Now showing items 1-20 of 62

• #### Arctic Alaskan Shrub Growth, Distribution, And Relationships To Landscape Processes And Climate During The 20Th Century

The primary change underway in the tundra of Arctic Alaska is the increase in air temperature and expansion of deciduous shrubs since 1980. I explored relationships between shrub expansion and relevant ecosystem properties such as climate, soil characteristics, erosion, and herbivory. Alnus viridis ssp. fruticosa (Siberian alder) shrubs located along streams, rock outcrops, or other features with active disturbance regimes showed a positive correlation between growth ring widths and March through July air temperature. Climate-growth relationships were much weaker for alder in adjacent tussock tundra. Additionally, tussock tundra sites had different vegetation composition, shallower thaw, lower mean annual ground temperature, lower mean growing season temperature, higher soil moisture, more carbon in mineral soil, and higher C:N values in shrub leaves than nearby non-tussock alder. Growth rings and site characteristics imply that preexisting soil conditions predispose alder shrubs growing in non-tussock tundra to respond rapidly to warming. Analysis of temporal series of aerial photography from 1950 and 2000 and of Landsat imagery from 1986 and 2009 showed an increase in percent cover of shrubs, primarily in riparian areas. This increase in shrubs is contemporaneous with a decline in peak discharge events from the Kuparuk River and a lengthening of the growing season since 1980, both of which may have caused the decline in sediment deposition observed in 3 of 4 lake sediment cores dated with lead and cesium isotopes. Both alder shrub growth and erosion are particularly sensitive to runoff dynamics during the snowmelt and green-up period, and these dynamics are affected by spring temperatures. Ptarmigan, moose, and hares forage heavily on shrubs protruding above the deepening snow during the late-winter, and selective browsing on willow vs. alder is likely influencing shrub community composition. The increase in shrubs during the 20th century may represent additional habitat for these herbivores, and herbivore-mediated changes in shrub architecture may have important implications for how shrubs trap snow and ultimately affect surface energy balance. Evidence from this thesis indicates shrub growth and cover have increased in response to persistent warming, particularly in areas where the organic layer is thinner and active layer deeper.
• #### Biocomplexity Of Nonsorted Circles In The Low Arctic, Alaska

The vegetation and soils in many arctic tundra regions are influenced by the distribution of nonsorted circles, unique patterned-ground features that dot the well-vegetated tundra landscape. They are flat to dome-shaped, bare soil patches 0.5 to 3 m across and lack a border of stones. Localized soil disturbance due to cryogenic processes creates unusual micro-environments with unique plant communities, slow soil development and deep active layers. The contrast between barren nonsorted circles and the well-vegetated stable tundra provides an ideal opportunity to examine the complex linkages among vegetation, soil and disturbance through cryogenic processes, offering insight into how the tundra system operates. The central goal of this thesis is to understand the complex linkages of the nonsorted-circle system along a natural climate gradient on the North Slope in the Alaskan arctic tundra at different scales, ranging from plot level to regional changes. This thesis examines the interactions among vegetation, soil and cryogenic regime by treating the nonsorted circles within the stable tundra as a single complex system. The thesis presents a formal description and analysis of the plant communities on and off nonsorted circles along the climatic gradient using Braun-Blanquet classification approach. The thesis also studies the physical effects of vegetation, soil organic mat and snow cover on the microclimate of nonsorted circles and the stable tundra along the same climate gradient. The influence of vegetation on cryogenic processes is examined experimentally by manipulating the plant canopy on nonsorted circles. When compared to the stable tundra, nonsorted circles have minimal vegetation cover, resulting in warm soil temperatures and deep thaw depths in summer and allowing for increased ice-lens formation during freeze-up. The resulting frost heave and needle-ice formation at the soil surface maintain the bare surfaces of the circles through soil disturbance. Cryogenic processes dominate the system at the northern sites, while the warmer climate towards the south allows for thick vegetation mats on and off the nonsorted circles, suppressing cryogenic processes. The strength of the interactions among vegetation, soil and cryogenic regime may change under a warming arctic climate, possibly leading to the local disappearance of nonsorted circles.
• #### Bridging the gap between pupping and molting phenology: behavioral and ecological drivers in Weddell seals

