No abstract

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.

Investigation of tree growth in Isle Royale National Park in Michigan revealed the influence of herbivores and carnivores on plants in an intimately linked food chain. Plant growth rates were regulated by cycles in animal density and responded to annual changes in primary productivity only when released from herbivory by wolf predation. Isle Royale's dendrochronology complements a rich literature on food chain control in aquatic systems, which often supports a trophic cascade model. This study provides evidence of top-down control in a forested ecosystem.

The observation that small isolated populations often suffer reduced fitness from inbreeding depression has guided conservation theory and practice for decades. However, investigating the genome-wide dynamics associated with inbreeding depression in natural populations is only now feasible with relatively inexpensive sequencing technology and annotated reference genomes. To characterize the genome-wide effects of intense inbreeding and isolation, we performed whole-genome sequencing and morphological analysis of an iconic inbred population, the gray wolves (Canis lupus) of Isle Royale. Through population genetic simulations and comparison with wolf genomes from a variety of demographic histories, we find evidence that severe inbreeding depression in this population is due to increased homozygosity of strongly deleterious recessive mutations. Our results have particular relevance in light of the recent translocation of wolves from the mainland to Isle Royale, as well as broader implications for management of genetic variation in the fragmented landscape of the modern world.

Summary1. For large predators living in seasonal environments, patterns of predation are likely to vary among seasons because of related changes in prey vulnerability. Variation in prey vulnerability underlies the influence of predators on prey populations and the response of predators to seasonal variation in rates of biomass acquisition. Despite its importance, seasonal variation in predation is poorly understood. 2. We assessed seasonal variation in prey composition and kill rate for wolves Canis lupus living on the Northern Range (NR) of Yellowstone National Park. Our assessment was based on data collected over 14 winters (1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)) and five spring-summers between 2004 and 2009. 3. The species composition of wolf-killed prey and the age and sex composition of wolf-killed elk Cervus elaphus (the primary prey for NR wolves) varied among seasons. 4. One's understanding of predation depends critically on the metric used to quantify kill rate. For example, kill rate was greatest in summer when quantified as the number of ungulates acquired per wolf per day, and least during summer when kill rate was quantified as the biomass acquired per wolf per day. This finding contradicts previous research that suggests that rates of biomass acquisition for large terrestrial carnivores tend not to vary among seasons. 5. Kill rates were not well correlated among seasons. For example, knowing that early-winter kill rate is higher than average (compared with other early winters) provides little basis for anticipating whether kill rates a few months later during late winter will be higher or lower than average (compared with other late winters). This observation indicates how observing, for example, higherthan-average kill rates throughout any particular season is an unreliable basis for inferring that the year-round average kill rate would be higher than average. 6. Our work shows how a large carnivore living in a seasonal environment displays marked seasonal variation in predation because of changes in prey vulnerability. Patterns of wolf predation were influenced by the nutritional condition of adult elk and the availability of smaller prey (i.e. elk calves, deer). We discuss how these patterns affect our overall understanding of predator and prey population dynamics.