Climate-induced phenological shifts can influence population, evolutionary, and ecological dynamics, but our understanding of these phenomena is hampered by a lack of long-term demographic data. We ...use a multi-decade census of 5 salmonid species representing 14 life histories in a warming Alaskan stream to address the following key questions about climate change and phenology: How consistent are temporal patterns and drivers of phenology for similar species and alternative life histories? Are shifts in phenology associated with changes in phenotypic variation? How do phenological changes influence the availability of resource subsidies? For most salmonid species, life stages, and life histories, freshwater temperature influences migration timing--migration events are occurring earlier in time (mean = 1.7 days earlier per decade over the 3-5 decades), and the number of days over which migration events occur is decreasing (mean = 1.5 days per decade). Temporal trends in migration timing were not correlated with changes in intra-annual phenotypic variation, suggesting that these components of the phenotypic distribution have responded to environmental change independently. Despite commonalities across species and life histories, there was important biocomplexity in the form of disparate shifts in migration timing and variation in the environmental factors influencing migration timing for alternative life history strategies in the same population. Overall, adult populations have been stable during these phenotypic and environmental changes (λ ≈ 1.0), but the temporal availability of salmon as a resource in freshwater has decreased by nearly 30 days since 1971 due to changes in the median date of migration timing and decreases in intra-annual variation in migration timing. These novel observations advance our understanding of phenological change in response to climate warming, and indicate that climate change has influenced the ecology of salmon populations, which will have important consequences for the numerous species that depend on this resource.
In seasonally varying environments, animals should alter habitat selection through time to avoid the harshest conditions. Winter severity is limiting for many ungulates in high-latitude ecosystems, ...and quality of habitat is an important determinant of winter survival. Previous studies in Southeast Alaska indicated that Sitka black-tailed deer (Odocoileus hemionus sitkensis) selected old-growth forest that provides both snow interception and forage, but with great variability among studies, years, and geographic areas. Clearcut timber harvest has greatly reduced the extent and quality of old-growth forest. The value of 2nd-growth and old-growth forest types to deer likely depends on snow depth, which is highly variable in space and time. We measured selection for vegetation classes, landscape features, and forage biomass by monitoring 56 GPS-radiocollared adult female deer from 1 January to 1 April between 2011 and 2013. Simultaneously, we measured snow depth across deer home ranges daily. We determined that snow depth had a strong effect on selection for vegetation classes. During periods of low snow, deer selected young 2nd growth but avoided old 2nd growth and high-volume old growth. As snow depths increased, young 2nd growth was avoided and deer selected old 2nd-growth and productive old-growth forests. The composition of vegetation classes within the landscape influenced selection, with deer selecting locally abundant habitats. These behaviors suggest that the widespread distribution of forest patches that provide snow interception and forage biomass may be critical to fulfilling the energetic requirements of deer during winters with snow. Such context-dependent habitat selection is likely widespread among wildlife species in variable environments and should be incorporated into study design and analysis.
Understanding the effects of harvest on wildlife populations is fundamental to theoretical wildlife science and applied wildlife management. Demographic compensation plays a key role in models of ...wildlife population dynamics and in developing harvest strategies. The degree and form of compensation in a given population depend on its particular ecological and life‐history characteristics and the timing and magnitude of harvest. Consequently, substantial variation exists in compensatory potential among populations, and it cannot be assumed that a particular population is capable of compensating for harvest. This underscores the importance of population‐specific assessments of responses to harvest. We examined the hypothesis that concentrated hunting pressure in road‐accessible areas reduces subsequent breeding season densities of willow ptarmigan (Lagopus lagopus), in Alaska, USA, 2014–2015. We estimated breeding season densities of ptarmigan territories at sites within hunted access corridors and at remote sites with little or no hunting pressure. Estimated densities were substantially higher at remote sites (5.3–5.8 territories/km2) than at accessible sites (1.8–3.7 territories/km2). Two habitat‐proxy covariates, distance to water and elevation (modeled as smoothed effects), exhibited strong associations with the density of ptarmigan territories. These results suggest a possible additive effect of spatially concentrated harvest on local breeding densities.