In Antarctica, the narrow window of favorable conditions constrains the life history phenology of female Weddell seals (Leptonychotes weddellii) such that pupping, breeding, foraging, and molting occur in quick succession during summer; however, the carry-over effects from one life history event to another are unclear. In this dissertation, I characterize the phenological links between molting and pupping, and evaluate feeding behavior and ice dynamics as mechanistic drivers. First, I review the contributions of natural and sexual selection to the evolution of molting strategies in the contexts of energetics, habitat, function, and physiology. Many polar birds and mammals adhere to an analogous biannual molting strategy wherein the thin, brown summer feathers/fur are replaced with thick, white winter feathers/fur. Polar pinnipeds are an exception to the biannual molting paradigm; most rely on blubber for insulation and exhibit a single molt per year. Second, I describe the duration and timing of the Weddell seal molt based on data from 4,000 unique individuals. In adult females, I found that successful reproduction delays the molt by approximately two weeks relative to non-reproductive individuals. Using time-depth recorder data from 59 Weddell seals at the crucial time between pupping and molting, I report a striking mid-summer shallowing of seal dive depths that appears to follow a vertical migration of fishes during the summer phytoplankton bloom. The seals experience higher foraging success during this vertical shift in the prey distribution, which allows them to re-gain mass quickly before the molt. Across four years of study, later ice break-out resulted in later seal dive shallowing and later molt. In combination, the data presented in this dissertation suggest that molting, foraging, and pupping phenology are linked in Weddell seals and are affected by ice break-out timing.
• #### Carbon Sequestration In Alaska's Boreal Forest: Planning For Resilience In A Changing Landscape

Northern ecosystems and those who rely upon them are facing a time of unprecedented rapid change. Global boreal forests will play an important role in the feedback loop between climate, ecosystems, and society. In this thesis, I examine forest carbon dynamics and the potential for carbon management in Interior boreal Alaska in three distinct frameworks, then analyze my results in the context of social-ecological resilience. In Chapter 1, I analyze comparative historical trends and current regulatory frameworks governing the use and management of boreal forests in Russia, Sweden, Canada, and Alaska, and assess indicators of socio-ecological sustainability in these regions. I conclude that low population density, limited fire suppression, and restricted economic expansion in Interior Alaska have resulted in a 21st-century landscape with less compromised human-ecosystem interactions than other regions. Relative wealth and a strong regulatory framework put Alaska in a position to manage for long-term objectives such as carbon sequestration. In Chapter 2, I model the landscape-level ecological possibilities for sequestration under three different climate scenarios and associated changes in fire and forest growth. My results indicate that Interior Alaska could act as either a weak carbon source or as a weak sink in the next hundred years, and that management for carbon credits via fire suppression would be inadvisable, given the associated uncertainty and risks. In Chapter 3, I perform a social, ecological, and economic analysis of the feasibility of switching from fossil fuels to wood energy in Interior Alaska villages. I demonstrate that this is a viable option with the potential benefits of providing lower-cost power, creating local employment, reducing the risk of catastrophic wildfire near human habitation, and earning marketable carbon credits. Finally, in Chapter 4, I assess how each of the above factors may impact social-ecological resilience. My results show some system characteristics that tend to bolster resilience and others that tend to increase vulnerability. I argue that in order to reduce vulnerability, management goals for Alaska's boreal forest must be long-term, flexible, cooperative, and locally integrated.
• #### Cytogenetics and sex determination in collared lemmings

