Now showing items 874-893 of 3493

• The ecological genetics of gynodioecy in Silene acaulis L. (Caryophyllaceae): spatial sex structure and inbreeding depression

Gynodioecy, the co-occurrence of females and hermaphrodites, is considered an intermediate step in the evolution of separate sexes in flowering plants. Highly variable female frequencies among populations suggest structuring of sex determining genes and differences in the relative fitness of females and hermaphrodites as seed parents. I investigated spatial variability in sex ratio and the effects of inbreeding on offspring quality in Silene acaulis. Female frequencies varied among populations from 0.32 to 0.69, and most were at temporal equilibrium. Females were significantly clumped within two of six populations. Females produced from 4 to 27 times as many fruits as hermaphrodites. Self-pollination of hermaphrodites reduced offspring survivorship and growth by an average of 67% compared to outcrosses. Overall, spatial variation in female frequency suggests a role of founder events and local seed dispersal. Low fruit production and reduced quality of inbred offspring suggest hermaphrodites may be functioning primarily as pollen donors.
• Ecological interactions among important groundfishes in the Gulf of Alaska

Complex ecological interactions such as predation and competition play an important role in shaping the structure and function of marine communities. In fact, these processes can have greater impacts than those related to fishing. We assessed ecological interactions among economically important fishes in the Gulf of Alaska - a large marine ecosystem that has recently undergone considerable shifts in community composition. Specifically, we developed an index of predation for Walleye Pollock (Gadus chalcogrammus) to examine spatiotemporal changes in consumption, quantify portfolio effects, and better understand diversity-stability relationships within the demersal food web. We also evaluated the potential for competition between two important pollock predators, Arrowtooth Flounder (Atheresthes stomias) and Pacific Halibut (Hippoglossus stenolepis). We found highly variable predation intensity on Gulf of Alaska pollock. The combination of a single dominant predator and synchronous consumption dynamics indicated strong top-down control in the region. Spatial heterogeneity, however, may offset trophic instability at the basin scale. Assessments of resource partitioning provided little indication for competition between Arrowtooth Flounder and Pacific Halibut of similar lengths. Morphological differences between the two flatfish predators prompted an exploration into whether our conclusions about resource partitioning were dependent upon the size metric used. From this study, we found a relatively early onset of piscivory for Arrowtooth Flounder. Relationships between predator size and prey size also suggested gape limitation among Pacific Halibut sampled. Trophic niche separation was more pronounced for fishes with larger gapes, indicating greater potential for competition among smaller Arrowtooth Flounder and Pacific Halibut in Southeast Alaska. Reexamining basin-scale relationships between spatial and dietary overlap according to gape size would further elucidate the effects an increasing Arrowtooth Flounder population has had on changes in Pacific Halibut size-at-age. Results from this dissertation improve our understanding about the impacts of complex ecological interactions on population and community dynamics, and how those interactions may change in time, space, and under different environmental conditions.
• Ecological mechanisms and effectiveness of bioremediation in Alaska

What drives microbial community structure and function is a fundamental question of microbial ecology. Soil microbial communities have wide ranging metabolic capabilities, which include performing oxidation-reduction reactions responsible for cycling of nutrients and organic compounds and biodegradation of pollutants. One major determinant of microbial function in soils is vegetation type. Considering plants are diverse in chemical composition, they impact the quantity and quality of carbon and nutrients available to microbes through root turnover, root leachates, as well as by altering pH and soil microclimate (moisture, temperature). Rhizosphere interactions, in the form of phytoremediation, can be capitalized upon to provide a potentially cost effective method for detoxifying contaminated soils using plants and associated soil microorganisms. The remote locations and cold climate of Alaska provide unique challenges associated with phytoremediation such as finding effective plant species that can achieve successful site clean-up despite the extreme environmental conditions that includes minimal site management. Here we investigate the potential mechanisms and related effectiveness of microbial communities and native boreal vegetation associated with contaminant degradation and biogeochemical cycling. We examined three different soil systems to understand how dominant vegetation type, historical treatment and contamination shape the microbial community structure and functional potential. First, we used stable isotope probing to understand how microbial communities act in concert to biotransform the recalcitrant contaminants, polychlorinated biphenyls. Second, we sought to understand if dominant vegetation type controls microbial community structure and function either through direct impacts of plant root exudates and detritus or indirectly through the influence of plants on soil chemistry, composition, and structure. Finally, we conducted a forensic investigation of a petroleum contaminated site with no active site management for 15 years to assess the long-term effects of phytoremediation on soil petroleum concentrations, microbial community and vegetation colonization. The results of these experiments provide novel insights into the mechanisms of contaminant removal in boreal forest soils and the role of plants in ecosystem resilience to contamination, and demonstrates that phytoremediation using native and local plants can be an effective means to treat petroleum contaminated soils.
• The ecological niche of storm-petrels in the North Pacific and a global model of dimethylsulfide concentration

