One of the benefits of colonial living in insect societies is the ability to build a nest which enables the maintenance of a homeostatic microenvironment. The detrimental and uncertain effects of fluctuating ambient conditions are thus avoided. An extensive amount of work has documented the regulation of respiratory gases and temperature by honeybee (Apis mellifera) colonies but relatively little is known of their water relations. Nest humidity influences the fitness of the honeybee colony by affecting adult and brood mortality, microbial and parasitic growth, nectar concentration and thermoregulation. This study aims at determining whether honeybee colonies are able to actively regulate humidity within their nest or whether humidity is stabilised merely as consequence of other socially regulated parameters. As a first step in understanding water relations in a hive, the daily, seasonal and two-dimensional humidity patterns are described in diverse contexts: various subspecies, nest architectures, ambient climates and colony conditions. The humidity in the brood nest of a healthy honeybee colony does not show a daily pattern: mean hourly RH remains between 50 and 60 % and high vapour pressure deficit results in a large evaporative capacity. Two-dimensional humidity patterns show that a vapour pressure gradient exists from the central brood area to the periphery of a hive. This finding suggests possible active regulation by workers and to test this idea we determined the behavioural response of a group of workers to a humidity gradient. Young honeybee workers in the absence of brood exhibit a weak hygropreference for approximately 75% RH. When brood is present the expression of this preference is further weakened, suggesting that workers tend to the brood by distributing evenly in the gradient. In addition, fanning behaviour is shown to be triggered by increasing humidity adding to our understanding of this behaviour. Although these results suggest that humidity in honeybee colonies is actively controlled by workers, passive mechanisms are also involved in the observed patterns. Cocoons that are spun by the larvae accumulate in cells and these hygroscopic cocoons contribute to passive stabilisation of humidity. Old comb containing cocoons absorb 11 % of its own mass in water when placed in high humidity and this water can readily evaporate into the atmosphere when humidity decreases. This buffering effect may increase brood survivorship by maintaining a high and stable humidity in the brood cells. This study contributes to our understanding of the complex mechanisms that govern microclimatic regulation in social insect nests and specifically the active and passive mechanisms that ensure homeostasis of honeybee nest humidity. Copyright / Dissertation (MSc)--University of Pretoria, 2008. / Zoology and Entomology / unrestricted

