• Assessing effects of climate change on access to ecosystem services in rural Alaska

      Cold, Helen S.; Brinkman, Todd J.; Hollingsworth, Teresa N.; Brown, Caroline L.; Verbyla, David L. (2018-12)
      Across the planet, climate change is altering the way human societies interact with the environment. Amplified climate change at high latitudes is significantly altering the structure and function of ecosystems, creating challenges and necessitating adaptation by societies in the region that depend on local ecosystem services for their livelihoods. Rural communities in Interior Alaska rely on plants and animals for food, clothing, fuel and shelter. Previous research suggests that climate-induced changes in environmental conditions are challenging the abilities of rural residents to travel across the land and access local resources, but detailed information on the nature and effect of specific conditions is lacking. My objectives were to identify climate-related environmental conditions affecting subsistence access, and then estimate travel and access vulnerability to those environmental conditions. I collaborated with nine Interior Alaskan communities within the Yukon River basin and provided local residents with camera-equipped GPS units to document environmental conditions directly affecting access for 12 consecutive months. I also conducted comprehensive interviews with research participants to incorporate the effects of environmental conditions not documented with GPS units. Among the nine communities collaborating on this research, 18 harvesters documented 479 individual observations of environmental conditions affecting their travel with GPS units. Environmental conditions were categorized into seven condition types. I then ranked categories of conditions using a vulnerability index that incorporated both likelihood (number of times a condition was documented) and sensitivity (magnitude of the effect from the condition) information derived from observations and interviews. Changes in ice conditions, erosion, vegetative community composition and water levels had the greatest overall effect on travel and access to subsistence resources. Environmental conditions that impeded travel corridors, including waterways and areas with easily traversable vegetation (such as grass/sedge meadows and alpine tundra), more strongly influenced communities off the road network than those connected by roads. Combining local ecological knowledge and scientific analysis presents a broad understanding of the effects of climate change on access to subsistence resources, and provides information that collaborating communities can use to optimize adaptation and self-reliance.
    • Ecological effects of invasive European bird cherry (Prunus padus) on salmonid food webs in Anchorage, Alaska streams

      Roon, David A.; Wipfli, Mark; Prakash, Anupma; Wurtz, Tricia (2011-08)
      Invasive species are a concern worldwide as they can displace native species, reduce biodiversity, and disrupt ecological processes. European bird cherry (Prunus padus) (EBC) is an invasive ornamental tree that is rapidly spreading and possibly displacing native trees along streams in parts of urban Alaska. The objectives of this study were to: 1) map the current distribution of EBC along two Anchorage streams, Campbell and Chester creeks, and 2) determine the effects of EBC on selected ecological processes linked to stream salmon food webs. Data from the 2009 and 2010 field seasons showed: EBC was widely distributed along Campbell and Chester creeks; EBC leaf litter in streams broke down rapidly and supported similar shredder communities to native tree species; and EBC foliage supported significantly less terrestrial invertebrate biomass relative to native deciduous tree species, and contributed significantly less terrestrial invertebrate biomass to streams compared to mixed native vegetation, but riparian EBC did not appear to affect the amount of terrestrial invertebrate prey ingested by juvenile coho salmon (Oncorhynchus kisutch). Although ecological processes did not seem to be dramatically affected by EBC presence, lowered prey abundance as measured in this study may have long-term consequences for stream-rearing fishes as EBC continues to spread over time.
    • Feeding ecology of scaup ducklings across a heterogeneous boreal wetland landscape

      DuBour, Adam J.; Lindberg, Mark; Gurney, Kirsty; Hundertmark, Kris (2019-08)
      Understanding how patterns of food resources influence the behavior and fitness of free-living animals is critical in predicting how changes to such resources might influence populations. The boreal region of North America is relatively undeveloped and contains abundant freshwater lakes and wetlands. These largely pristine and stable habitats harbor high densities of aquatic invertebrates, which are a critical food source for the numerous waterbird species that breed in the boreal. Invertebrates are of particular importance for the optimal growth and survival of waterbird chicks. However, observations of long-term change to boreal aquatic habitats and their invertebrate populations associated with a warming climate has been implicated in the declines of some boreal breeding waterbirds, such as the lesser scaup (Aythya affinis). Lesser scaup are known to feed extensively on amphipods, a freshwater crustacean; however, ducklings have been shown to have a diverse diet. Our goal was to use the naturally occurring heterogeneity of aquatic invertebrates across boreal lakes within the Yukon Flats National Wildlife Refuge in interior Alaska to better understand how changes in invertebrate prey resources might affect diet selection and growth in lesser scaup ducklings. First, we used a stable isotope approach to quantify the variation in the trophic niche within our population of ducklings. We found that as a population, lesser scaup ducklings consume a variety of aquatic insects, crustaceans and mollusks, and that variation in the population diet is largely attributable to variation in diet between birds from different lakes with different invertebrate communities. Second, we used the same habitat heterogeneity to examine how gradients of invertebrate abundance relate to the growth of ducklings. We observed that lesser scaup ducklings experienced reduced growth rates in lakes that had little to no amphipods. Taken together, these results suggest that while lesser scaup ducklings are a flexible consumer that can adapt to changes in invertebrate populations, ducklings may face negative fitness repercussions when consuming prey other than amphipods.
    • Foliage and winter woody browse quality of an important Salix browse species: effects of presence of alder-derived nitrogen and winter browsing by Alaskan moose (Alces alces gigas)