Collared lemmings (Dicrostonyx groenlandicus rubricatus) from northeastern Alaska were found to have sex chromosomes that differ from those of their Siberian congeners, because of fusion to a particular pair of autosomes. But, as in Siberian lemmings, breeding experiments showed that sex determination involves an X-linked "male-repressor," which causes carriers to develop as fertile females, despite the presence of a Y chromosome. Genotypic frequencies in offspring are consistent with Mendelian expectations of such a system, hence natal sex ratios normally favor females. X-linkage of the male-repressor in Siberia and in Alaska indicates that the gene is probably located on the "original" arms of the X chromosome rather than on the fused autosomal arms, which differ on the two continents. One consequence of the autosomal fusion to the sex chromosomes is that deleterious recessive alleles on the autosome fused to the X chromosome are more resistant to selection than at truly autosomal loci. Another consequence is that, because males are heterozygous for loci fused to the sex chromosomes, they are more resistant to inbreeding depression than XX females. One inbred line produced a natal sex ratio of 67% males. The male-bias probably resulted from loss of the male-repressor and from a lethal carried on the formerly autosomal arm of the X chromosome. As inbreeding coefficients approached 0.3, the lethal would have been homozygous in half of the homogametic (female) zygotes. This phenomenon may explain the excess of males and XY females observed in earlier work. Also, if under the natural mating system, inbreeding depression limits fitness, then fusions of autosomal chromatin to the heterochromosomes could be an adaptation to reduce inbreeding depression in heterogametic individuals. Some other genetic features of collared lemmings do suggest endogamy. Female-biased sex ratios can evolve when mating occurs between neighboring individuals who are more related than if mating occurred randomly. Two proposed sources of such "viscous" gene flow in lemmings are cyclical changes in population density and mosaic habitat. Alternatively, could climate may favor winter aggregation and inhibit the dispersal of winter-born offspring, which would mature and mate with close relatives; dispersal and outbreeding would occur in summer. Thus, inbreeding would be seasonal rather than density-dependent and it is unnecessary to suppose discontinuous habitat.
• #### Ecogeographic, Adaptive, And Phylogenetic Variations In The Crested Duck (Lophonetta Specularioides) And Their Hemoglobins In The Andes

Tolerance to high-altitude hypoxia in animals varies widely and is a key factor in determining survival at high elevation. The Andean Cordillera of South America, which spans large elevational and latitudinal gradients, enables the study of native highland populations and the characteristics of hemoglobin proteins that are locally adapted for high-altitude respiration. The waterfowl populations of South America are understudied, little data on demographics and behavior are currently available, and only recently have they been investigated using molecular tools. We studied population genetics, phylogeography, and ecogeographic variation in the crested duck ( Lophonetta specularioides). The crested duck is a dabbling duck, and it comprises two subspecies endemic to highland and lowland regions of South America. The primary objective of this study was to investigate the genetic differentiation between highland and lowlands populations of crested ducks using molecular markers with varying modes of inheritance and rates of substitution. The second objective was to evaluate morphological differences between the subspecies to better understand the forces shaping morphology in the two different environments. A third objective was to provide additional information on the taxonomic relationships and natural history of the crested duck. First, we examined the population genetics of the three adult hemoglobins (alphaD, alphaA, betaA), six autosomal introns, and mtDNA. This multi-locus analysis revealed a significant pattern of differentiation between highland and lowland populations. Four hemoglobin amino acid replacements were found in crested duck that may play a role in influencing high-altitude respiration. The lack of evidence for gene flow for hemoglobin alleles between highland and lowland populations and the biochemical properties of the amino acid substitutions themselves are consistent with the effects of selection acting on these loci. Overall body size was larger for the highland subspecies, body size was intermediate in mid-elevation environments, and smaller individuals were found in the lowlands of Patagonia. We also performed a multi-locus phylogenetic analysis to determine the relationships of Lophonetta within the South American duck clade. Finally, we determined the proportion of genes expressed in bone marow of adult crested duck finding mostly genes related to hemopoietic and immune function.
• #### Ecological And Physiological Adaptations Of The Porcupine To Winter Alaska

