Soil food webs process the majority of terrestrial carbon, and influence overall ecosystem function. A primary distinction among soil food webs is based on fungal versus bacterial pathways of decomposition; these lead to fundamentally different soil function, and are expected to differ in dominance between meadows and forests. This assumption...
In the Coast Range of western Oregon, some natural resource managers are converting red alder-dominated riparian areas to conifers to increase the future source of in-stream large wood for salmonid habitat. However, studies in Alaska have shown red alder-dominated riparian areas support greater invertebrate biomass compared to conifer-dominated areas. In...
The Northern California Current (NCC) ecosystem exhibits extreme seasonal, interannual and interdecadal shifts in the abiotic environment and shifts in primary and higher production. This variability is also apparent in the spatial structure of the ecosystem with nearshore-shelf waters (<150 m isobath) being highly productive and having a different community...
Variable ocean conditions can greatly impact lower trophic level prey assemblages in marine ecosystems, with effects propagating up to higher trophic levels. Our goal was to better understand how varying ocean conditions influence diets and niche overlap among a suite of low- to mid trophic level predators. We studied the...
Riparian areas are eco-tones where aquatically- and terrestrially-derived insect biomass is exchanged between habitats, presenting consumers with new sources of energy, and resulting in a reciprocal subsidy. The relative contribution of energy exchange and the
resulting impacts on vertebrate riparian consumers, such as fish or birds, remains poorly understood. We...
Studies on elemental and energy transfer in lower trophic levels in
the marine environment were initiated in July 1962 after receipt of AEC
contract AT(45-1)1751. It should be pointed out that this report covers
only a six-month period, because for bookkeeping purposes the contract
was made retroactive to 1 April...
Phytoplankton and microzooplankton comprise the base and the first link of the marine food web, respectively. These microbes are key drivers of marine carbon and nutrient cycles. Phytoplankton convert atmospheric CO₂ into organic carbon, and microzooplankton consume phytoplankton, packaging phytoplankton carbon into particulate forms that have a variety of fates:...
Calow (1983) realized that differences between parasites and their free-living
relatives can be explained by the differences in nutrient richness. I
propose a model that is based on Calow's idea which identifies the relative
position of different trophic strategies (e.g. predation, grazing, parasitism and
others) based on (1) the differences...
"During the four meetings of the consumer modeling committee, discussion centered on the formation of systems models and the
problems they will pose for researchers concerned with consumer populations. Two coarse models were developed from these discussions, a compartment model (Figure 1) and a process model (Figure 2). The
compartments...
"We have developed graphical and logical models for explaining the production of a consumer on the basis of the capacity of an ecosystem to produce that consumer (the productivity of the system for that consumer), on the basis of the biomass of the consumer, and on the basis of the...
Isotope and stomach content data from piscivorous reservoir fishes collected from Hills Creek (isotopes; 43°40′16″N 122°25′33″W) and Lookout Point (isotopes and stomach contents; 43°53′48″N 122°43′34″W) reservoirs located on the Middle Fork Willamette River, Oregon. Additional details can be found in the related publication.
Isotope sampling was conducted under OSU Institutional...
The relationships between inorganic nutrient supply and the first two trophic levels have long been understood in a very approximate manner but the dynamics of such a system cannot be explored adequately by simple
arithmetic when nonlinear relationships exist. An exploration of such a
system was accomplished by the use...
Humans are increasing the scale and frequency of many natural disturbances, as well as adding novel disturbances to ecosystems. This thesis uses the arthropod community as a metric to examine the multi-trophic responses to disturbances in California grasslands. Chapter 2 explores how the long-term exclusion of native vertebrate herbivores has...
The effects of harvesting Pacific hake (Merluccius productus)
were examined with a multi-species numerical model composed of
seven logistic growth equations coupled by a food web. The
food web was composed of: California sea lions (Zalophus
californianus), hake, sablefish (Anaplopoma fimbria), spiny
dogfish (Squalus acanthias), a generic rockfish species
(Sebastes...
Marine systems undergo changes in community composition over time as a result of a variety of environmental and anthropogenic factors. Understanding these community changes and the factors that drive them is critical for ecosystem management of marine resources. The Gulf of Alaska (GOA) is a large marine ecosystem that includes...
Dislodged macroalgae and seagrasses, also known as marine wrack, frequently wash into coastal ecosystems from the ocean and are potentially important ecological resources for biological communities. These!nutrient and organic matter subsidies may be especially important on sandy beaches, where little in situ primary productivity exists for higher trophic levels. To...
I studied spring food habits, focusing on cambium-feeding, of black bears (Ui-gus americanus) in the Central Coast Ranges of Oregon (1987-90) by comparing an area with high levels of timber damage caused by bears (north area) with an adjacent area of low levels of bear damage (south area). I also...
Understanding food webs is fundamental in conserving endangered species and maintaining healthy ecosystem function, particularly in desert spring systems. We identified dominant energy sources in the Muddy River Warm Springs area, Clark County, NV using carbon and nitrogen natural abundance stable isotope analyses. We examined isotopic signatures of specific macroinvertebrate...
The quality and availability of forage fishes and invertebrates can affect the behavior and productivity of predators that rely on these resources. This study measures the proximate composition of forage fishes and invertebrates from the southeastern Bering Sea to estimate prey energy density (quality) using a method that is ecologically...
This thesis presents two related studies on the methodology for creating, and
subsequently analyzing, an inverse food web model of an intertidal seagrass bed. The first study (Chapter 2) describes, for the first time in the literature, a method for incorporating isotopic information gained from Bayesian mixing models into an...
