RESUMO
Inferences about the mechanisms of distributional change are often made from simple assessments of variation in the geographical positions of populations. However, direct assessments of species' responses to local habitat change may be necessary for proper understanding of the drivers of distributional dynamics. Amplified climate warming is inducing cascading impacts in boreal-tundra regions including the expansion of conifers and deciduous shrubs (shrubs). In Denali National Park (Denali), Alaska, passerine birds are exhibiting rapid upslope shifts in distribution but the relative roles of conifer and shrub (woody vegetation) expansion in driving these shifts are unknown. Without directly assessing passerine-vegetation dynamics, the assumption has been that the observed upslope shifts are indicative of shrub-adapted passerines tracking the upslope expansion of shrubs. Here, we jointly investigate the processes of conifer and shrub expansion and their relationship to changes in passerine abundance in Denali. We used a remotely sensed vegetation cover timeseries (1985-2020) to assess the topographic and edaphic correlates of conifer and shrub expansion. We then assessed the impacts of changes in shrub and conifer cover on the relative abundance of 12 passerine species (1995-2020). Shrub and conifer colonization rates were highest at intermediate elevations near treeline. However, forest- and shrub-adapted passerines differed in terms of the location in which their response was concentrated relative to treeline. The population growth rates of forest-adapted passerines exhibited stronger effects of woody vegetation expansion at sites that were initially above treeline (IAT). In contrast, the population growth rates of shrub-adapted passerines exhibited the negative effects of conifer expansion together with the positive effects of shrub expansion at initially below treeline sites. However, they showed a weak response to woody vegetation expansion at sites that were IAT. Below treeline conifer infilling appears to be pushing the elevational distributions of shrub-adapted passerines upslope rather than these species following the pull of modest shrub expansion above treeline, as previously assumed. Overall, our findings illustrate the need for explicitly accommodating heterogeneity in habitat change at small spatial scales to properly view the distributional response, particularly when habitat change is concentrated at ecotones.
Assuntos
Passeriformes , Árvores , Animais , Ecossistema , Florestas , Tundra , Mudança ClimáticaRESUMO
Climatic factors act on populations at multiple timescales leading to the separation of long-term climate and shorter-term weather effects. We used passerine counts from 1995 to 2019 in subarctic Alaska (Denali National Park, USA) to assess the impacts of the prior breeding season's weather on breeding season abundance and the impacts of climate measured through shifts in elevational distribution. Weather and climate appear to have had opposing effects on the abundance of some shrub-associated species as evidenced by a positive response to nesting phase temperature over a 1-year lag and a negative response to warming-induced shifts in shrub-dominated habitats over the long term. The latter response was indicated by declines in abundance which occurred in some part through portions of these populations shifting upslope of our fixed sampling frame. Overall, the abundance of species was related to one or more of the lagged effects of weather and the effects of weather alone drove nearly twofold variation in annual abundance in most species. The effect of nesting phase temperature was a strong positive predictor at both community and individual species levels, whereas arrival phase temperature had weak support at both levels. The effects of total precipitation during the nesting phase and snowmelt timing shared mixed support at community and species levels, but generally indicated higher abundance following seasons that were drier and had earlier snowmelt. Together, our findings of opposing effects of climatic variables at different timescales have implications for understanding the mechanisms of population and distributional change in passerines in the subarctic.
Assuntos
Mudança Climática , Passeriformes , Alaska , Animais , Estações do Ano , Temperatura , Tempo (Meteorologia)RESUMO
For migrating animals, realized migration routes and timing emerge from hundreds or thousands of movement decisions made along migration routes. Local weather conditions along migration routes continually influence these decisions, and even relatively small changes in en route weather may cumulatively result in major shifts in migration patterns. Here, we analysed satellite tracking data to score a discrete navigation decision by a large migratory bird as it navigated a high-latitude, 5000 m elevation mountain range to understand how those navigational decisions changed under different weather conditions. We showed that wind conditions in particular areas along the migration pathway drove a navigational decision to reroute a migration; conditions encountered predictably resulted in migrants routing either north or south of the mountain range. With abiotic conditions continuing to change globally, simple decisions, such as the one described here, might additively emerge into new, very different migration routes.