Understanding the ecology and physiology of wildlife is paramount to conservation and management of species. North American porcupines (Erethizon dorsatum) are mammalian herbivores that occupy a diverse array of habitats across a broad geographical range. However, few studies have explored the ecology and physiology of porcupines. I used captive and free ranging porcupines to 1) identify the physiological abilities that enable them to survive on low quality winter forage when thermoregulatory demands are high, 2) determine responses of porcupines to winter conditions, and 3) determine how winter conditions influence habitat selection and home range size at the northern limits of their range. My research revealed that the persistence of porcupines at the northern limits of their range is due to plasticity of food intake, as well as physiological tolerance of low-quality diets and low ambient temperatures. Captive porcupines gained mass when high quality diets were available. However, porcupines decreased their dry matter intake throughout winter, indicating a seasonal decrease in metabolic rate. Low requirements for energy and nitrogen minimized the loss of body mass when intakes were low, while plant toxins increased urinary losses of energy and nitrogen. Free-ranging porcupines conserved lean body mass in winter by catabolizing fat stores. Proportional fat loss was correlated positively with total fat mass at the start of winter. Fat losses were minimized by lowering rates of energy expenditure. Water turnovers were slow in wild porcupines and body temperatures were not reduced to save energy. In order to survive winter on a low quality diet of white spruce (Picea glauca ) needles and cambium and paper birch (Betula papyrifera ) cambium, porcupines maintained large home ranges comprised primarily of mixed conifer/hardwood forests. Occupying a mixed forest habitat allowed porcupine to switch their diet between two forage tree species, potentially alleviating saturated detoxification pathways. Overall, porcupines possess the physiological abilities of a specialist herbivore during winter; however, they rely on abundant high quality summer forages to replenish their stores of fat and protein for reproduction and survival in the subsequent winter.
• #### Ecological And Social Influences On Population Dynamics And Genetics Of Moose In Alaska

I examined social and ecological influences on moose (Alces alces gigas) in Alaska, USA, with respect to hunting success, antler size, and population genetic structure. Catch per unit effort (CPUE) is frequently used to assess hunter success; thus I hypothesized that landscape characteristics and moose density would affect success. Using hunter harvest tickets returned to the Alaska Department of Fish and Game, I modeled CPUE with Weibull regression. I determined success is significantly predicted by hunt location, mode of transportation, hunting regulations, use of commercial services (i.e., guides), year, road density, hunter-to-moose ratio, moose density, and hunter residency status. Antler size is an important factor for hunters and for mating potential in male moose. I hypothesized that moose density, habitat, and use of guides would correlate with antler size of harvested moose. I also predicted that guides would harvest moose with larger antlers and avoid areas where the hunter-to-moose ratio is high compared to nonguided hunters. Results indicated that antler size decreases with increases in moose density and harvest intensity due to density-dependent processes and a younger age structure in heavily harvested areas. Guided hunts tended to harvest larger antlered bulls and avoided areas of high hunter-to-moose ratios. In addition to age and nutrition, genetics influences antler size. I used eight microsatellites and five sample areas to resolve whether population structure exists among moose in Alaska. I hypothesized that population structure does exist given the intense harvest rates, polygynous mating style of moose, and heterogeneous landscape present in Alaska. Dispersal and gene flow between populations was proposed to occur via isolation-by-distance (IBD) with a positive linear relationship between geographic and genetic distance. Results indicated weak but significant population structure for moose in Alaska, and IBD was supported. Pairwise comparisons between populations indicated that moose have established separate populations except for between Tanana Flats and Koyukuk and Koyukuk and the Seward Peninsula. Lastly, I hypothesized incorporation of landscape characteristics and subsequent least-cost path would strengthen the significance of IBD. With an additional population, Tetlin, the significance of IBD as a mechanism for dispersal/gene flow for moose in Alaska was improved.