We examined the effect that concentrated hunting pressure in road‐accessible areas had on subsequent breeding season densities of a highly valued upland game species, the willow ptarmigan (Lagopus lagopus), in Alaska, USA. Estimated densities were substantially higher at unhunted remote sites (5.3–5.8 territories per km2) than at hunted accessible sites (1.8–3.7 territories per km2), suggesting an additive effect of spatially concentrated harvest on local breeding densities.
Influenza A Viruses (IAV) in nature must overcome shifting transmission barriers caused by the mobility of their primary host, migratory wild birds, that change throughout the annual cycle. Using a ...phylogenetic network of viral sequences from North American wild birds (2008–2011) we demonstrate a shift from intraspecific to interspecific transmission that along with reassortment, allows IAV to achieve viral flow across successive seasons from summer to winter. Our study supports amplification of IAV during summer breeding seeded by overwintering virus persisting locally and virus introduced from a wide range of latitudes. As birds migrate from breeding sites to lower latitudes, they become involved in transmission networks with greater connectivity to other bird species, with interspecies transmission of reassortant viruses peaking during the winter. We propose that switching transmission dynamics may be a critical strategy for pathogens that infect mobile hosts inhabiting regions with strong seasonality.
The effects of hunting on wildlife populations vary dramatically, depending on the timing and magnitude of harvest, and population‐specific states and vital rates. We examined the hypothesis that ...spatially and seasonally concentrated harvest decreases annual survival probabilities of willow ptarmigan (Lagopus lagopus). We estimated survival of radio‐marked willow ptarmigan at 2 categories of sites: those where ptarmigan were easily accessible and heavily hunted and those that were remote and received little or no hunting pressure in Alaska, USA. We predicted that seasonal survival estimates during the willow ptarmigan hunting season would be lower in access corridors than at remote sites and that this would result in lower annual survival unless subsequent seasonal compensatory mortality occurred. Consistent with our prediction, annual survival was higher at remote sites (adult males: 0.50, 95% credible interval CrI = 0.42–0.57; adult females: 0.36, 95% CrI = 0.26–0.46; juveniles: 0.39, 95% CrI = 0.29–0.50) than at accessible sites (adult males: 0.36, 95% CrI = 0.26–0.46; adult females: 0.23, 95% CrI = 0.12–0.32; juveniles: 0.25, 95% CrI = 0.13–0.37) for all demographic groups. Concentrated harvest occurred in accessible sites during the hunting season (Aug–Mar). During the post‐breeding season (Aug–Nov), when willow ptarmigan were near their breeding sites and the hunting season was open, survival was higher for those from remote sites than for those from accessible sites when accounting for demographic group (adult male, adult female, juvenile). In contrast, during winter (Dec–Mar), when willow ptarmigan had moved away from breeding territories and were no longer segregated into remote and accessible sites, survival estimates did not differ between those from remote breeding territories and those from accessible breeding territories. This pattern of differential survival indicates an association between concentrated hunting at accessible sites and reduced survival, and it suggests an additive component of harvest mortality. In addition, the timing of these survival patterns relative to seasonal movements suggests that early season harvest (prior to seasonal movements away from breeding territories) may have a greater impact on local breeders in accessible areas than later harvest.
We examined the hypothesis that spatially and seasonally concentrated harvest decreases annual survival probabilities of willow ptarmigan (Lagopus lagopus) breeding in accessible areas. The pattern of differential survival observed indicated an association between concentrated hunting at accessible sites and reduced survival, and it suggested an additive component of harvest mortality. In addition, the timing of these survival patterns relative to seasonal movements suggests that early season harvest (prior to seasonal movements away from breeding territories) may have a greater impact on local breeders in accessible areas than later harvest.
