Recent Submissions

  • Terrestrial invertebrate prey for juvenile chinook salmon: abundance and environmental controls in an Interior Alaska river

    Gutierrez, Laura; Wipfli, Mark S.; Blanchard, Amy L.; Rosenberger, Amanda E. (2011-12)
    Terrestrial prey subsidies can be a key food source for stream fish, but their importance and environmental controls on their abundance have not been widely documented in high latitude ecosystems. This study investigated terrestrial invertebrate prey availability and predation by age-0+ juvenile chinook salmon (Oncorhynchus tshawytscha), overlap between terrestrial infall and drift to diet, and the relationship between diet to stream temperature and discharge in the Chena River, Interior Alaska. Terrestrial infall, drift, and juvenile chinook diet varied widely through the summers (May-September) of 2008 and 2009. Drift was comprised of 33% terrestrial and 67% aquatic invertebrate mass, while juvenile chinook diet contained 19% terrestrial, 80% aquatic, and 1% unidentifiable invertebrate mass. The proportion of terrestrial invertebrate mass consumed increased through summer and, at times, made up to 39% of total diet. Low similarity of invertebrates in diet and infall, and diet and drift suggested that fish were, in part, prey-selective, selecting hymenopterans and chironomid midges (Diptera). In both years, prey mass consumed and discharge varied inversely, but no correlation was found between proportion of terrestrial invertebrates consumed and discharge. However, the two sampling dates with the highest proportion of terrestrial invertebrates consumed occurred shortly after a 60-year flood, indicating that terrestrial invertebrates may be important during rain and associated high water. This study found that, although terrestrial infall and drift are highly variable, terrestrial invertebrates are an important prey resource for rearing chinook salmon in this high latitude riverine system, especially later in the summer.
  • Novel fungal taxa in an Alaskan boreal forest: phylogenetic affinities, ecologies, and ribosomal RNA secondary structures

    Glass, Daniel; Taylor, D. Lee; Olson, Link E.; Takebayashi, Naoki; Duffy, Lawrence (2011-12)
    Phylogenetic analyses suggest that a novel DNA sequence (NS1) found in a boreal forest soil-clone library belongs to the fungal kingdom but does not fall unambiguously within any known class. In order to determine if NS1 codes for an authentic ribosomal RNA (rRNA) gene-copy, I modeled ribosomal RNA secondary structure for four gene regions. Such analyses have never been used on environmental ribosomal sequences before. It appears that NS1 does code for an authentic gene-copy and is not a biological or lab artifact. I also elucidated the habitat preferences, horizon preferences, and fine-scale spatial structure of NS1 using molecular methods. I determined that NS1 was associated with spruce and was found in both the organic and mineral soil horizons. It appears to have a clumped distribution on the scale of a few meters and its spatial distribution shows little inter-annual variability. Together these findings suggest that NS1 does represent an authentic gene-copy and also shed light on the ecology of this putative taxon. I hope future efforts will expand our understanding of both its identity and function.
  • Reproductive ecology and morphometric subspecies comparisons of Dunlin (Calidris alpina), an arctic shorebird

    Gates, Heather River; Powell, Abby N.; Hunter, Christine M.; Lanctot, Richard B. (2011-12)
    The Arctic region provides globally important breeding and migratory habitat for abundant wildlife populations including migratory shorebirds. Due to their remote breeding locations, basic information on breeding ecology, annual productivity, and factors that regulate their populations are poorly studied. Wildlife biologists managing migratory bird populations require detailed information on avian breeding biology, in addition to information on migration ecology including connectivity of migratory stopover and wintering locations. To address information gaps in fecundity, I conducted an experimental study investigating the renesting ecology of Dunlin (Calidris alpina arcticola) by removing clutches at two stages of incubation and by following adults marked with radio transmitters to their replacement clutch. In contrast to predictions for arctic-breeding species, Dunlin had high (82-95%) rates of clutch replacement during early incubation and moderate (35-50%) rates during late incubation. Female body condition and date of clutch loss were important variables explaining propensity for females to replace a clutch; larger females that lost their nest early in the season were more likely to renest than smaller females who lost their nest later in the season. To delineate Dunlin subspecies in areas where they overlap, I used morphological and molecular approaches to determine sex and subspecies of five subspecies of Dunlin breeding in Alaska and eastern Russia. This analysis yielded discriminant function models to correctly classify unknown individuals to sex (79-98%) and subspecies (7385%) via morphometric measures. Correct classification of mixed assemblages of subspecies improved when sex, determined though molecular techniques, was known. The equations I derived using discriminant function models can be used to identify the sex and subspecies of unknown Dunlin individuals for studies investigating breeding and migration ecology.
  • 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.
  • Body condition and reproductive strategies of female lesser scaup in the boreal forest of Alaska