• #### Ecology of a reestablished population of muskoxen in northeastern Alaska

The restoration of muskoxen (Ovibos moschatus) to regions of former range in northeastern Alaska presented an opportunity to study population dynamics, seasonal patterns, and dispersal in an expanding population of ungulates. Muskoxen were returned to the Arctic National Wildlife Refuge (Arctic NWR) in 1969-70 after an absence of $>$100 years. In 1982-97, I used annual censuses, counts by sex and age, radio and satellite telemetry, and data from Landsat-TM maps to determine rates of population growth, changes in production, survival, and group size over time, seasonal habitat use, activity patterns, and dispersal of mixed-sex groups. In 1982-86, mixed-sex groups of muskoxen occupied the same regions as in 1977-81, but annual rates of increase and calf production declined (1977-81: rate = 0.24, 87 calves/100 adult females; 1982-86: rate = 0.14, 61 calves/100 adult females). In 1987-95, numbers of muskoxen in regions first occupied declined and stabilized at $<$300 animals as calf production continued to decline and mixed-sex groups dispersed into unoccupied regions. Survival of calves and yearlings did not decline over time. By 1995, about 800 muskoxen were distributed between the Itkillik River west of Prudhoe Bay, Alaska, and the Babbage River in northwestern Canada. In summer, female muskoxen occupied large core areas $(\bar x=223$ km$\sp2),$ and had high rates of movement $(\bar x=2.6$ km/day) and activity $(\bar x=18.9$ counts/min). In winter muskoxen remained in small core areas (mid-winter $\bar x=25$ km$\sp2)$ and reduced movements (mid-winter $\bar x=1.4$ km/day) and activity (mid-winter $\bar x=11.8$ counts/min.) possibly as a strategy to conserve energy. Muskoxen selected (use $>$ availability) riparian and moist sedge vegetation along rivers in all seasons. Dispersal of mixed-sex groups occurred infrequently through periodic pulses. Population density likely influenced patterns of dispersal through social interactions and habitat change. Weather conditions that affected the length of the growing season and availability of winter forage were major factors in the dynamics, distribution, and dispersal patterns of this reestablished population of muskoxen.
• #### Ecology of Prince of Wales spruce grouse

Recently, spruce grouse on Prince of Wales Island (POW) in southeast Alaska have been proposed as a separate subspecies. Furthermore, life-history of spruce grouse on POW, which is temperate coastal rainforest, varies sufficiently from birds in mainland areas, mostly boreal forest, to warrant specific management. Therefore, I examined the ecology of spruce grouse on POW to determine how timber harvest influences their survival and habitat selection and ultimately to provide recommendations for their conservation. During 2007-2009, we found that the greatest variation in survival probability was attributed to breeding status. The annual survival of non-breeding birds was 0.72±0.082 (S±) while for breeding birds it was 0.08±0.099. Logging did not adequately predict survival, with no differences among habitats. Conversely, I found differences in selection among habitats. At the watershed scale, spruce grouse preferred unharvested forest. At both watershed and homerange scales, spruce grouse avoided edges and preferred roads. Road-related mortality was the largest known source of death. POW spruce grouse and mainland subspecies exhibit sufficiently different survival rates and habitat preference to warrant specific management. We recommend limited road closures during periods when POW spruce grouse are most vulnerable due to the high rates of mortality associated with this preferred habitat.
• #### The effects of permafrost degradation on soil carbon dynamics in Alaska's boreal region

High-latitude regions store large quantities of organic carbon (C) in permafrost soils and peatlands, accounting for nearly half of the global belowground C pool. Projected climate warming over the next century will likely drive widespread thawing of near-surface permafrost and mobilization of soil C from deep soil horizons. However, the processes controlling soil C accumulation and loss following permafrost thaw are not well understood. To improve our understanding of these processes, I examined the effects of permafrost thaw on soil C dynamics in forested upland and peatland ecosystems of Alaska's boreal region. In upland forests, soil C accumulation and loss was governed by the complex interaction of wildfire and permafrost. Fluctuations in active layer depth across stand age and fire cycles determined the proportion of soil C in frozen or unfrozen soil, and in turn, the vulnerability of soil C to decomposition. Under present-day climate conditions, the presence of near-surface permafrost aids C stabilization through the upward movement of the permafrost table with post-fire ecosystem recovery. However, sensitivity analyses suggest that projected increases in air temperature and fire severity will accelerate permafrost thaw and soil C loss from deep mineral horizons. In the lowlands, permafrost thaw and collapse-scar bog formation resulted in the dramatic redistribution of soil water, modifying soil thermal and C dynamics. Water impoundment in collapse-scar bogs enhanced soil C accumulation in shallow peat horizons, while allowing for high rates of soil C loss from deep inundated peat horizons. Accumulation rates at the surface were not sufficient to balance deep C losses, resulting in a net loss of 26 g C m⁻² y⁻¹ from the entire peat column during the 3000 years following thaw. Findings from these studies highlight the vulnerability of soil C in Alaska's boreal region to future climate warming and permafrost thaw. As a result, permafrost thaw and soil C release from boreal soils to the atmosphere should function as a positive feedback to the climate system.
• #### Experimental And Theoretical Studies Of The Pollination Ecology Of Gynodioecy