Ecological niche modeling techniques were used to create global, monthly predictions of sea surface dimethylsulfide (DMS) concentrations, and breeding season distribution of Leach's Storm-Petrel (Oceanodroma luncorhoa) and Fork-Tailed Storm-Petrel (O. furcata) in the North Pacific. This work represents the first attempt to model DMS concentrations on a global scale using ecological niche modeling, and the first models of Storm-Petrel distribution for the North Pacific. Storm-Petrels have been shown to be attracted to DMS, and it is therefore likely that a model of sea surface DMS concentration would help explain and predict Storm-Petrel distribution. We have successfully created the most accurate models of sea surface DMS concentrations that we are currently aware of with global correlation (r) values greater than 0.45. We also created Storm-Petrel models with area under the receiver operating characteristic curve (AUC) values of greater than 0.90. Using just DMS as a predictor variable we were also able to create models with AUC values upwards of 0.84. Future conservation efforts on pelagic seabird species may be dependent on models like the ones created here, and it is therefore important that these methods are improved upon to help seabird management on all scales (global, national, regional and local).
• Ecological studies of the benthic fauna in an arctic estuary

Distributions and abundances of benthic fauna are described for the nearshore Beaufort Sea adjacent to the mouth of the Colville River. Harrison Bay, Simpson Lagoon, and the shallow waters seaward of the barrier islands were sampled with a small bottom trawl and grab during the late summer of 1971. This survey was part of a larger effort by the University of Alaska to obtain baseline information prior to oil exploration and development. Forty-seven species, dominated numerically by Crustacea, Hollusca, and Polychaeta were studied from a collection of 86 samples. The isopod, Mesidotea entonon, and the mysid, Mysis oculata were common to all areas examined. Standing stocks of both were significantly higher (P<0.05) seaward of the lagoons. The spatial distribution of infauna clearly reflected the influence of the seasonal zone of bottom-fast ice. The biology, life history, and production of selected species are described, and relationships between environmental factors discussed as related to understanding this nearshore community.
• An ecological study of butter-clam (Saxidomus giganteus) toxicity in southeast Alaska

Butter clams (Saxidomus giganteus) at South and North porpoise Islands and Pleasant Island, Southeast Alaska, were occasionally found to accumulate significant amounts (higher than the maximum human tolerance) of paralytic shellfish poison (PSP) at any season of the year, and to occasionally lose or regain PSP rapidly between two samplings. The fluctuations of toxicity levels were not similar at all stations and no consistent patterns were Observed. The toxicity of only 19 out of 53 samples collected at three high-toxicity stations exceeded the maximum human tolerance level for PSP (1200 MU), and clam samples taken from moderate and low-toxicity stations never exceeded this level. Neither phytoplankton populations nor hydrographic parameters had a consistently significant correlation with toxicity levels; however, fluctuations of phytoplankton numbers demonstrated an inverse relationship with fluctuations of inorganic nutrient concentrations. Dinoflagellate maxima tended to occur at relatively low salinity (22% - 29%) and relatively high temperatures (7°C - 16°C), whereas the diatom numbers did not significantly correlate with salinity or temperature. The three high-toxicity stations were all within Icy Passage; fluctuations of phytoplankton populations and the hydrographic conditions at these stations were similar, yet the fluctuations of toxicity levels were quite dissimilar. A number of possible sources may be responsible for the butter-clam toxicity in Southeast Alaska. However, more studies are needed to define the cause of the butter-clam poisoning problem in Southeast Alaska.

