Browsing by Subject "stable isotopes"

Now showing 1 - 4 of 4
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    Estimating natal origins and migratory patterns of juvenile raptors banded during fall migration at Hawk Ridge Duluth, MN
    (2022-08) Pavlovic, Emily
    Effective conservation of migratory species requires knowledge of the many geographic locations utilized during their full annual cycle. Determining breeding location can be challenging due to the secretive nature of many raptors on their breeding grounds; however, during migration, these species are relatively easy to study since large numbers of individuals fly through migration corridors. The objective of this research was to improve our understanding of full annual cycle landscape use by identifying the breeding origin and migratory patterns of juvenile raptors utilizing hydrogen stable isotope analysis of feathers (ẟ2Hf) collected during fall migration at Hawk Ridge in Duluth, Minnesota. We found that ẟ2Hf was able to elucidate temporal migration patterns and broadly assign natal origins. However, assignments remain broad and could be improved by the addition of other techniques. Knowledge of breeding locations and migratory patterns is important for connecting ecological variables on breeding grounds to observed population changes during migration and placing Hawk Ridge’s long-term monitoring data within a geographical framework.
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    Evaluating how spatial heterogeneity in forage chemistry and abundance influences diet and demographics in a declining moose (Alces alces) population in northeast Minnesota.
    (2019-05) Berini, John
    Since 2006, the moose population in northeastern Minnesota has declined by nearly 50%. While recent warming has been implicated as a primary cause of this decline, there is little evidence to support this relationship. More recent evidence suggests that the influences of warming and poor nutrition may predispose moose to increased risk of mortality, including mortality attributed to predation and disease. During summer, moose begin to experience the detrimental effects of high temperatures at around 14 to 17 ºC, and mean-maximum summer temperatures in this area range from 19.5 ºC along Lake Superior, to approximately 24.5 ºC in the more central part of the region. Thus, moose in northeastern Minnesota are likely dealing with the negative effects of high temperatures on a routine basis throughout summer. While it has been suggested that nutrition and warming may be acting in concert to influence moose demographics in Minnesota, potential synergisms between these factors have not been investigated. Thus, I evaluated how spatial variation in the thermal landscape influences forage chemistry, the abundance and distribution of forage, and the spatial variation in moose diets and overwinter survival. To determine how high temperatures might influence the chemistry of moose forage, I used untargeted metabolomics to evaluate how varying combinations of temperature, moisture, and light in both experimental and natural conditions influence the production of plant secondary metabolites in moose forage. To investigate how the abundance and chemistry of moose forage varies across NEMN, I used a mixed-effects regression kriging framework to estimate spatial variation of δ13C and δ15N values in plants commonly eaten by moose, and then refined these predictions using species-specific allometric equations to estimate above-ground biomass of moose forage. Finally, to investigate the interaction between spatial variation in high summer temperatures, moose diet, and over-winter survival, I used stable isotope values from forage and hair to estimate moose diet via Bayesian mixing models, and then evaluated if diet composition and quality vary as a function of mean-maximum summer temperature, season, or winter mortality. In general, warming and high-temperatures had variable effects on the defensive chemistry of moose forage, only a minor influence on forage abundance, and a strong effect on diet quality, composition, and overwinter survival. Specifically, when investigating the influences of warming on PSM production in moose forage, I found that the influences of temperature can be modulated by the presence or absence of other abiotic factors, such as precipitation and light. As an example, the relative abundance of compounds known to negatively influence moose herbivory increased by 250% or more when high temperatures occurred in an open canopy setting. When modeling spatial heterogeneity in the chemistry and abundance of moose forage across northeastern Minnesota, I found that while mean-maximum summer temperature played a strong role in the isotopic composition of moose forage across the region, it had only a minor effect on distribution and abundance. Finally, when investigating interactions between spatial variation in high summer temperatures, moose diet, and over-winter survival, I found that the warmest parts of the moose range in Minnesota were those where moose diets were poorest and where winter mortality rates were highest. Specifically, I found that moose in the warmest parts of the range have diets containing the highest proportion of aquatic forage and the lowest proportion of high-preference forage. Additionally, moose that did not survive winter had diets containing substantially greater proportions of aquatic forage throughout the entire growing season when compared to moose that survived, which consumed mostly high-preference forage during early summer but increased their consumption of aquatics during late summer. Finally, while I estimated overall mortality to be at approximately 30% throughout the entire study region, mortality in the warmest parts of the range (69%) was approximately 4.5 times higher than that in the coolest parts of the range (15%). Given the evidence I present here, habitat-improvement projects may want to focus on promoting the regeneration of forage species that can adapt to future warming scenarios, while still providing thermal refuge, and proper nutrition during late summer. Also, future studies should evaluate spatially explicit differences in habitat use as a function of the thermal landscape and how variation in habitat use-behavior (i.e., movement) within the thermal landscape may influence diet composition, quality, and nutritional restriction. Identifying mechanistic links between movement, diet, and nutritional condition within the thermal landscape would advance our basic knowledge of large mammal behavior and ecology, as well as help develop sound management strategies in how we plan for future warming.