Gynodioecy, a breeding system with females and hermaphrodites, is the most common dimorphic system in plants and found in more species than all other polymorphic systems combined. One unresolved question in gynodioecy evolution is how dramatic sex ratio variation (0-100% female) is maintained among populations. To address this gap, I used complementary empirical and theoretical approaches to ellucidate pollinators' role in the evolution and maintenance of gynodioecy and variation in gynodioecious sex ratios. I conducted two field studies restricting the types of pollinators available to artificial populations of Silene vulgaris. The first study contrasted pollination by pollen collectors, strongly favoring hermaphrodites, with nectar collectors that readily visit both sexes. Hermaphrodites' relative fitness was greatest in the context of pollen collectors whereas females had dramatically higher relative fitness in the context of nectar collectors, demonstrating pollinators' potential to restrict or facilitate gynodioecy. The second study measured fitness in artificial populations of S. vulgaris with either pollen or nectar collecting pollinators in the context of a large natural population, providing access to more pollen sources and more pollinators. Female relative fitness was constant across pollination contexts, unlike in the previous study, as an abundance of pollinators and pollen sources diminished the differences in pollination contexts arising from pollinator bias. On the theoretical front, I developed mathematical models that describe female and hermaphrodite fitness in terms of pollinator abundance and behavior. Then, a single locus nuclear model of gynodioecious sex ratio evolution was used to describe equilibrium female frequency as well as the conditions permitting gynodioecy in terms of pollinator behavior. As in the field studies, I found that pollinators' influence could range from subtle to dramatic. More specifically, under realistic parameter values, where pollinators prefer hermaphrodites to females, incorporation of pollination ecology generally reduces female frequency, and the conditions for the evolution of gynodioecy become more stringent than if pollination processes were ignored. Together, these studies bolster the surprisingly overlooked idea that evolution of gynodioecious populations is directly influenced by pollinator context.
• #### Export Of Carbon, Nitrogen And Major Solutes From A Boreal Forest Watershed: The Influence Of Fire And Permafrost

Detailed observations of stream, soil, and groundwater chemistry were used to determine the role of fire, permafrost and snowmelt processes on the fluxes of carbon, nitrogen and major solutes from interior Alaskan catchments. We examined an experimentally burned watershed and two reference watersheds that differ in permafrost coverage (high, 53%; medium-burn, 18%; and low, 4%) during the FROSTFIRE prescribed burn in July 1999. The fire elevated stream nitrate concentrations for a short period during the first post-fire storm, but nitrate declined thereafter, suggesting that less severe fires that leave an intact riparian zone may have only a short-term effect on stream chemistry. Nevertheless, we found fundamental differences in hydrochemical differences between watersheds due to the presence of permafrost. Flowpaths in the low-permafrost, likely from the riparian zone, depleted stream nitrate levels while flowpaths in the high permafrost watershed, generated from more distant hillslopes, were a source of nitrate. All watersheds were sources of organic solutes during snowmelt and summer storms. On an annual basis, watersheds were net sources of every individual ion or element (Cl-, PO42- , SO42-, DOC, DON, NO3 -, Na+, K+ Mg2+, Ca2+) except NH4+, which was a small fraction of the total N concentration in streams. The concentration of NO 3- was high for an ecosystem with low atmospheric N deposition and compared to non-Alaskan boreal and temperate watersheds, resulting in net N loss. These findings suggest that boreal watersheds in the discontinuous region of interior Alaska may be fundamentally different in their capacity to retain N compared to ecosystems with net N retention.
• #### Factors affecting the growth of a black guillemot colony in northern Alaska