      Burrows, Justin; Kielland, Knut; Wagner, Diane; Ruess, Roger (2019-12)
      In this study, I examined the relationship between soil nitrogen and winter browsing by moose on the physical and chemical characteristics of Salix alaxensis; specifically stem production, leaf nutritional quality, and stem nutritional quality of tissues produced the following growing season. I measured stem biomass production the 2013 growing season and offtake during the 2013-2014 winter browsing season at 16 sites on the Tanana River floodplain near Fairbanks, Alaska. I revisited the sites the following summer and autumn to assess regrowth and to collect soil, foliage, and stem samples. Browsing intensity and total soil nitrogen were similar in sites with and without alder, a nitrogen-fixing shrub. Soil nitrogen and browsing intensity were not consistently related to changes in stem or leaf quality, although there were significant relationships in some subsets. Soil nitrogen and browsing intensity also did not have consistent relationships with stem regrowth the following growing season. These results indicate that S. alaxensis growing in this system are able to recover from a naturally broad range of browsing utilization, including very high levels of offtake, and continue to produce nutritious leaves and stems.
    • Investigating ancient bison migration in Alaska: a bottom up approach using isotopes

      Funck, Juliette Marie; Wooller, Matthew; Druckenmiller, Patrick; Hundertmark, Kris; Ruether, Joshua (2020-05)
      Once abundant in the Arctic, bison (Bison bison) declined almost to extinction in the North but have subsequently been reintroduced into Alaska. The predecessors of these modern bison were the ancient steppe bison (Bison priscus), which were abundant throughout the Northern Hemisphere before their extinction during the Holocene. This thesis investigates the ecology and landscape-use of both the present-day wood bison (Bison bison athabascae) and the ancient steppe bison in Alaska using stable isotopes, among other methods. The stable carbon and nitrogen isotope compositions of animal tissues are traditionally used to investigate diet. However, this thesis uses the isotope composition of tail hairs from present day wood bison as a proxy for their nutritional stress. Nutritional stress of some wood bison appears to be influenced not only by food shortage during hard seasons, but also due to long-distance mobility. This insight provides a key to understanding the challenges of reintroduction of the species into Alaska today, and can also be applied to understand the nutritional stress and cost of dispersal by ancient animals. Whereas the mobility of present-day bison can be tracked using sophisticated satellite tracking technologies, studies of the paleo-mobility of ancient bison rely on isotopic markers such as strontium and oxygen isotope ratios preserved in their teeth. To aid this approach using isotopic geolocation, this thesis creates a map of bioavailable strontium modeled and based on strontium isotope composition of present-day rodent teeth from across Alaska. It then compares this map, together with an existing oxygen isotope map of precipitation in Alaska, with the strontium and oxygen isotopes preserved in a suite of ancient bison from Northern Alaska. This comparison brings to light some of the major habitation regions used by Bison on the North Slope of Alaska over the last ~50,000 years. Finally, these findings subsequently contribute to a detailed paleoecological investigation of a mostly articulated and complete ancient steppe bison found on the North Slope of Alaska. This final study reveals the life-history of an individual bison that dispersed from the coastal plain to the foothills of the Brooks Range early in his life, and shows that the trip was nutritionally costly. This information is combined with a suite of other paleoecological methods to provide a vivid life history of this ancient bison. We introduce new methodologies for studying these ancient animals that seek to bridge the gap between how we study present-day and the past.
    • Movement and migration ecology of Alaskan golden eagles