• Ecology and energetics of early life stages of walleye pollock in the eastern Bering Sea: the role of spatial variability across climatic regimes

Understanding mechanisms behind variability in early life survival of marine fishes can improve predictive capabilities for recruitment success under changing climate conditions. Ecosystem changes in response to climate variability in the eastern Bering Sea affect commercial species including walleye pollock (Theragra chalcogramma), which represent an ecologically important component of the ecosystem and support the largest commercial fishery in the United States. The goal of my dissertation was to better understand spatial and temporal dynamics in the ecology of early life stages of walleye pollock in the eastern Bering Sea through: (1) an examination of shifts in larval fish community composition in response to environmental variability across both warm and cold conditions; (2) a quantification of the seasonal progression in energy content of age-0 walleye pollock which provides critical information for predicting overwinter survival and recruitment to age-1 because age-0 walleye pollock rely on sufficient energy reserves to survive their first winter; and (3) a modeling approach to better understand the role of prey quality, prey composition, and water temperature on spatial and temporal patterns of juvenile walleye pollock growth with implications for year-class survival and recruitment success. In the community analysis, I identified a strong cross-shelf gradient delineating slope and shelf assemblages, an influence of water masses from the Gulf of Alaska on species composition, and the importance of nearshore areas for larval fish. Species assemblages differed between warm and cold periods, and larval abundances, including that of walleye pollock, were generally greater in warm years. I identified different energy allocation strategies indicating that distinct ontogenetic stages face different survival constraints. Larval walleye pollock favored allocation to somatic growth, presumably to escape size-dependent predation, while juveniles allocated energy to lipid storage in late summer. Finally, I provide evidence that a spatial mismatch between juvenile walleye pollock and growth 'hot spots' in 2005 contributed to poor recruitment while a higher degree of overlap in 2010 resulted in improved recruitment. I highlight the importance of climate-driven spatial patterns in community structure, prey dynamics, and environmental conditions that influence the growth and survival of an important gadoid population in a sub-arctic marine ecosystem.
• 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.
• The ecology of age-1 copper rockfish (Sebastes caurinus) in vegetated habitats of Sitka Sound, Alaska

Variables that may indicate habitat quality were measured to assess the relative value of shallow subtidal vegetated habitats to age-1 copper rockfish (Sebastes caurinus). All habitats studied appeared beneficial to fish with respect to the particular variable measured. Relative growth rate was significantly higher in kelp than in other habitats while energy content was highest in eelgrass. Though fish in eelgrass had lower growth rates, they were significantly larger, and had high densities. Mixed kelp and eelgrass habitat was suboptimal with respect to growth and energy content but also had high densities. Fish in mixed habitat moved the least both within and to other habitats while the opposite occurred in eelgrass. Diets were similar for fish in kelp and eelgrass habitats and daily ration did not differ significantly between habitats. Thus, observed differences in the variables measured were not related to food but may instead be dependent on non-exploitative interactions.
• Ecology of birch litter decomposition and forest floor processes in the Alaskan taiga

Our view of an ecological process is influenced by the scale of our hypotheses and experiments. The forest floor can be examined as a system, where processes that affect ecosystem carbon and nutrient cycling are controlled by macroscale variables (seasonal climatic changes), which in turn affect microscale controls over microbial activity. In the forest floor of Alaskan taiga, annual layers of Equisetum (horsetail) litter demarcate cohorts of birch litter. We collected samples of the forest floor monthly during September 1992, and in June-September 1993. Forest floor material was separated into each of the three most recent litter cohorts, plus the Oe layer, and the Oa layer. Overall, respiration potential decreased with depth of litter (litter age), but showed no change over time. Nitrogen mineralization potential increased with depth, and fluctuated over time. Microbial biomass did not vary with depth, but did increase greatly in September in conjunction with increased litter moisture. Litter C:N ratio decreased with time and varied with depth according to the year-to-year variation in litter quality. Our hypothesis that microbial activity on a particular litter cohort is a function of the litter quality, the vertical position of the litter in the forest floor, and the timing of the observation within seasonal macroclimatic cycles was supported. The distribution of some taxa of soil fauna correlated with depth. In these cases, the fauna were likely constrained mostly by differences in the microclimate of the forest floor strata. Other soil fauna varied over time, likely in response to differences in the microbial community. Yet other faunal distributions showed an interaction between depth and time, apparently responding to a combination of changes in microclimate and changes in food availability. The creatures that live in water pores may also have responded to an increase in habitat space as the top-most litter strata became wetter. "Cascading" microcosms containing material from these forest floor strata showed a temporary suppression of respiration by leachates from the newer litter on underlying forest floor material. Traditional litterbag techniques were also used to show changes in nitrogen that indicate winter microbial activity.
• The ecology of eulachon (Thaleichthys pacificus) in Twentymile river, Alaska