Assuntos
Migração Animal , Águias/fisiologia , Tempo (Meteorologia) , Alaska , Animais , Modelos Biológicos , Tecnologia de Sensoriamento Remoto/veterinária , VentoRESUMO
Vertebrate populations throughout the circumpolar north often exhibit cyclic dynamics, and predation is generally considered to be a primary driver of these cycles in a variety of herbivore species. However, weather and climate play a role in entraining cycles over broad landscapes and may alter cyclic dynamics, although the mechanism by which these processes operate is uncertain. Experimental and observational work has suggested that weather influences primary productivity over multi-year time periods, suggesting a pathway through which weather and climate may influence cyclic herbivore dynamics. Using long-term monitoring data, we investigated the relationships among multi-year weather conditions, measures of primary productivity, and the abundance of two cyclic herbivore species: snowshoe hare and northern red-backed vole. We found that precipitation (rain and snow) and growing season temperatures were strongly associated with variation in primary productivity over multi-year time horizons. In turn, fourfold variation in the amplitude of both the hare and vole cycles observed in our study area corresponded to long-term changes in primary productivity. The congruence of our results for these two species suggests a general mechanism by which weather and climate might influence cyclic herbivore population dynamics. Our findings also suggested that the association between climate warming and the disappearance of cycles might be initiated by changes in primary productivity. This work provides an explanation for observed influences of weather and climate on primary productivity and population cycles and will help our collective understanding of how future climate warming may influence these ecological phenomena in the future.
Assuntos
Lebres , Herbivoria , Animais , Clima , Dinâmica Populacional , Estações do Ano , Tempo (Meteorologia)RESUMO
The Arctic Warbler (Phylloscopus borealis) is a cryptically plumed songbird with an uncommon Nearctic-Paleotropical migratory strategy. Using light-level geolocators, we provide the first documentation of the migratory routes and wintering locations of two territorial adult male Arctic Warblers from Denali National Park and Preserve, Alaska. After accounting for position estimation uncertainties and biases, we found that both individuals departed their breeding grounds in early September, stopped over in southeastern Russia and China during autumn migration, then wintered in the Philippines and the island of Palau. Our documentation of Arctic Warbler wintering on Palau suggests that additional study is needed to document their wintering range. Our study provides hitherto unknown information on stopover and wintering locations for Arctic Warblers and indicates that this species may migrate further overwater than previously thought.
RESUMO
Unintended effects of recreational activities in protected areas are of growing concern. We used an adaptive-management framework to develop guidelines for optimally managing hiking activities to maintain desired levels of territory occupancy and reproductive success of Golden Eagles (Aquila chrysaetos) in Denali National Park (Alaska, U.S.A.). The management decision was to restrict human access (hikers) to particular nesting territories to reduce disturbance. The management objective was to minimize restrictions on hikers while maintaining reproductive performance of eagles above some specified level. We based our decision analysis on predictive models of site occupancy of eagles developed using a combination of expert opinion and data collected from 93 eagle territories over 20 years. The best predictive model showed that restricting human access to eagle territories had little effect on occupancy dynamics. However, when considering important sources of uncertainty in the models, including environmental stochasticity, imperfect detection of hares on which eagles prey, and model uncertainty, restricting access of territories to hikers improved eagle reproduction substantially. An adaptive management framework such as ours may help reduce uncertainty of the effects of hiking activities on Golden Eagles.
Assuntos
Conservação dos Recursos Naturais/métodos , Águias , Espécies em Perigo de Extinção , Recreação , Alaska , Animais , Tomada de Decisões , Modelos Teóricos , Medição de Risco , IncertezaRESUMO
Rock ptarmigan (Lagopus muta) and willow ptarmigan (L. lagopus) are Arctic birds with a circumpolar distribution but there is limited knowledge about their status and trends across their circumpolar distribution. Here, we compiled information from 90 ptarmigan study sites from 7 Arctic countries, where almost half of the sites are still monitored. Rock ptarmigan showed an overall negative trend on Iceland and Greenland, while Svalbard and Newfoundland had positive trends, and no significant trends in Alaska. For willow ptarmigan, there was a negative trend in mid-Sweden and eastern Russia, while northern Fennoscandia, North America and Newfoundland had no significant trends. Both species displayed some periods with population cycles (short 3-6 years and long 9-12 years), but cyclicity changed through time for both species. We propose that simple, cost-efficient systematic surveys that capture the main feature of ptarmigan population dynamics can form the basis for citizen science efforts in order to fill knowledge gaps for the many regions that lack systematic ptarmigan monitoring programs.