Shrubs have expanded in Arctic ecosystems over the past century, resulting in significant changes to albedo, ecosystem function, and plant community composition. Willow and rock ptarmigan (Lagopus ...lagopus, L. muta) and moose (Alces alces) extensively browse Arctic shrubs, and may influence their architecture, growth, and reproduction. Furthermore, these herbivores may alter forage plants in such a way as to increase the quantity and accessibility of their own food source. We estimated the effect of winter browsing by ptarmigan and moose on an abundant, early-successional willow (Salix alaxensis) in northern Alaska by comparing browsed to unbrowsed branches. Ptarmigan browsed 82-89% of willows and removed 30-39% of buds, depending on study area and year. Moose browsed 17-44% of willows and browsed 39-55% of shoots. Browsing inhibited apical dominance and activated axillary and adventitious buds to produce new vegetative shoots. Ptarmigan- and moose-browsed willow branches produced twice the volume of shoot growth but significantly fewer catkins the following summer compared with unbrowsed willow branches. Shoots on browsed willows were larger and produced 40-60% more buds compared to unbrowsed shoots. This process of shoot production at basal parts of the branch is the mechanism by which willows develop a highly complex "broomed" architecture after several years of browsing. Broomed willows were shorter and more likely to be re-browsed by ptarmigan, but not moose. Ptarmigan likely benefit from the greater quantity and accessibility of buds on previously browsed willows and may increase the carrying capacity of their own habitat. Despite the observed tolerance of willows to browsing, their vertical growth and reproduction were strongly inhibited by moose and ptarmigan. Browsing by these herbivores therefore needs to be considered in future models of shrub expansion in the Arctic.
Prevalence of influenza A virus (IAV) infections in northern-breeding waterfowl has previously been reported to reach an annual peak during late summer or autumn; however, little is known about IAV ...infection dynamics in waterfowl populations persisting at high-latitude regions such as Alaska, during winter. We captured mallards (Anas platyrhynchos) throughout the non-breeding season (August-April) of 2012-2015 in Fairbanks and Anchorage, the two largest cities in Alaska, to assess patterns of IAV infection and antibody production using molecular methods and a standard serologic assay. In addition, we used virus isolation, genetic sequencing, and a virus microneutralization assay to characterize viral subtypes and to evaluate the immune response of mallards captured on multiple occasions through time. We captured 923 mallards during three successive sampling years: Fairbanks in 2012/13 and 2013/14, and Anchorage in 2014/15. Prevalence varied by age, season, and year/site with high and relatively stable estimates throughout the non-breeding season. Infected birds were detected in all locations/seasons except early-winter in Fairbanks during 2013/14. IAVs with 17 combinations of hemagglutinin (H1-5, H7-9, H11, H12) and neuraminidase (N1-6, N8, N9) subtypes were isolated. Antibodies to IAVs were detected throughout autumn and winter for all sampling locations and years, however, seroprevalence was higher among adults and varied among years. Mallards exhibited individual heterogeneity with regard to immune response, providing instances of both seroconversion and seroreversion to detected viral subtypes. The probability that an individual transitioned from one serostatus to another varied by age, with juvenile mallards having higher rates of seroconversion and seroreversion than adults. Our study provides evidence that a diversity of IAVs circulate in populations of mallards wintering at urban locations in Alaska, and we suggest waterfowl wintering at high-latitudes may play an important role in maintenance of viruses across breeding seasons.
