Differences in the chemical composition of calcified structures can be used to reveal natal origins, connectivity, metapopulation structure, and reconstruct the environmental history or movement patterns of many marine organisms. Sharks, skates, and rays (elasmobranchs) lack the calcified structures, known as otoliths, that are typically used for geochemical studies of...
Forests in the Pacific Northwest receive very little nitrogen through atmospheric deposition and thus studying the nitrogen cycle in this region can provide insights into how the unpolluted nitrogen cycle functions. I examined the fate of organic nitrogen versus inorganic nitrogen and the effect of tamlins on N retention by...
I used current water management practices in central and eastern Oregon and Washington as natural experiments to quantify the effects of irrigation water withdrawals on macroinvertebrate community structure and life history strategies. Reduced discharge had direct (e.g. decreased velocity and wetted habitat) and indirect (e.g. increased conductivity and temperature) effects...
The forest alpine tundra ecotone (FTE, also known as alpine treeline or subalpine parkland), is a conspicuous feature of mountain landscapes throughout the world. Climate change-driven increases in temperature are believed to result in FTE movement and tree invasion of subalpine meadows, which have been documented throughout the Northern Hemisphere...
We are at risk of losing the sagebrush steppe in the floristic Great Basin to the invasion of Bromus tectorum L., cheatgrass. The floristic Great Basin includes the Central Basin and Range, the Northern Basin and Range, and the Snake River Plain. The Great Basin receives most of its precipitation...
Human alteration of natural landscapes leads to biodiversity loss, often from a combination of area effects and fragmentation effects. Smaller habitat patches support fewer species than large ones and incur additional consequences from isolation. Efforts to preempt biodiversity loss from insular habitat fragments are complicated by individualistic species responses and...
The western United States has experienced large-scale degradation due to land use and land cover changes, invasion of annual grasses, and expansion of woody plants into grass and shrublands and the resultant altered fire regimes. These landscape-scale changes have coincided with declining mule deer (Odocoileus hemionus) populations, making habitat loss...
I compare the seasonal abundance variation, population dynamics, fecundity, egg hatching mechanism and success, and apostome ciliate parasites of the euphausiids Euphausia pac?fica and Thysanoessa spinfera from the Oregon coast, USA. Community structure and nearshore distributions were examined from bi-weekly oceanographic surveys (1970-1972). This region has a strong cross-shelf change...
Biological invasions threaten native biodiversity, alter ecosystem function, and are a major cause of economic losses across the planet. The most impactful invaders alter disturbance regimes and initiate state shifts to outside the historical range of variability of the ecosystem. Concern for ecological and economic losses has prompted a rapid...
Changes in ocean conditions influenced by climatic fluctuations have lead to changes in individual species distributions, which alter the diversity, communities and species interactions across marine ecosystems worldwide. Assessing the species composition and identifying regions and habitats that can safeguard the persistence of biota are critically important. In this dissertation,...