ABSTRACT
Resumen: Presentación del caso: Paciente femenino de 2 años de edad con malformación Anorrectal y fístula rectovestibular a quién se realizó colostograma distal con sulfato de bario provocando concreción lítica de bario en el fondo de saco del colon distal al no enjuagar el contenido. Ante la imposibilidad de retirar el enterolito a través del estoma disfuncional de la derivación intestinal decidimos realizar la extracción al momento de hacer la anorrectoplastía sagital posterior con riesgo aumentado de infección, dehiscencia de herida y lesión de estructuras adyacentes. Enfatizamos la necesidad de recordar a la comunidad médica radiológica y pediátrica de la adecuada realización de este tipo de estudios siempre con medio de contraste hidrosoluble, y aprovechamos para recapitular la técnica de realización del mismo.
Abstract: Case presentation: 2 year-old female patient with anorectal malformation with recto-vestibular fistula to whom a distal colostogram with barium sulfate was done, thus provoking lithic concretion in the distal sac. Since it was deemed impossible to extract the enterolith trough de distal stoma we decided to perform the anorectoplasty and extract the lit at that moment knowing the increased surgical risks such as infection, dehiscence and damage of adjacent structures. We stress the need to remind the radiological and pediatric medical communities to always perform this kind of imaging studies with water-soluble contrast agents and we also annotate the technique for doing so.
ABSTRACT
Identifying factors that may be responsible for regulating the size of animal populations is a cornerstone in understanding population ecology. The main factors that are thought to influence population size are either resources (bottom-up), or predation (top-down), or interspecific competition (parallel). However, there are highly variable and often contradictory results regarding their relative strengths and influence. These varied results are often interpreted as indicating "shifting control" among the three main factors, or a complex, nonlinear relationship among environmental variables, resource availability, predation, and competition. We argue here that there is a "missing link" in our understanding of predator-prey dynamics. We explore whether the landscape-of-fear model can help us clarify the inconsistencies and increase our understanding of the roles, extent, and possible interactions of top-down, bottom-up, and parallel factors on prey population abundance. We propose two main predictions derived from the landscape-of-fear model: (1) for a single species, we suggest that as the makeup of the landscape of fear changes from relatively safe to relatively risky, bottom-up impacts switch from strong to weak as top-down impacts go from weak to strong; (2) for two or more species, interspecific competitive interactions produce various combinations of bottom-up, top-down, and parallel impacts depending on the dominant competing species and whether the landscapes of fear are shared or distinctive among competing species. We contend that these predictions could successfully explain many of the complex and contradictory results of current research. We test some of these predictions based on long-term data for small mammals from the Chihuahuan Desert in the United States, and Mexico. We conclude that the landscape-of-fear model does provide reasonable explanations for many of the reported studies and should be tested further to better understand the effects of bottom-up, top-down, and parallel factors on population dynamics.