    DeGroot, Kristin A.; Lindberg, Mark; Barboza, Perry; Schmutz, Joel (2011-05)
    In many waterfowl species, body condition of breeding females can contribute to reproductive success by influencing factors such as egg size, clutch size and ability to incubate eggs. In turn, changes in female condition at the population level could affect population growth rates. Large-scale declines in populations of Lesser Scaup (Aythya affinis) raised concerns that poor female body condition was contributing to declines by reducing reproductive output. However, little was known about changes in body condition over time and about the contribution that stored body reserves make to egg production, especially in boreal forest regions where most scaup breed. My objectives were: 1) examine temporal changes in body condition of pre-breeding female lesser scaup on the Yukon Flats National Wildlife Refuge, Alaska and the relationship between body condition and breeding status; 2) examine the role of body reserves (protein and lipid) in egg production using stable isotope techniques. I found no evidence for a decline in female body condition as compared to historic measures. However, females that had entered rapid follicle growth (the early stages of egg production) were significantly fatter than birds that were not currently producing eggs. In addition, I found that female lesser scaup use both body reserves and dietary nutrients for production of egg yolk.
  • 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.
  • Phylogeography and population genetics of a Beringian endemic: Dallia (Esociformes: Teleostei)

    Campbell, Matthew A.; López, J. Andrés; Takebayashi, Naoki; Olson, Matthew (2011-08)
    In this thesis I examine the population genetics of an endemic Beringian freshwater fish genus, Dallia (blackfish). The current distribution of blackfish was heavily influenced by paleoclimatic instability during the Pleistocene. Beringian paleoclimatic changes during the Pleistocene included the fluctuating growth and decline of glaciers and an overall decrease in temperature and increased aridity in areas not adjacent to the Bering Sea. Pleistocene glacial advances resulted in the cyclical emergence of the Bering land bridge. The effects of paleoclimatic instability on blackfish distribution and abundance can be inferred through the distribution of genetic variation across the Beringian landscape. I address three basic questions: 1: Are separate populations of blackfish taxonomically distinct entities? I found that while there is clear genetic structuring and isolation, there is insufficient information to make a strong statement in this regard. 2: Did blackfish survive Pleistocene glaciations within multiple Beringian refugia? My results indicate that blackfish persisted in at least four broad geographic areas. 3: How did the Bering land bridge influence intercontinental aquatic interchange? My evidence points to close genetic relationships and potentially high exchange of blackfish across the Bering land bridge, which supports the Bering land bridge as conduit for freshwater aquatic migration.
  • Arctic fox winter movement and diet in relation to industrial development on Alaska's North Slope

    Lehner, Neil S.; Person, Brian; Kielland, Knut; O'Brien, Diane; Hunter, Christine (2012-12)
    I examined winter movement and diet of Arctic foxes (Vulpes lagopus) in the Prudhoe Bay oilfields and an adjacent undeveloped area (National Petroleum Reserve-Alaska (NPR-A)). Movement metrics were compared between these areas using data from satellite collars. Daily travel rate was approximately 5 times greater in the undeveloped area than in Prudhoe Bay. Four adult foxes collared in NPR-A used the sea ice for extensive time periods. One of these foxes traveled 338 km in three days while another traveled to Banks Island (Northwest Territories, Canada), over 1050 km from its capture location. Prudhoe Bay foxes did not make these long distance movements and remained near their summer capture location throughout winter. I used stable isotope analysis and a mixing model (SIAR) to estimate the contribution of marine, terrestrial, and anthropogenic foods to fox diet. Based on muscle tissue, the average contribution of anthropogenic foods to Prudhoe Bay fox diet was more that 50%. Marine foods were utilized in NPR-A, but not in Prudhoe Bay. Results demonstrate that anthropogenic foods are heavily utilized by foxes that overwinter in the oilfields and this food source is likely responsible for reduced winter movements of Prudhoe Bay foxes. Therefore, industrial development strongly affects winter movement and diet of foxes.
  • Controls on microbial processing of dissolved organic matter in boreal forest streams