The ecology of eulachon (Thaleichthys pacificus) was studied at Twentymile River, a tributory of Turnagain Arm located in southcentral Alaska. In 2000 and 2001, we investigated the environmental factors associated with the migration of adult eulachon and downstream drift of larval eulachon. We assessed run timing, freshwater duration, length, weight, age, presence or absence of teeth, fecundity, and gear selectivity for dip and gill nets. Catch per unit effort of migrating adult fish were correlated with water temperature, tide height, river discharge, light intensity, and the density of bald eagles (Haliaeetus leucocephalus). Water temperature, river discharge, tide height, and light intensity were related to downstream drift intensity of larvae. Radio telemetry was used successfully to study the migratrion movements of adult eulachon. Clusters of the upstream limits of migration identified four common spawning areas in both years.
• Ecology Of Juvenile Pink Salmon In The North Gulf Of Alaska And Prince William Sound

Increased production of salmon in Alaska has been accompanied by a decrease in average body size and decreased wild stocks, indicating a possible density-dependent response to increases in salmon populations and hatchery releases. Pink salmon have a short two-year life cycle and most post-hatch mortality is thought to occur during their first months at sea; therefore, processes in the early marine residence period may determine abundance. Geographic and seasonal patterns in distribution, growth, and condition of juvenile pink salmon during their first months at sea were examined in Chapter 1. The migration of pink salmon from Prince William Sound (PWS) occurred over several months. Fish lengths, weights, and energy contents varied geographically and seasonally. Pink salmon energy content was highest on the Gulf of Alaska (GOA) shelf in July and August and lowest in PWS in July, indicating that growth conditions were better on the GOA shelf. Spatial and temporal variation in growth and condition is indicative of disparate feeding opportunities for juvenile pink salmon. An unusual aspect of this study was the concurrent collection of zooplankton and fish in PWS and on the GOA shelf. Geographic and seasonal changes in juvenile pink salmon diets were examined during their first six months at sea in Chapter 2. Pink salmon diets varied geographically and seasonally, and prey size increased as fish grew. A unique opportunity existed to compare the energy content of thermally marked hatchery pink salmon to their wild counterparts in PWS (Chapter 3). Fish condition varied geographically, however, there were no differences among hatchery groups and/or wild pink salmon at any one location. This indicates that fish were staying together as a group. In Chapter 4, pink salmon consumption was estimated to represent a small fraction of the production but potentially a large proportion of the available standing stock of zooplankton in PWS. Geographic variations in fish condition, diet, and zooplankton densities were observed in this study. This supports the hypothesis that local processes, including food depletion and/or zooplankton availability are important to juvenile pink salmon.
• Ecology of mountain sheep: effects of mining and precipitation

We examined effects of mining on mountain sheep (Ovis canadensis nelsoni) in California. Size of home range, forage quality, and diet did not differ between populations in mined and nonmined areas. During summer, we observed the greatest disparity in time spent feeding and diet quality. Because of their dependence on a spring adjacent to the mine, sheep may have spent more time vigilant, and less time feeding. Reducing mining during summer may benefit sheep. We also compared ecology of two female mountain sheep populations from different areas (xeric vs. mesic) in the Mojave Desert. The more xeric Panamint Range was typified by more bare ground, less shrubs, less grass, and larger home ranges than at Old Dad Peak. Females from Old Dad foraged on grasses, whereas those from the Panamints consumed shrubs. We concluded that sheep from the Panamints required larger home ranges because of lower-quantity and quality of forage.
• 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.
• Ecology Of Reindeer On Hagemeister Island, Alaska

The objective of this study was to investigate and characterize the factors driving the Hagemeister Island reindeer population. A total of 144 reindeer were introduced to Hagemeister Island in 1965 and 1967. The herd initially increased in size to about 1,000 head and then fluctuated around 800 animals. In 1991-1992, a moderate winter die-off of primarily adult bulls ($>$90%) occurred. Adverse snow conditions and poor post rut conditions of bulls appeared to have facilitated the die-off. No conclusive evidence was found that the herd experienced effects of density-dependent food limitation despite poor winter lichen range. In 1993, conception was documented in calves and overall pregnancy rate was approximately 70%. Body size and condition was comparable to other arctic island reindeer herds. This suggests that reindeer on Hagemeister Island do not solely depend on lichen during winter but utilize other forages. <p>