Determining population sizes can be difficult, but is essential for conservation. By counting distinct microsatellite genotypes, DNA from noninvasive samples (hair, faeces) allows estimation of population size. Problems arise because genotypes from noninvasive samples are error-prone, but genotyping errors can be reduced by multiple polymerase chain reaction (PCR). For faecal genotypes from wolves in Yellowstone National Park, error rates varied substantially among samples, often above the 'worst-case threshold' suggested by simulation. Consequently, a substantial proportion of multilocus genotypes held one or more errors, despite multiple PCR. These genotyping errors created several genotypes per individual and caused overestimation (up to 5.5-fold) of population size. We propose a 'matching approach' to eliminate this overestimation bias.
The effect of human activities on animal populations is widely debated, particularly since a recent decision by the U.S. Department of the Interior to ban snowmobiles from national parks. Immunoassays of fecal glucocorticoid levels provide a sensitive and noninvasive method of measuring the physiological stress responses of wildlife to disturbances. We tested for associations between snowmobile activity and glucocorticoid levels in an elk ( Cervus elaphus ) population in Yellowstone National Park and wolf ( Canis lupus ) populations in Yellowstone, Voyageurs, and Isle Royale national parks. For wolves, comparisons among populations and years showed that fecal glucocorticoid levels were higher in areas and times of heavy snowmobile use. For elk, day-to-day variation in fecal glucocorticoid levels paralleled variation in the number of snowmobiles after we controlled for the effects of weather and age. Also for elk, glucocorticoid concentrations were higher in response to snowmobiles than to wheeled vehicles after we controlled for the effects of age, weather, and number of vehicles. Despite these stress responses, there was no evidence that current levels of snowmobile activity are affecting the population dynamics of either species in these locations.
Actividad de Vehículos para Nieve y Respuestas de Stress Glucocorticoide en Lobos y AlcesResumen: El efecto de actividades humanas sobre poblaciones animales es ampliamente debatido, particularmente desde una reciente decisión del Departamento del Interior de EE.UU. de prohibir los vehículos para nieve en los Parques Nacionales. Inmunoensayos de los niveles glucocorticoides fecales proporcionan un método sensible y no invasivo para medir respuestas de stress fisiológico de fauna silvestre a disturbios. Probamos las asociación entre la actividad de vehículos de nieve y niveles de glucocorticoides en una población de alces ( Cervus elaphus ) en el Parque Nacional Yellowstone y en poblaciones de lobos ( Canis lupus ) en los parques nacionales Yellowstone, Voyageurs e Isle Royale. Para lobos, las comparaciones entre poblaciones y años mostraron que los niveles de glucocorticoides fecales son mayores en áreas y tiempos de intenso uso de vehículos para nieve. Para alces, la variación diaria de los niveles de glucocorticoides fecales fue paralela a la variación en el número de vehículos para nieve después de controlar para efectos del clima y la edad. También para alces, las concentraciones de glucocorticoides fueron mayores en respuesta a los vehículos para nieve que en respuesta a vehículos de ruedas después de controlar para los efectos de la edad, el clima y el número de vehículos. A pesar de estas respuestas al stress, no hubo evidencia de que los niveles de actividad de vehículos para nieve afecten la dinámica poblacional de ninguna de las especies en estas localidades.
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