    Schmidt, Marie; Jones, Jay; Harms, Tamara; Guerard, Jennifer (2020-05)
    In the boreal forest, permafrost thaw is resulting in changes in vegetation and deepening of watershed flowpaths. Caribou-Poker Creeks Research Watershed contains sub-catchments underlain with varying permafrost extents (4-53% cover), providing the opportunity to study how permafrost extent affects water chemistry and nutrient cycling. I measured nitrogen (N), phosphorous (P), and carbon (C) processing ectoenzyme activity in the water column and sediment of headwater streams, and related ectoenzyme activity to nutrient and dissolved organic carbon (DOC) concentration. Additionally, I used nutrient diffusing substrata (NDS) to grow biofilms with enhanced inorganic N and P and labile C alone and in combination and measured ectoenzyme activity and respiration of biofilms in response to resource amendments. High P-processing enzyme activity across streams of the CPCRW indicated microbial P limitation. Respiration and organic matter processing enzymes of biofilms grown on NDS increased with labile C or labile C in combination with nutrient additions, implying that labile C limited or co-limited rates of DOM processing. Our results suggest that as climate warming and subsequent permafrost thaw alters terrestrial inputs of dissolved organic matter (DOM) and inorganic nutrients into streams, changes in inorganic P and labile C availability will control microbial processing of DOM.
  • Science, perception and scale: an interdisciplinary analysis of environmental change and community adaptive capaciy

    Grunblatt, Jesse E.; Wipfli, Mark; Adams, Barbara; Carothers, Courtney; Monahan, John (2020-05)
    The discrepancy between science-based assessments of climate change and public acknowledgement of climate change has been extensively documented at a national level. The relationship of science-based assessments and public awareness of environmental change at the local community level is less studied. An understanding of how science-based information informs local perception is important to ensure that science communication effectively supports community decision making. This dissertation explores the gap between science-based assessments and local perception of environmental change within a framework of adaptive capacity. The research is divided into three interrelated studies that provide: 1) an assessment of community perception of local environmental change, 2) a local study that illustrates science-based assessment and reporting, and 3) an evaluation of the role news media plays in communicating science to the public. The first study implemented a survey of residents on Alaska's Kenai Peninsula to evaluate individual perception of environmental change as well as attitudes regarding climate change and natural resource management. Differences in perception of local environmental change were identified among respondents as well as shared perceptions. The use of property regulation to protect the Kenai River was identified as a divisive issue; however, there was a shared concern regarding the condition of local salmon populations. A second science-based ecological study was developed that examined those issues and linked conservation of riparian vegetation to juvenile salmon rearing habitat. This study examined the diet of stream-rearing juvenile Coho Salmon (Oncorhynchus kisutch) and determined that the proportion of invertebrates which enter the stream from riparian habitats varied based on vegetation type for three streams in the Kenai watershed. The third study investigated how news media play a role in the interpretation of technical, science-based reporting for the public. It demonstrated that local news media provide a unique opportunity to promote communication of science-based information to their audiences by providing content that is familiar and relevant, offering a variety of topical framings, developing authoritative or trusted voices, and providing frequent exposure to content.
  • 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.
  • 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.
  • Growth of juvenile chinook salmon (Oncorhynchus tshawytscha) as an indicator of density-dependence in the Chena River

