainty scale, showing that the results are robust. We hypothesize that people are willing to pay a "premium" to keep the conservation site "out of sight" from tourist activities. This could also be related to the belief that a reintroduction program would be more effective if access was not allowed. A cost -benefit analysis using the most conservative assumptions suggests that social benefit significantly outperforms cost.
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    Pelvic intravenous leiomyomatosis with intracardiac extension. Report of two cases
    (SOC MEDICA SANTIAGO, 2012) Mertens, Renato; Valdes, Francisco; Munoz, Cecilia; Irarrazaval, Manuel; Branes, Jorge; Riquelme, Carlos; Marine, Leopoldo; Bergoeing, Michel; Kraemer, Albrecht
    Intravenous leiomyomatosis with extension into the heart is an infrequent entity described in 1907. Its clinical presentation is non-specific, although cardiac symptoms predominate. Diagnosis is based on clinical findings and appropriate imaging. We report two females, aged 35 and 51 years. One of them presented with a pelvic mass and dyspnea, the other patient had severe cardiac failure on admission. Computed axial tomography scan allowed an accurate preoperative diagnosis on both patients. Successful one stage resection of the tumor was performed under cardiopulmonary bypass. Both patients are asymptomatic on follow up at 6 months and 25 years. (Rev Med Chile 2012; 140: 906-909).
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    Protected areas' effectiveness under climate change : a latitudinal distribution projection of an endangered mountain ungulate along the Andes Range
    (2018) Riquelme, Carlos; Estay Cabrera, Sergio Andrés; López, Rodrigo; Pastore, Hernán; Soto Gamboa, Mauricio; Corti, Paulo
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    Radiación y medios de contraste en embarazo y lactancia: lo que el clínico necesita saber
    (2022) Riquelme, Carlos; Nesvadba, Annael; Sanhueza, Camila; Garrido Cisterna, Francisco Javier
    Introducción: el uso de técnicas de imagenología es habitual e incluso indispensable en algunos procesos diagnósticos. Sin embargo, su indicación en mujeres embarazadas y en período de lactancia es controvertida. Objetivo: presentar una revisión narrativa sobre los riesgos asociados al uso de imágenes con radiación y medio de contraste en embarazo y periodo de lactancia, con énfasis en las recomendaciones y aplicaciones clínicas que el médico tratante debe tener presente al momento de su indicación. Métodos: se realizó una revisión bibliográfica de la literatura relevante sobre los riesgos y consideraciones especiales del uso de medios de contraste en el embarazo y lactancia. Resultados: los riesgos de la radiación ionizante sobre el feto varían de acuerdo al estadio del embarazo, por lo que la indicación del estudio debe ponderar los riesgos y beneficios. En las dosis clínicas en embarazo y lactancia, el uso de contraste yodado como basados en gadolinio no tienen efectos deletéreos en la salud de la madre ni la del feto. Sin embargo, las sociedades internacionales recomiendan limitar su uso. Conclusión: si bien la indicación de estudios de imagen que utilizan radiación ionizante en el embarazo y lactancia es seguro, el médico clínico debe conocer los posibles riesgos de la radiación ionizante en este grupo de pacientes. Respecto a los medios de contraste, el único efecto adverso reportado es la disfunción tiroidea transitoria en hijos de madres que recibieron medios de contraste yodado.