      Eisaguirre, Joseph Michael; Breed, Greg; Booms, Travis; Doak, Pat; Kielland, Knut; McIntyre, Carol (2020-05)
      Golden eagles Aquila chrysaetos are distributed across the Holarctic; however, in Alaska and other northern areas, many are long-distance migrants. Being soaring birds, golden eagles can use weather and features of the energy landscape to offset the energetic costs of movement and migration. In this dissertation, I investigate how dynamic energy landscapes, in addition to other habitat and anthropogenic features, affect the movement and migration ecology of Alaskan golden eagles; in most cases I did such by developing and applying new, biologically-appropriate statistical methods. First, I identified a single, discrete navigation decision that each eagle made during migration and determined which weather variables are primary factors in driving that decision. I found that wind was the primary correlate to the decision, consistent with eagles likely avoiding poor migration conditions and choosing routes based on favorable wind conditions. Second, I investigated how different forms of flight subsidies, which were orographic uplift, thermal uplift, and wind support, drove behavioral budgets and migratory pacing of eagles. I found a consistent daily rhythm in eagle behavior and migratory pace, seemingly driven by daily development of thermal uplift, with extended periods of slower-paced movements, consistent with periods of opportunistic foraging. Third, I investigated the effects of anthropogenic linear features, such as roads and railroads, on eagle movement during migration. I found that eagles selected for roads during spring migration and were more likely to be near roads when making slower-paced movements, which would be most frequent during times when limited thermal uplift is available. Lastly, I compared how floaters (breeding-age, non-territorial individuals) and territorial eagles used space and selected for resources, specifically interested in how their movements and space use might overlap. I found that floater space use was much more expansive, yet they only selected for habitats and resources slightly differently than territorial eagles. I also found their home ranges overlap substantially, suggesting that floaters play a key role in the population ecology of migratory golden eagles in Alaska.
    • Population ecology of willow ptarmigan (Lagopus lagopus) in the presence of spatially concentrated harvest

      Frye, Graham G.; Lindberg, Mark; Brainerd, Scott; Kielland, Knut; Schmidt, Joshua (2020-05)
      Understanding the potential effects of harvest on wildlife populations is fundamental to both theoretical wildlife science and applied wildlife management. The effects of harvest on wildlife populations vary dramatically and depend on the timing and magnitude of harvest, as well as population-specific states and vital rates. Demographic compensation plays a key role in models of wildlife population dynamics and in developing harvest strategies. However, the degree and form of compensation in a given population depends on its particular ecological and life history characteristics, resulting in the need for population-specific assessments of responses to harvest. Ptarmigan (Lagopus spp.) are ecologically important species and are culturally valued for subsistence and recreational hunting throughout the Holarctic. In Alaska, willow ptarmigan (L. lagopus) are among the most commonly harvested small game species, but the population-level effects of harvest are not well understood. Investigating the population level effects of harvest on these populations would aid harvest management and increase general understanding of the ecology of the species. To this end, I studied the population ecology of willow ptarmigan in a region of Alaska with spatially concentrated harvest along access corridors. I investigated: (1) the effect of harvest, season, and demographic group on survival, (2) the effect of harvest on breeding densities, (3) dispersal and seasonal movements patterns in relation to harvest, and (4) temporal and observer effects on ptarmigan survey efforts. I found that survival rates and breeding densities of willow ptarmigan in heavily hunted areas were substantially lower than those in remote sites without hunting. We did not observe seasonal compensatory mortality and the potential for permanent immigration (i.e., breeding/natal dispersal) to compensate for harvest appeared limited. However, seasonal movements away from breeding territories appeared to distribute the effects of harvest more evenly among ptarmigan from accessible and remote areas during winter and early spring. This suggests that the timing of hunting seasons may play a critical role in determining effects on ptarmigan densities in accessible breeding areas, with early autumn (prior to initiation of seasonal movements) harvest likely having the greatest impact. In addition, when examining ptarmigan survey methodology, I found substantial temporal heterogeneity in the availability of ptarmigan for detection during surveys, as well as variation in observer-specific detection rates. This underscores the importance of investigators considering the role of imperfect and heterogeneous detection when designing ptarmigan monitoring strategies to avoid inaccurate conclusions about abundance and trends.
    • The response of plant community structure and productivity to changes in hydrology in Alaskan boreal peatlands

      Churchill, Amber C.; McGuire, A. David; Nettleton-Hollingsworth, Teresa; Turetsky, Merritt (2011-12)
      Northern peatlands have been a long-term sink for atmospheric CO₂, and have had a net cooling effect on global climate for the last 8,000 to 11,000 years. Across Alaska, peatlands face increased effects of climate change through hydrologic disturbance, both drying and flooding, and these conditions alter the ability of peatlands to accumulate carbon. Here, I examined the influence of changing hydrology in a moderate rich fen and a bog located in the discontinuous permafrost zone of interior Alaska. In both sites, I quantified how changing hydrology affected vegetation composition and ecosystem carbon uptake. At the fen, drying via a lowered water table treatment caused larger changes in vegetation composition and primary productivity than flooding via a raised water table treatment. In the bog, an area of recent permafrost thaw (collapse scar) had increased rates of understory net primary production and gross primary production, relative to an adjacent but older collapse scar and the surrounding permafrost plateau. Together, results from these studies highlight possible community responses to projected change in water availability, whether through drying or flooding, and demonstrate initial mechanisms for community responses altering ecosystem processes.