Although it is generally assumed that the intensifying abiotic environment is the primary effect of drought on aquatic organisms, drought-induced top predator extinctions may be an important underlying mechanism. I used manipulative experiments to disentangle the impacts of drying and top predator extinctions on arid-land aquatic invertebrate communities. I then...
According to general top-down trophic theory, in the presence of carnivores, herbivore behavior and/or densities could change and result in an overall decrease in herbivory on plant communities. In this dissertation, I examined the potential relationship between gray wolf (Canis lupus) presence and absence on elk (Cervus elaphus) herbivory of...
In salmon-rich, northern coastal environments brown bears can occur at high densities and exert wide-ranging effects on ecosystem processes. Bear consumption of seasonally available fruit may provide important seed dispersal services to plants, and by extension, influence the ecology of seed consumers such as small mammals. In this study, we...
Reintroduction of wolves to Yellowstone National Park (YNP) in 1995-96 provided a rare opportunity to observe the response of an ecosystem to the return of a top predator, including possible reversal of decades of decline of aspen, cottonwood, and tall willows suppressed by intensive herbivory on elk winter ranges. To...
Mercury (Hg) contamination is a global conservation threat to freshwater ecosystems, detected in even the protected lakes of Olympic National Park (Washington, USA). Although considered some of the most remote and pristine US ecosystems, these lakes are currently subject to multiple environmental stressors, including climate change and fish introductions; adding...
Macrobenthos populations of the IBP lakes were sampled during October and November of 1972. Analyses of the samples revealed dominance of chrinomids and oligochaetes in both littoral and profundal regions for at least this time of year. Due to sampling difficulties the oligochaete material was not used for chemical analyses....
Thiamine (vitamin B₁) is required by all living organisms for carbohydrate metabolism and synthesis of amino acids. Thiamine deficiency is responsible for several related classes of early life stage mortality disorders in salmonines, including Thiamine Deficiency Complex (TDC) in the Laurentian Great Lakes, Cayuga Syndrome in the Finger Lakes, and...
Bullfrogs were introduced into Oregon in the early 1900s and have become widespread members of many wetland communities. Little is known of their ecology outside their native range, although they may play a role in the current declines observed in native herpetofauna. I analyzed the diets of 401 bullfrogs from...
Coastal cutthroat trout (Oncorhynchus clarkii clarkii) and cottids (Cottus spp) commonly co-occur in headwater streams in western Oregon. Little is known about the comparative trophic ecology of these species or how they respond to seasonal scarcity of resources. In this study I evaluated the seasonal variability in diets and consumption...
Ultraviolet-B radiation (UVB) is an abiotic stressor in both terrestrial and aquatic systems. The stratospheric ozone layer, depleted due to anthropogenic activities and the cause of elevated UVB at earth's surface over the last four decades, is predicted to recover by 2065. However, UVB levels in aquatic systems may continue...
Concentrations of selenium (Se), manganese (Mn), zinc (Zn), cadmium (Cd), lead (Pb) and arsenic (As) were measured in the water column, sediment and biota, in conjunction with selected physicochemical data, from representative wetland types at a mining site within Salt Lake County, Utah, USA. The selected field sites included Oolitic...
The federally threatened northern spotted owl (Strix occidentalis caurina) is the focus of intensive conservation efforts that have led to much forested land being reserved as habitat for the owl and associated wildlife species throughout the Pacific Northwest of the United States. Recently, however, a relatively new threat to spotted...
Mule deer (Odocoileus hemionus hemionus) and Rocky Mountain elk (Cervus canadensis nelsoni; hereafter elk) populations in northeast Oregon have declined in the past 10 to 20 years. Concurrent with these declines, cougar (Puma concolor) populations have apparently increased, leading to speculation that predation by cougars may be responsible for declining...
This thesis merges the fields of Ecology and Anthropology by applying Habitat Suitability Modeling to the relationship between people and plants in the Pacific Northwest. In it, I create and optimize two Maxent habitat suitability models for camas (Camassia spp.) in Oregon. The first model describes the physical environment of...
A causative factor in declining greater sage-grouse (Centrocercus urophasianus)
populations is reduced annual recruitment due to poor habitat quality. Sage-grouse
population decline is concurrent with a decline in the extent and quality of the
sagebrush (Artemisia sp.) biome. However, current research has shown a positive
relationship between sage-grouse brood and...
Populations of organisms are influenced by both top-down (predator driven) and bottom-up (environment or resource driven) effects. Seabird research has largely focused on bottom-up factors influencing reproduction, with little emphasis on top-down. Our goal was to better understand top-down impacts on colonial nesting seabirds over a range of spatio-temporal scales....
Food webs consist of a combination of bottom-up (resource-driven) and top-down (predator-driven) effects. The strength of these effects depends on the context in which they occur. I investigated food web (trophic) relationships between wolf (Canis lupus) predation, elk (Cervus elaphus) herbivory, aspen (Populus tremuloides Michaux) recruitment, and fire. The study...
The marine environment is under increasing pressure from human activities worldwide, particularly in coastal waters, creating a need to better understand fine-scale distributions of highly mobile species that occur in the area, as they are frequently most threatened. Harbor porpoise (Phocoena phocoena) occur frequently in Oregon’s nearshore habitat, but due...
The importance of pollinators in native and managed landscapes is well known, and recent interest is directed towards investigating the role of native bees as providers of pollination ecosystem services. Uncertainty about bee populations at global and local scales has prompted research and general interest in conservation of bee diversity....
Wetland restoration success in attaining wildlife conservation goals can be confounded by the presence of multiple biological invaders. Wetland management activities typically target invasive plants, but bottom-up responses of higher trophic levels in novel communities are difficult to predict. We surveyed plant and amphibian assemblages at 26 sites enrolled in...