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Drivers And Dynamics Of Phytoplankton Communities And Harmful Algal Blooms In Mountain Lakes, Lara Stephanie Jansen

Dissertations and Theses

Harmful cyanobacterial blooms (cyanoHABs) are a complex and widespread disturbance in freshwater water bodies, impacting water quality for wildlife and human populations. While cyanobacteria often bloom in warm lakes impacted by human development like agriculture, blooms are increasingly reported in cooler waters with limited development in the surrounding watershed. As much of cyanoHAB research has focused on lakes in highly developed watersheds, the understanding of factors leading to cyanobacteria dominance and blooms in the absence of major development remains limited. Mountain lakes can serve as ideal systems to study bloom-forming cyanobacteria in watersheds with minimal development. In addition, mountain lakes …

Fungal Endophytes In A Seed-Free Host: New Species That Demonstrate Unique Community Dynamics, Brett Steven Younginger

Dissertations and Theses

Fungal endophytes are highly diverse, cryptic plant endosymbionts that form asymptomatic infections within host tissue. They represent a large fraction of the millions of undescribed fungal taxa on our planet with some demonstrating mutualistic benefits to their hosts including herbivore and pathogen defense and abiotic stress tolerance. Other endophytes are latent saprotrophs or pathogens, awaiting host plant senescence to begin alternative stages of their life cycles. Most, however, are likely plant commensals with no observable benefits to their hosts while under study. Yet, when considering the context-dependence that may determine plant resistance to pathogen attack, the consortium of endophytes present …

Externally-Expressed Fluorescence Across Sexes, Life Stages, And Species Of Spiders, Erin Brandt

Dissertations and Theses

Although all spiders possess fluorophores in their hemolymph, the expression of external fluorescence is much more restricted. The purpose of this study was to evaluate differences in externally-expressed fluorescence between sexes, life stages, and species of spiders. To approach this question, we developed novel instrumentation to capture fluorescence with photographs of our specimens. We paired these fluorescence measurements with spectrometer measurements to attempt to determine the role that fluorescence plays in the overall coloration in spiders. The study was divided into four sections. First, we examined how fluorescence varies in sexes and life stages in Misumena vatia, an ambush predator …

The Effect Of The Study Region On Gis Models Of Species Geographic Distributions And Estimates Of Niche Evolution; Preliminary Tests With Montane Rodents (Genus Nephelomys) In Venezuela, Ali Raza

Dissertations and Theses

Various niche-based techniques exist to model a species' potential geographic distribution in a Geographic Information Systems (GIS) framework. These models compare the environmental conditions of localities of a species' occurrence versus those of the overall study region. In addition to uses in areas such as macroecology and conservation biology, this approach has been applied recently to studies of niche evolution and historical biogeography. Definition of the study region is critical for all of these applications but has not been addressed previously. Here, I examine the effect of changes in the extent of the study region on potential distribution models of …

Zoonotic Disease Emergence : A Study Of Host-Pathogen-Ecosystem Dynamics, Laurie Jeanne Dizney

Dissertations and Theses

A growing body of work demonstrates that loss of biodiversity negatively impacts ecosystem functions. One function, or service, that biodiverse ecosystems provide is suppression of zoonotic diseases, which are defined as diseases carried by wildlife hosts that can spill over into human populations. Ebola, SARS, West Nile virus, Hantavirus, Avian Influenza and Lyme disease are just a few of the recently emerging zoonotic diseases. Disease suppression has been shown for Lyme disease by the dilution effect, whereby increasing species diversity decreases disease prevalence in the host populations. But does a dilution effect apply to other disease systems? To test this …

The Impacts Of The Introduced European Green Crab, Carcinus Maenas, On Selected Bivalves And Meiofaunal Communities, Zasha A. Bassett

Dissertations and Theses

This thesis examines the potential impact of the invasive green crab, Carcinus maenas, in Yaquina Bay, Oregon. I sampled the current extent of crab colonization in the intertidal zone of Yaquina Bay using a standardized trapping regimen in selected intertidal sites in August and September 1999. I also evaluated the potential impacts of C. maenas on the commercially important bivalve, Crassotrea gigas. Carcinus' preferred size ranges of C. gigas and other species were experimentally determined. Additionally, Carcinus species preference for C. gigas was examined in relation to two common bivalves, Mytilus trossolus and Macoma nasuta. Experiments were also conducted to …

The Periphyton Community Of A Second Order Subalpine Stream Following Salmon Carcass Decomposition, Jonathan Micheal Honea

Dissertations and Theses

To protect and manage Pacific Northwest salmonid stocks, sound management programs must be developed that incorporate knowledge of the ecological processes critical to their survival. One such process is the nutrient dynamic in headwater spawning streams. It is essential that we understand the trophic relationships among the spawners, the I to 3 year-old juveniles, the invertebrates, and the primary producers in these streams.

The hypothesis that I tested is that photoautotrophic production increases due to the decomposition of salmon carcasses. Increased primary production would stimulate the production of invertebrates which are an important food resource of juvenile salmonid species. The …

Phytoplankton In Mt. St. Helens Lakes, Washington, Cynthia Fay Baker

Dissertations and Theses

Phytoplankton communities in fifteen lakes in the Mt. St. Helens area were surveyed to assess the abundance and species present. Eleven of the lakes were inside the blast zone of the 1980 eruption and four were located outside the blast zone as a comparison. The hypothesis is that lakes will cluster together based on the algal species present and that some algae will be correlated with certain environmental conditions. A cluster analysis was performed to determine if the lakes would group together based on algal abundance. There did not appear to be any distinct clustering among the study lakes, but …

Thermal Ecology And Movement In The Leopard Lizard, Gambelia Wislizeni, Baird And Girard, Marvin Lynn Abts

Dissertations and Theses

Thermal ecology and movement of the Leopard Lizard, G. wistizeniwere studied at Frog Spring, adjacent to the Alvord Desert, and at various locations throughout the Alvord Basin. Seasonal activity is known to occur from early May to mid-October, but abundance. gradually decreases after late July. During favorable late spring, and summer weather lizards exhibit a bimodal pattern of diel activity with some activity occurring at all hours of the day between 0600 and 1800 H. At other times activity was unimodal. Emergence was apparently largely temperature dependent and did not occur until sand temperature approximated 21°C. Retreat appeared to …

Interactions In The Frequencies Of Electric Organ Discharge By Eigenmannia Virescens (Sternopygidae, Pisces) During Social Behavior, Philip Gaddis

Dissertations and Theses

The extent to which individuals of Eigenmannia virescens modulate their electric organ discharge frequencies to accommodate the frequencies of others of the same species during social interactions was investigated. Recordings of the fish's discharge frequencies, taken with Tektronix 3L5 and 5L4N spectrum analyzers, showed that, although movements of up to 60 Hz in a day may be made, the frequency movements would be made more or less synchronously by all fish in the group. An apparent preference for, and a tendency of the fish to follow one another in frequency, at frequency ratios of 2:3 (a musical fifth), 3:4 (fourth), …