Annual variation in breeding populations at seabird colonies has been well documented, but there have been few long-term attempts to examine the environmental and demographic forces responsible. I studied breeding chronology and demography Black Guillemot in northern Alaska from 1975-1997 to identify the factors responsible for colony establishment and growth. The Black Guillemot is a cavity-nesting seabird whose populations are frequently limited by nest-site availability. Snowmelt in spring and snow accumulation in autumn had major effects on annual nesting initiation and success, respectively. Annual arrival at the colony and median date of egg laying was well correlated with the date of snow disappearance, with annual clutch initiation advancing 4.5 days per decade in response to regional climate amelioration. Successful breeding requires a snowfree cavity for ${>}80$ days. Decreased breeding success and post-fledging survival occurred in a year with a snow-free period ${<}80$ days. Historic weather records indicate annual snowfree periods ${>}80$ days were uncommon until the 1960's, when the species was first recorded breeding in northern Alaska. When additional nest sites were provided, growth of the colony was rapid, increasing from 18 pairs in 1975 to 225 pairs in 1989. Breeding numbers then decreased to 150 in 1996 as factors other than nest-site availability controlled population size.
• #### Fire And Successional Trajectories In Boreal Forest: Implications For Response To A Changing Climate

Because of the key role played by fire in structuring boreal forest ecosystems, interactions between vegetation and fire regime may be an important and dynamic control of forest response to climate change. This research uses a series of field observations and experiments in boreal forests to examine the nature of several potential fire and vegetation interactions, and how such interactions may influence forest response to climate change. Long-term observations of post-fire succession provide information on the timing of tree establishment and the effects of early establishment on subsequent successional trajectories. The role of competitive interactions in driving patterns of early establishment was tested with experimental manipulations of aspen (Populus tremuloides) cover after fire. This research demonstrated that competition by aspen re-sprouts may reduce the success of conifer establishment and favor long-term dominance by deciduous trees. The effects of fire severity on successional trajectories were tested in a series of field experiments that contrasted patterns of seedling establishment across differences in depth of the post-fire organic layer. All species in the experiment responded negatively to decreased fire severity, but deciduous trees were more sensitive in their response than conifers. Thus, variations in burn severity are likely to mediate deciduous establishment in organic-rich stands. Observations of natural tree regeneration in stands that burned at different ages also indicate that a decrease in fire interval can influence the relative abundance of deciduous and coniferous species by reducing conifer establishment. Over longer time scales, changes in biota caused by species migration may influence fire and vegetation interactions. Observations of post-fire regeneration at the current distribution limits of lodgepole pine (Pinus contorta) indicate that continued range expansion of pine could initiate rapid shifts in dominance from spruce to pine within a single fire cycle. Together, these results provide insight into the dynamic feedbacks between fire and vegetation that can lead to high levels of system resilience, while also promoting rapid responses when threshold conditions are crossed. A more complete understanding of these interactions will improve our ability to manage and predict boreal ecosystem responses to a changing climate.
• #### Foraging ecology and conservation biology of African elephants: Ecological and evolutionary perspectives on elephant-woody plant interactions in African landscapes

The available scientific evidence indicates that African forest elephants and bush elephants are ecologically and evolutionarily distinct taxa. The current practice of regarding these two taxa as ecotypes of a single species, Loxodonta africana (i.e., L. a. africana Blumenbach 1797, L. a. cyclotis Matschie 1900) appears unwarranted, and obscures issues of major significance to the conservation biology of African elephants. Under a proposed taxonomic revision, the African bush elephant retains the designation Loxodonta africana Blumenbach 1797 while the African forest elephant is recognized as Loxodonta cyclotis Noack 1906. The browsing of woody plants by African bush elephants is a major factor in the structural dynamics of semi-arid woodland and scrubland habitats in Hwange National Park (HNP) and the Sengwa Wildlife Research Area (SWRA), Zimbabwe. Drought, frost and fire also influence the structure and species composition of woody vegetation within HNP. Interactions among these three abiotic factors and elephant browsing may have significant impacts on the dynamics of semi-arid woodland and scrubland habitats of HNP. Mortality attributable to elephant damage was identified as a principal cause of death among large trees (>5.0 in height), and a relatively minor but not insignificant cause of death for shrubs and trees in the 1.0--5.0 in height class. The responses of Colophospermum mopane in SWRA to fertilization treatments corresponded to those predicted by the carbon/nutrient hypothesis of plant anti-herbivore defense. Comparisons of these results with those of previous studies suggest possible changes in the ecology and population biology of elephants in HNP during the past decade. Observed differences in the age-specific mortality of elephant in HNP during die-offs in 1993--1995 and 1980--1984 provide independent evidence of changes in the ecology of elephants in HNP during the period 1983--1993. The population of L. a. africana inhabiting the Matabeleland-Ngamiland-Okavango region of southern central Africa (which includes the HNP population), is the largest extant elephant population on Earth. The magnitude of this population (110,000--120,000), and the high proportion of its range currently under protection as wildlife reserves, indicate that this population may rank as the most viable and potentially sustainable elephant population on Earth.
• #### Foraging Ecology And Sociality Of Muskoxen In Northwestern Alaska