    Perry, Megan T. (2012-08)
    In management of Pacific salmon, it is often assumed that density-dependent factors, mediated by the physical environment during freshwater residency, regulate population size prior to smolting and outmigration. However, in years following low escapement, temperature may be setting the upper limit on growth of juvenile chinook salmon Oncorhynchus tshawytscha during the summer rearing period. Given the importance of juvenile salmon survival for the eventual adult population size, we require a greater understanding of how density-dependent and independent factors affect juvenile demography through time. In this study we tested the hypotheses that (1) juvenile chinook salmon in the Chena River are food limited, and (2) that freshwater growth of juvenile chinook salmon is positively related with marine survival. We tested the first hypotheses using an in-situ supplemental feeding experiment, and the second hypothesis by conducting a retrospective analysis on juvenile growth estimated using a bioenergetics model related to return per spawner estimates from a stock-recruit analysis. We did not find evidence of food limitation, nor evidence that marine survival is correlated with freshwater growth. However, we did find some evidence suggesting that growth during the freshwater rearing period may be limited by food availability following years when adult escapement is high.
  • Foods and foraging ecology of oldsquaws (Clangula hyemalis L.) on the arctic coastal plain of Alaska

    Taylor, Eric John (1986-09)
    The study was conducted from June to September during 1979 and 1980 in the the West Long Lake area of the National Petroleum Reserve-Alaska. Additional oldsquaws were collected in the inland wetlands near the northwest boundary of the reserve at Ice Cape. West Long Lake and the adjacent Goose Lake are located 15 miles south of the Beaufort Sea and immediately west of Teshekpuk Lake.
  • Resource limitation of autotrophs and heterotrophs in boreal forest headwater streams

    Weaver, Sophie Alden; Jones, Jeremy B.; Leigh, Mary Beth; Ruess, Roger W. (2019-12)
    In stream biofilms, autotrophs and heterotrophs are responsible for the majority of in stream nutrient transformations. In boreal forest catchments, discontinuous permafrost can lead to variation in nutrient and energy resources, which can control competition for nutrients between autotrophs and heterotrophs within these biofilms. I was interested in determining what resources control nutrient utilization by autotrophs and heterotrophs in headwater streams in the boreal forest of interior Alaska. I hypothesized that the outcome of competition between autotrophs and heterotrophs for inorganic nutrients would be dependent on the availability of (i) organic carbon, (ii) light, or (iii) inorganic nutrients. To measure resource limitation and competition at both patch and reach scales, I deployed nutrient diffusing substrata and conducted nutrient uptake experiments in streams along a permafrost gradient at the Caribou-Poker Creeks Research Watershed in interior Alaska. At the patch scale, autotrophs were light and nutrient limited, whereas heterotrophs were carbon and nutrient limited, and at the reach scale, light had the largest influence on nutrient uptake. Heterotrophs exhibited a larger response to nutrient enrichment when stream ambient carbon stocks were more bioavailable. Autotrophic biomass and productivity was suppressed when labile carbon was available to heterotrophs, suggesting that heterotrophs outcompete autotrophs for nutrients when a labile carbon source is introduced. The positive responses to nutrient and carbon additions suggest that the hypothesized increased nutrient and carbon exports into fluvial networks with permafrost degradation will impact biofilm structure and function, with the potential to influence nutrient export and stream ecosystem function downstream.
  • Host-parasite ecophysiology of overwintering

    Larson, Don J.; Barnes, Brian; O'Hara, Todd; Sikes, Derek; Wipfli, Mark (2019-12)
    To survive extreme winters, parasites must overwinter either in a host, as free-living larvae, or be reintroduced yearly through migratory hosts. This thesis examines interrelations between host parasite overwintering physiology and behavior in Alaska between the trematode Ribeiroia ondatrae and their host, wood frogs (Lithobates sylvaticus). The first chapter examines overwintering physiology and behavior of wood frogs in the field. The second chapter creates a laboratory method for determining physiological responses of wood frogs to environmental transitions from summer to fall. The third chapter examines if and how R. ondatrae survive within a frozen wood frog. Free-living wood frogs investigated over two winters in Fairbanks, AK remained frozen for up to 7 months and survived temperatures as low as -18°C, values much more extreme than those previously reported (Chapter 1). Alaskan wood frogs also synthesized and released approximately one order of magnitude greater concentrations of cryoprotectant (glucose) in multiple tissues than levels previously reported. Wood frogs in the field did not experience the same slow and continuous cooling that researchers routinely subject frogs to under experimental conditions. Instead they cooled at rates of up to -1.5°C h⁻¹ for short periods in a diurnal freeze-thaw pattern repeated over one to three weeks until remaining frozen for the rest of winter. Since wood frogs only produce glucose at the initiation of freezing, I hypothesized that freeze-thaw cycling within hibernacula allowed for incremental increases of glucose resulting in higher concentrations in field wood frogs than found in laboratory frozen wood frogs. I compared patterns of diurnal freeze-thaw cycling with the standard laboratory freezing protocols for wood frogs. Wood frogs that experienced multiple freeze-thaw events responded with significant increases in glucose concentration in liver, leg, and heart tissues at each freezing with no significant losses in glucose with each following thaw period (Chapter 2). This incremental increase in glucose within wood frogs may also assist in parasite survival. Trematode metacercariae may be absorbing host glucose and using this cryoprotectant to enhance their survival (Chapter 3). This result provides evidence that host physiology in winter may both hinder (through freezing) and facilitate (through cryoprotectant production) parasite survival.
  • Validating a GPS collar-based method to estimate parturition events and calving locations for two barren-ground caribou herds