Assuntos
Galliformes , Alaska , Animais , Regiões Árticas , Groenlândia , América do Norte , Dinâmica Populacional , Federação Russa , Svalbard , SuéciaRESUMO
The peregrine falcon (Falco peregrinus) and the gyrfalcon (Falco rusticolus) are top avian predators of Arctic ecosystems. Although existing monitoring efforts are well established for both species, collaboration of activities among Arctic scientists actively involved in research of large falcons in the Nearctic and Palearctic has been poorly coordinated. Here we provide the first overview of Arctic falcon monitoring sites, present trends for long-term occupancy and productivity, and summarize information describing abundance, distribution, phenology, and health of the two species. We summarize data for 24 falcon monitoring sites across the Arctic, and identify gaps in coverage for eastern Russia, the Arctic Archipelago of Canada, and East Greenland. Our results indicate that peregrine falcon and gyrfalcon populations are generally stable, and assuming that these patterns hold beyond the temporal and spatial extents of the monitoring sites, it is reasonable to suggest that breeding populations at broader scales are similarly stable. We have highlighted several challenges that preclude direct comparisons of Focal Ecosystem Components (FEC) attributes among monitoring sites, and we acknowledge that methodological problems cannot be corrected retrospectively, but could be accounted for in future monitoring. Despite these drawbacks, ample opportunity exists to establish a coordinated monitoring program for Arctic-nesting raptor species that supports CBMP goals.
Assuntos
Ecossistema , Falconiformes , Animais , Canadá , Groenlândia , Estudos Retrospectivos , Federação RussaRESUMO
While collating contributions and comments from 36 researchers, the coordinating authors accidentally omitted Dr. Suzanne Carrière from the list of contributing co-authors. Dr. Carrière's data are described in Tables 1 and 3, Figure 2 and several places in the narrative.The new author list is thus updated in this article.
RESUMO
Perturbation analysis is a powerful tool to study population and community dynamics. This article describes expressions for sensitivity metrics reflecting changes in equilibrium occupancy resulting from small changes in the vital rates of patch occupancy dynamics (i.e., probabilities of local patch colonization and extinction). We illustrate our approach with a case study of occupancy dynamics of Golden Eagle (Aquila chrysaetos) nesting territories. Examination of the hypothesis of system equilibrium suggests that the system satisfies equilibrium conditions. Estimates of vital rates obtained using patch occupancy models are used to estimate equilibrium patch occupancy of eagles. We then compute estimates of sensitivity metrics and discuss their implications for eagle population ecology and management. Finally, we discuss the intuition underlying our sensitivity metrics and then provide examples of ecological questions that can be addressed using perturbation analyses. For instance, the sensitivity metrics lead to predictions about the relative importance of local colonization and local extinction probabilities in influencing equilibrium occupancy for rare and common species.
Assuntos
Águias/fisiologia , Ecossistema , Modelos Biológicos , Dinâmica Populacional , Animais , Modelos Estatísticos , Sensibilidade e EspecificidadeRESUMO
One of the central goals of the field of population ecology is to identify the drivers of population dynamics, particularly in the context of predator-prey relationships. Understanding the relative role of top-down versus bottom-up drivers is of particular interest in understanding ecosystem dynamics. Our goal was to explore predator-prey relationships in a boreal ecosystem in interior Alaska through the use of multispecies long-term monitoring data. We used 29 years of field data and a dynamic multistate site occupancy modeling approach to explore the trophic relationships between an apex predator, the golden eagle, and cyclic populations of the two primary prey species available to eagles early in the breeding season, snowshoe hare and willow ptarmigan. We found that golden eagle reproductive success was reliant on prey numbers, but also responded prior to changes in the phase of the snowshoe hare population cycle and failed to respond to variation in hare cycle amplitude. There was no lagged response to ptarmigan populations, and ptarmigan populations recovered quickly from the low phase. Together, these results suggested that eagle reproduction is largely driven by bottom-up processes, with little evidence of top-down control of either ptarmigan or hare populations. Although the relationship between golden eagle reproductive success and prey abundance had been previously established, here we established prey populations are likely driving eagle dynamics through bottom-up processes. The key to this insight was our focus on golden eagle reproductive parameters rather than overall abundance. Although our inference is limited to the golden eagle-hare-ptarmigan relationships we studied, our results suggest caution in interpreting predator-prey abundance patterns among other species as strong evidence for top-down control.