I investigated sociality and winter foraging ecology of muskoxen ( Ovibos moschatus) in Cape Krusenstern National Monument, northwestern Alaska. The nutritional value of moss (Hylocomium splendens, Tomenthypnum nitens) for muskoxen was evaluated by incubating moss in rumen-fistulated muskoxen and simulating post-ruminal digestion by incubation in acid-pepsin. Moss was indigestible in muskoxen and gained mass and nitrogen in the rumen. Consequently, high moss consumption during winter may result in net loss of nitrogen from a muskoxen's system. Local and regional differences in moss use by muskoxen and caribou or reindeer (Rangifer tarandus) were investigated in northwestern Alaska in relation to indicators of winter range quality. On muskox winter ranges, increases in fecal moss indicated decreased graminoid cover, harder snow, increased moss cover, and greater animal densities. Higher mobility of caribou than muskoxen during winter limits use of their feces to reflect local forage selection, but fecal moss may indicate caribou winter range quality on a larger, regional scale. Increasing proportions of moss in muskoxen feces may alert wildlife managers to shifts in forage availability due to changing snow conditions. Roles of male and female muskoxen in coordinating group movements were investigated during the snow-free season. Adult females led most activity initiations, foraging-bout movements, and spontaneous group movements. Rutting males actively manipulated female-led movements through herding and blocking. Leaders incurred no costs in terms of lost foraging time. Habitat use by muskoxen shifted from upland habitats in early summer towards lowland sedge meadows during rut. Muskox group sizes decreased from winter to summer to rut. Muskoxen foraging efficiency decreased with group size in spatially unlimited but not in spatially limited habitats. Adult males contributed least to group cohesion, and their presence may contribute to group fission during rut. A conceptual model is presented which discusses how habitat, foraging, social behavior, and predation threat contribute to group sizes, fission and fusion of muskox groups. Results from this study indicate that winter ranges used by muskoxen in Cape Krusenstern may be limiting, which suggests that numbers of muskoxen in this area will likely remain small. Therefore, hunting quotas should be low and limited to males only.
• #### Forest Ecology And Distribution Of Bats In Alaska

This thesis documents distribution of bat species in Alaska and effects of clearcutting on bat activity in temperate rainforests of southeastern Alaska. Occurrence of Myotis lucifugus, M. californicus, M. volans, M. keenii, and Lasionycteris noctivagans is confirmed in southeastern Alaska. I describe new specimens of M. keenii from southeastern Alaska, the first in over 100 years. Myotis lucifugus and Eptesicus fuscus are documented north of 64$\sp\circ$ N latitude. Environmental conditions and geography which influence distribution and latitudinal diversity gradients are discussed. Low bat activity in second-growth forests and clearcuts suggests that these areas provide little summer habitat. Higher activity levels in old-growth and riparian forests suggest these areas are important summer habitat. A change in activity between lactation and post-lactation periods is also noted. Unusual aspects of M. lucifugus ecology in southeastern Alaska are: consumption of spiders; presence of maternity colonies in a temperate rainforest; and intermittent use of hibernacula. <p>