    Hepler, Joelle D.; Griffith, Brad; Falke, Jeff; Roach, Jen (2019-12)
    In remote landscapes, it is difficult and expensive to document animal behaviors such as location and timing of parturition. When aerial surveys cannot be conducted as a result of weather, personnel or fiscal constraints, analyses of GPS collar movement data may provide an alternate way to estimate parturition rates and calving ground locations. I validated two methods (population-based method and individual-based method), developed to detect calving events of sedentary woodland caribou, on multiple years of data for two different migratory barren-ground caribou herds in Alaska, the Porcupine and Fortymile herds. I compared model estimates of population parturition rates, individual calving events, calving locations and calving dates to estimates from aerial survey data for both herds. For the Porcupine herd we also compared model estimates of annual calving ground sizes and locations of concentrated calving area centroids to those found with aerial survey. More years of data would be required for additional statistical power but for both the Porcupine and Fortymile herds, we found no significant difference between the population-based and individual-based method in: 1) individual classification rate accuracy (0.85 vs. 0.88, respectively; t = -7, P = 0.09, df = 1 and 0.85 vs. 0.83, respectively; t = 0.46, P = 0.69, df = 2) or 2) annual average distance from aerial survey calving locations (8.9 vs. 7.8 km, respectively; t = 0.16, P = 0.90, and 5.2 vs. 3.7 km, respectively; t = 1.03, P = 0.20). Median date of calving was estimated within 0-3 days of that estimated by aerial survey for both methods. Population parturition rate estimates from aerial survey, the population-based and individual-based methods were not significantly different for the PCH or FCH (0.91, 0.88 and 0.95, respectively; F = 0.67, P = 0.60, df = 2, and 0.83, 0.83 and 0.96, respectively; F = 3.85, P = 0.12, df = 2). Ultimately, more years of data would be required to support or reject the lack of significant differences between methods that we observed.
  • 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.
  • Plant succession in the Arctic Brooks Range: floristic patterns from alpine to foothills, along a glacial chronosequence and elevation gradient

    Kasanke, Shawnee A.; Walker, Donald A.; Chapin, F. Stuart III; Mann, Daniel H. (2019-08)
    In the wake of rapid glacial retreat, alpine habitats in the Arctic are expanding as freshly exposed surfaces become vegetated. Many glaciers in alpine cirques have nearly disappeared, and little is known about the rate of colonization or pioneer communities that develop following deglaciation. Newly developed habitats may provide refugia for sensitive Arctic flora and fauna, especially in light of polar warming. To assess this process, vegetation communities developing on two recently deglaciated moraines in the Central Brooks Range were surveyed and compared with communities along a transect spanning both a glacial chronosequence (40-125,000 years since deglaciation) and an elevation gradient (1700-500 m) into the Arctic foothills. Results show that primary succession begins almost immediately following deglaciation. Within forty years fine-grained and rock substrates hosted small communities of 8-13 vascular and nonvascular plant species. Many pioneer taxa, especially lichens, persist into later stages of succession. Overall succession is directional and slow, increasing in species richness for about 10,000 years, after which richness decreases and communities stabilize. This is the first vegetation study on primary succession in the high Central Brooks Range, providing a missing link to a vegetation transect along the Arctic Bioclimatic gradient.
  • 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.

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