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Effective coastal adaptation to sea-level rise requires an understanding of how much and how fast glaciers and ice sheets will melt in the coming decades, together with an understanding of the provenance of that ice melt. When land ice is lost to the oceans, sea-levels do not rise uniformly across the globe, but exhibit a “sea-level fingerprint” specific to the source of ice melt, posing an important question motivating this thesis: Which ice mass(es) will contribute the first 1m/3 feet of sea-level rise? The glacial-geologic record archives the vulnerability of ice sheets and their sub-sectors to past warming. To analyze this record of past glacial change, I develop and apply cosmogenic-nuclide techniques for investigating the climate sensitivity of four key ice sheets. The novel geochemical techniques described here also allow me to investigate processes of landscape evolution, including subglacial and subaerial erosion. Subglacial erosion dictates landscape development in glaciated and formerly glaciated settings, which in turn influences ice-flow dynamics and the climate sensitivity of ice masses, making it an important input in ice-sheet models. In Chapter 1, I use 10Be measurements in surficial bedrock and a 4-m-long bedrock near Jakobshavn Isbræ, to constrain the erosion rate beneath the Greenland Ice Sheet (GrIS) on historical and orbital timescales. 10Be concentrations measured below ~2 m depth in a 4-m-long bedrock core are greater than what is predicted by an idealized production-rate depth profile and I develop a model to utilize this excess 10Be at depth to constrain orbital-scale erosion rates. I find that erosion rates beneath GrIS were 0.4–0.8 mm yr-1 during historical times and 0.1–0.3 mm yr-1 on Pleistocene timescales. The broad similarity between centennial- and orbital-scale erosion rates suggests that subglacial erosion rates adjacent to Jakobshavn Isbræ have remained relatively uniform throughout the Pleistocene. In Chapter 2, I present cosmogenic 10Be and 3He data from Ferrar dolerite pyroxenes in surficial rock samples and a bedrock core from the McMurdo Dry Valleys, Antarctica, opening new opportunities for exposure dating in mafic rocks. I describe scalable laboratory methods for isolating beryllium from pyroxene, estimate a spallation production rate for 10Be in this mineral phase, referenced to 3He, of 3.6 ± 0.2 atoms g-1 yr-1, and present initial estimates for parameters associated with 10Be and 3He production by negative muon capture. I also demonstrate that the 10Be-3He pair in pyroxene can be used to simultaneously resolve exposure ages and subaerial erosion rates, and that the precision of my 10Be measurements in pyroxene enable exposure dating on Last Glacial Maximum to Late Holocene surfaces, including moraines, on a global scale. In Chapter 3, I apply exposure dating locally to investigate the Last Glacial Maximum (LGM) and initial deglaciation of the Laurentide Ice Sheet (LIS), the most dynamic continental ice sheet, in southern New England and New York City. I synthesize new and existing exposure age chronologies from moraines and other glacial deposits that span ~26 to 20.5 ka, and quantify retreat rates for the southeastern LIS margin. Initial retreat at <5 to 30 m yr-1 started within the canonical LGM period, representing the slowest LIS retreat rates of the entire New England deglacial record, which I relate to a slow rise in modeled local summer temperatures through the LGM. Employing similar exposure dating techniques in Chapter 4, I describe the first 10Be ages from nunataks of the Juneau Icefield (JIF), Alaska, that I collected through the Juneau Icefield Research Program (JIRP) in order to evaluate icefield thinning during the Late Glacial and Holocene. I find that the JIF was smaller-than-present under warm climate conditions during the early-to-mid Holocene, elucidating the sensitivity of the icefield to warming. Tackling the climate crisis more broadly and in turn, addressing pressing Earth science questions like those posed in this dissertation, requires diverse perspectives. Yet, the Earth sciences have historically been among the least diverse of the STEM disciplines. As one contribution to a comprehensive effort through JIRP to increase diversity in the geosciences pipeline, Chapter 5 details the curriculum for a two-week course titled ‘A Virtual Expedition to the Juneau Icefield’ that I co-designed and co-taught in 2021 to bring accessible polar science experiences to high school students.

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The impact of in vitro ozone and sulfur dioxide fumigation on pollen from two Fraser fir populations was examined. Populations were located at Mt. Rogers, Va, and Mt. Mitchell, S.C.. Two age groups "young" (less then 30 years old) and "old" (more then 40 years old) were examined within each population. No statistically significant age group differences in pollen germination percentage or pollen tube length were found. Mt. Mitchell pollen had a higher germination percentage than Mt. Rogers population. The statistically significant differences in pollen germination between populations were most probably due to the confounding effect of collection practices, and environmental conditions during 1986 pollen collection, rather than actual differences between populations. In vitro pollen fumigation with sulfur dioxide had no impact on pollen germination while fumigation with ozone decreased pollen germination percentage but did not change pollen tube length. Most of the variation in pollen germination percentage, and pollen tube length was due to genotype of the pollen parent tree. The phenotypic expression of six isozymes (previously correlated with resistance to air pollutants) in pollen was studied using polyacrylamide gel electrophoresis. The pattern of isozyme distribution among pollen phenotypes confirmed results from pollen germination studies. There was a difference between locations but no difference between age groups. None of isozyme phenotypes was correlated with a "resistance" to pollen fumigation with ozone or sulfur dioxide. / Master of Science

This thesis addresses the problem of predicting satellite path rain fade duration statistics for an arbitrary location, frequency, elevation angle and polarization. It summarizes the development of a dynamic stochastic model. From this model a technique is derived for predicting fade duration statistics for one site using measured attenuation data at another site. This technique is evaluated by comparing predicted and experimental results for several locations, frequencies, elevation angles and polarizations. / M.S.