Nest survival is one of the most important parameters in the population dynamics of grassland-nesting ducks (Anas and Aythya spp.) that breed in the Prairie Pothole Region of North America. Grassland ...habitats used by these species are increasingly threatened by habitat loss and the coincident fragmentation, which may indirectly alter nest survival through effects on predators. Although predators are the dominant cause of nest loss, they are difficult to monitor directly. Thus, indirect analyses of habitat variables are required. Many studies have attempted to address the relationship between fragmentation and nest survival; however, few studies have examined the influence of fragmentation at multiple spatial scales. Understanding how landscape characteristics at multiple spatial scales explain variation in nest survival is important, because no single correct scale is likely to exist for a diversity of landscape metrics. We examined the relationships between habitat variables and duck nest survival ($n \approx 4200 nests$) on $18 10.4-km^2$ sites selected across a gradient of landscape characteristics in the Missouri Coteau Region of North Dakota. We evaluated both a priori and exploratory competing models of nest survival that considered habitat features measured at nest sites, within nesting patches, and at multiple landscape scales. We used generalized nonlinear mixed-modeling techniques to model nest survival rates. Information-theoretic techniques were used to select among competing models. Models that included covariates measured at multiple landscape scales were better than simpler models that included only covariates measured at a single spatial scale. Landscape covariates measured at 10.4 and $41.4 km^2$ resulted in the best explanation of nest survival. Nest survival was positively related to the amount of grassland habitat, negatively related to the wetland density, and related to the amount of grassland edge in a quadratic manner, with the lowest nest survival at intermediate values of grassland edge. Future research should attempt to determine the causes of these relationships, something we were unable to do with our correlative approach. Conservation efforts focused on maintaining duck populations should seek to maintain landscapes with abundant grassland and to account for the influence of configuration using GIS analyses.
1. Model-based distance sampling is commonly used to understand spatial variation in the density of wildlife species. The standard approach assumes that individuals are distributed uniformly and ...models spatial variation in density using plot-level effects. Thinned point process (TPP) models for surveys of unmarked populations (spatial distance sampling) better leverage the spatial information underlying individual encounters, and in the presence of within-plot variation in density, may explain a larger proportion of the spatial variation in density. However, existing spatial distance sampling approaches are conditioned on the assumption that all individuals are present and available for sampling. Temporary emigration of individuals can therefore result in biased estimates of abundance. 2. We extended spatial distance sampling models to accommodate temporary emigration (TPP model). Using simulations of a thinned inhomogeneous point process, we assessed the performance of the TPP model relative to the temporary emigration distance sampling (TEDS) model, which implies a uniform distribution of individuals. In addition, we compared inferences between TPP and TEDS models using data for two passerine species in Alaska. 3. Parameter estimates from the TPP model exhibited improved coverage probability and precision relative to the TEDS model including a 26% reduction in the coefficient of variation (CV) of the population size estimate. 4. In the applied example, the TEDS model indicated weak relationships between abundance and habitat covariates, whereas the TPP model indicated strong relationships for those same effects, suggesting that spatial distance sampling models can provide considerably stronger inference in the presence of within-plot variation in density. In addition, the CV of the population size estimates for the two passerine species were 32% and 4% smaller under the TPP model. 5. Synthesis and applications. We expect our extension accommodating temporary emigration will be a critical specification for spatial distance sampling models, particularly for studies assessing changes in the distribution and abundance of highly mobile species including passerines.
Patients with a single episode of neurologic dysfunction and brain magnetic resonance imaging (MRI) scans suggestive of multiple sclerosis are at high risk for clinically definite multiple sclerosis, ...but the outcome for individual patients is unpredictable. An increased risk of progression to clinically definite multiple sclerosis in patients with serum antibodies against myelin oligodendrocyte glycoprotein (MOG) and myelin basic protein (MBP) has been reported.
We measured serum anti-MOG and anti-MBP IgG and IgM antibodies in 462 patients with a first clinical event suggestive of multiple sclerosis and at least two clinically silent lesions on brain MRI. The patients were participating in a multicenter trial of treatment with interferon beta-1b. Antibodies were assessed by Western blot analysis at baseline, and the results compared with the time and rate of progression to clinically definite multiple sclerosis or a diagnosis of multiple sclerosis as defined by an international panel (the McDonald criteria). Regular visits were scheduled for the assessment of neurologic impairment and for MRI before treatment and at months 3, 6, 9, 12, 18, and 24.
No associations were found between the presence of anti-MOG and anti-MBP IgM and IgG antibodies and progression to clinically definite multiple sclerosis or a diagnosis of multiple sclerosis according to the McDonald criteria, either in the entire cohort or in any subgroups of the study population.
Serum antibodies against MOG and MBP, as detected by Western blot analysis, are not associated with an increased risk of progression to clinically definite multiple sclerosis in patients who have had a clinically isolated syndrome suggestive of multiple sclerosis.
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