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    Isotopic Signatures of Precipitation and Streams along the North Shore of Lake Superior
    (2019-06) Stoll, Kinzey
    Lake Superior is the largest of the Great Lakes. Its size impacts precipitation along the North and South Shores, but the magnitude of its effects on the North Shore are unknown. Using stable isotopes of δ2H and δ18O to understand the source and transport of precipitation allows us to develop a deeper understanding of the hydrologic cycle in the region and the possible impact of the lake on precipitation. Samples were collected from five snow storms from November 2017 to March 2018, snowmelt from April 2018, and streamflow from May to August 2018. To further examine the hydrologic cycle along the North Shore, the Lester River watershed was studied for spatial and temporal variations from May to December 2018. This watershed, like many others along the North Shore, is a designated trout stream. Water samples collected from the stream and from precipitation were used to show seasonal trends and spatial variability across the watershed. This information highlights the timing of different processes in the watershed such as evaporation. Temperature data was also collected throughout the watershed to show conditions for trout and provide more information on hydrologic processes.
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    New insights into Great Basin hydroclimate: past and present
    (2016-05) Cross, Mellissa
    From thermodynamic principles, Held and Soden (2006) predicted that in a globally warming world, dry places become drier, and wet places wetter; or by contrapositive, dry places become wetter in a globally cooling world. This hypothesis holds profound implications for our increasingly warmer Earth and vital water resources. The magnitude of this drying and whether it holds true on regional scales, however, is not clear. To explore this further, there are two options: we can model the future, or reconstruct the past. This thesis is an exploration of the past and present regional hydroclimate of the Great Basin. The Great Basin region is a large internally drained area in the western United States that has experienced significant hydroclimate changes. Large interbasin freshwater lakes dominated the landscape during glacial periods, and much time and effort has been expended understanding the timing and causes of lake level fluctuations. Until recently, there was a relatively poor understanding of Great Basin hydroclimate in times beyond the reach of radiocarbon dating. The Devils Hole record added another layer of uncertainty by indicating a Termination II ( T-II ) at least 10,000 years earlier than insolation rise. After nearly 30 years, a new Devils Hole record offers a promising reconciliation with orbital theory, indicating that certain geochemical and hydrological processes may have caused the older apparent ages of the original record. However, many aspects of Great Basin hydroclimate change are uncertain. As such, I explore two new records of Great Basin hydroclimate from Lehman Caves, Nevada, speleothems in this work. Speleothems are cave formations, which can be dated very precisely using the uranium-thorium radio-isotope system and have a number of chemical and isotopic parameters that can be interpreted to represent response to various facets of climate. For each record, both temperature and potentially a seasonal precipitation contribution change response, using δ 18 O values, and a hydroclimate response, using δ 13 C values, Mg/Ca, and Sr/Ca ratios (in Chapter 4), or transition metals and rare earth elements (in Chapter 5) are explored. Overall, Held and Soden (2006)’s prediction holds true. However, on shorter time scales climate response is more complicated, and millennial-scale events in the North Atlantic can influence moisture delivery to the Great Basin such that hydrologic changes do not always occur in lockstep with temperature variations. I further examine the potential for a hydrologic signal in my δ 18 O record by combining modern trajectory analysis with precipitation isotope data.