Atmospheric carbon dioxide levels have been steadily increasing from anthropogenic energy production, development and use. Carbon cycling in the terrestrial biosphere, particularly forest ecosystems, has an important role in regulating atmospheric concentrations of carbon dioxide. US West coast forest management policies are being developed to implement forest bioenergy production while reducing risk of catastrophic wildfire. Modeling and understanding the response of terrestrial ecosystems to changing environmental conditions associated with energy production and use are primary goals of global change science. Coupled carbon-nitrogen ecosystem process models identify and predict important factors that govern long term changes in terrestrial carbon stores or net ecosystem production (NEP). By quantifying and reducing uncertainty in model estimates using existing datasets, this research provides a solid scientific foundation for evaluating carbon dynamics under conditions of future climate change and land management practices at local and regional scales. Through the combined use of field observations, remote sensing data products, and the NCAR CESM/CLM4-CN coupled carbon-climate model, the objectives of this project were to 1) determine the interactive effects of changing environmental factors (i.e. increased CO���, nitrogen deposition, warming) on net carbon uptake in temperate forest ecosystems and 2) predict the net carbon emissions of West Coast forests under future climate scenarios and implementation of bioenergy programs. West Coast forests were found to be a current strong carbon sink after accounting for removals from harvest and fire. Net biome production (NBP) was 26 �� 3 Tg C yr�����, an amount equal to 18% of Washington, Oregon, and California fossil fuel emissions combined. Modeling of future conditions showed increased net primary production (NPP) because of climate and CO��� fertilization, but was eventually limited by nitrogen availability, while heterotrophic respiration (R[subscript h]) continued to increase, leading to little change in net ecosystem production (NEP). After accounting for harvest removals, management strategies which increased harvest compared to business-as-usual (BAU) resulted in decreased NBP. Increased harvest activity for bioenergy did not reduce short- or long-term emissions to the atmosphere regardless of the treatment intensity or product use. By the end of the 21st century, the carbon accumulated in forest regrowth and wood product sinks combined with avoided emissions from fossil fuels and fire were insufficient to offset the carbon lost from harvest removals, decomposition of wood products, associated harvest/transport/manufacturing emissions, and bioenergy combustion emissions. The only scenario that reduced carbon emissions compared to BAU over the 90 year period was a 'No Harvest' scenario where NBP was significantly higher than BAU for most of the simulation period. Current and future changes to baseline conditions that weaken the forest carbon sink may result in no change to emissions in some forest types. / Graduation date: 2013

Lichens are an important part of the biota in western Oregon forests, where they perform valuable ecological roles and contribute significantly to biodiversity. Lichens in western Oregon are threatened by a number of factors including air pollution and land use practices. If we wish to maintain the persistence of lichens in future landscapes it is critical that we understand the responses of lichen communities and individual lichen species to the environment and forest structure. This dissertation explores factors that are related to differences in lichen community composition and the distributions of individual lichen species in the western Cascades of Oregon, using a large landscape scale data set. I sought to relate major gradients in lichen community composition to environmental factors, and describe differences in lichen communities with respect to forest age (Chapter 2). I found three major gradients in lichen communities at a landscape scale in the western Oregon Cascades. These gradients were related to climate as expressed by elevation and annual temperature, air quality, north-south position, the richness of epiphytic macrolichens, and forest age. I developed a rarity score, which can be used to identify hotspots of rare species diversity at a landscape scale (Chapter 3). I then built descriptive models of this rarity score to identify abiotic and biotic factors associated with the occurrence of rarity hotspots. I found that models of rarity score that used explanatory variables based on lichen community composition performed better than models that used explanatory variables based solely on environmental factors. I narrowed my focus to the level of individual species responses to the environment and forest structure by developing habitat models for 11 lichen species in the western Cascades (Chapter 4). We selected these species because they performed important ecological roles, were rare across the landscape and associated with old growth forests, or because their distributions were poorly understood. These models can be used to increase the efficiency of landscape level surveys for rare species, predict the response of these species to forest management practices, and understand factors associated with the distributions of these lichens. / Graduation date: 2006