BackgroundContagious prion diseases – scrapie of sheep and chronic wasting disease of several species in the deer family – give rise to epidemics that seem capable of compromising host population viability. Despite this prospect, the ecological consequences of prion disease epidemics in natural populations have received little consideration.Methodology/Principal FindingsUsing a cohort study design, we found that prion infection dramatically lowered survival of free-ranging adult (>2-year-old) mule deer (Odocoileus hemionus): estimated average life expectancy was 5.2 additional years for uninfected deer but only 1.6 additional years for infected deer. Prion infection also increased nearly fourfold the rate of mountain lions (Puma concolor) preying on deer, suggesting that epidemics may alter predator–prey dynamics by facilitating hunting success. Despite selective predation, about one fourth of the adult deer we sampled were infected. High prevalence and low survival of infected deer provided a plausible explanation for the marked decline in this deer population since the 1980s.ConclusionRemarkably high infection rates sustained in the face of intense predation show that even seemingly complete ecosystems may offer little resistance to the spread and persistence of contagious prion diseases. Moreover, the depression of infected populations may lead to local imbalances in food webs and nutrient cycling in ecosystems in which deer are important herbivores.

Resumen. Se sabe que los adultos de varias especies de Paseriformes del oeste de América del Norte migran a la región monzónica de México para mudar desde julio hasta octubre antes de continuar con la migración hacia sus áreas de invernada en el Neotrópico. Sin embargo, se sabe poco sobre la biología y los requerimientos de hábi-tat de estas aves en sus áreas de muda. Por lo tanto, establecimos 13 estaciones de anillado durante las estaciones monzónicas de 2007 y 2008 en el sudeste de Arizona, centro de Sonora y centro de Sinaloa. Estudiamos la ocurrencia espacial y temporal de 10 especies previamente conocidas y de 9 especies nuevas que mudan en los sitios de muda migratoria. En muchas de estas especies, la mayoría o todos los individuos migran hacia sitios en que comienzan la muda, pero en otras, esta migración hacia los sitios de muda parece estar limitada a una proporción pequeña de la población, enfatizando la necesidad de definir la migración para muda al nivel del individuo más que al de la población. Nuestros resultados sugieren que durante la estación monzónica seca de 2007, los migrantes en muda buscaron hábitats ribereños, mientras que en la estación más húmeda de 2008, cuando la expansión de la vegetación fue mayor, éstos estuvieron más ampliamente distribuidos en los hábitats secos. La fidelidad de sitio a las áreas de TEMPORAL, SPATIAL, AND ANNUAL VARIATION IN ThE OCCURRENCE Of MOLT-MIgRANT PASSERINES IN ThE MExICAN MONSOON REgION Variación Temporal, Espacial y Anual en la Presencia de Aves Paseriformes Migratorias durante la Etapa de Muda en la Región Monzónica MexicanaAbstract. Adults of several species of western North American passerines are known to migrate to the Mexican monsoon region to undergo molt from July to October before continuing migration to their wintering grounds in the neotropics, but little is known about the biology and habitat requirements of these birds on their molting grounds. Therefore we established 13 banding stations during the monsoon seasons of 2007 and 2008 in southeastern Arizona, central Sonora, and central Sinaloa. We studied the spatial and temporal occurrence of 10 previously known and 9 new species of molt migrants on the molting grounds. In many of these species most or all individuals appeared to undertake molt migration but in others it appeared to be limited to a small proportion of the population, underscoring that molt migration must be defined at the level of the individual rather than of the population. Our results suggest that during the drier 2007 monsoon season molt migrants sought out riparian habitats, whereas in the wetter 2008 season, when the flush of vegetation was greater, they were more widely distributed in drier habitats. Site fidelity to molting grounds was virtually zero, significantly less than site fidelity to banding stations on breeding and winter grounds. Our results suggest that molt migration to the Mexican monsoon region is a stochastic or plastic process, substantially influenced by individual choices related to variation in weat...

Human activity influences wildlife populations and activity patterns: implications for spatial and temporal refuges.

No abstract

ABSTRACT:Chronic wasting disease (CWD), a prion disease of mule deer (Odocoileus hemionus), accelerates mortality and in so doing has the potential to influence population dynamics. Although effects on mule deer survival are clear, how CWD affects recruitment is less certain. We studied how prion infection influenced the number of offspring raised to weaning per adult ($2 yr old) female mule deer and subsequently the estimated growth rate (l) of an infected deer herd. Infected and presumably uninfected radio-collared female deer were observed with their fawns in late summer (August-September) during three consecutive years (2006)(2007)(2008) in the Table Mesa area of Boulder, Colorado, USA. We counted the number of fawns accompanying each female, then used a fully Bayesian model to estimate recruitment by infected and uninfected females and the effect of the disease on l. On average, infected females weaned 0.95 fawns (95% credible interval50.56-1.43) whereas uninfected females weaned 1.34 fawns (95% credible interval51.09-1.61); the probability that uninfected females weaned more fawns than infected females was 0.93). We used estimates of prevalence to weight recruitment and survival parameters in the transition matrix of a three-age, single-sex matrix model and then used the matrix to calculate effects of CWD on l. When effects of CWD on both survival and recruitment were included, the modeled l was 0.97 (95% credible interval 5 0.82-1.09). Effects of disease on l were mediated almost entirely by elevated mortality of infected animals. We conclude that although CWD may affect mule deer recruitment, these effects seem to be sufficiently small that they can be omitted in estimating the influences of CWD on population growth rate.