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Life Sciences

Theses/Dissertations

1996

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Full-Text Articles in Physical Sciences and Mathematics

The Real Cost Of Beef: A Monetary Assessment Of The Environmental Degradation Caused By Beef Production, Carolyn Babcock Jul 1996

The Real Cost Of Beef: A Monetary Assessment Of The Environmental Degradation Caused By Beef Production, Carolyn Babcock

UNLV Theses, Dissertations, Professional Papers, and Capstones

The environmental degradation caused by beef production is severe. The current literature assesses the ecological damage, but falls short of assigning a per pound dollar amount to reflect the real cost of beef. In the United States, most of the environmental focus has been centered around the use of public lands for grazing and the grazing fee the government considers appropriate. The fee covers the maintenance of the grazing program, which includes maintenance of the actual land. This paper will concentrate on beef-related environmental degradation and select specific damage for monetary valuation.


Comparison Of Positive Screening And Confimatory Results From Federally Mandated Drug Testing Of Urine, Mary M. Stuck Jul 1996

Comparison Of Positive Screening And Confimatory Results From Federally Mandated Drug Testing Of Urine, Mary M. Stuck

Community & Environmental Health Theses & Dissertations

The purpose of this study was to analyze the accuracy of FDA approved immunoassays for the detection of drug positive urine samples.

Federal civilian employees are tested under the strict protocol of the Department of Health and Human Services mandatory guidelines for federal workplace drug testing programs. The guidelines provide for a two instrument testing protocol for the analysis of urine samples. The first is an FDA approved immunoassay. Samples which test positive on this screening immunoassay are then submitted for confirmatory testing with the "gold standard" gas chromatography/mass spectrometry.

Agency monthly drug testing summaries, required under the DHHS guidelines …


An Avian Botulism Epizootic Affecting A Nesting Site Population Of Presbyornis : On A Carbonate Mudflat Shoreline Of Eocene Fossil Lake, V. Leroy Leggitt Jun 1996

An Avian Botulism Epizootic Affecting A Nesting Site Population Of Presbyornis : On A Carbonate Mudflat Shoreline Of Eocene Fossil Lake, V. Leroy Leggitt

Loma Linda University Electronic Theses, Dissertations & Projects

The shorebird-duck mosaic bird, Presbyornis, is best known from the Eocene Green River Formation where it often occurs in local monospecific bonebeds, suggestive of mass mortality events. The sedimentology, paleontology, taphonomy, XRD mineralogy, and the carbonate stable isotope signature (δ18O) of one of these bonebeds was studied on the southern margin of Eocene Fossil Lake.

A series of 408 standardized radiographs were used to construct the first large scale radiograph aided taphonomic map of a vertebrate fossil quarry (3,874 bones were recorded in 11.5 m2). A small group of 100 bones (including a complete skull …


Isolation From Soil Microorganisms That Are Inhibitory To Wheat Seeding Pathogens, Kynita Wilson-Humphrey May 1996

Isolation From Soil Microorganisms That Are Inhibitory To Wheat Seeding Pathogens, Kynita Wilson-Humphrey

McCabe Thesis Collection

Many diseases caused by bacteria, viruses, or fungi are responsible for the ruin of a great number of crops annually. At present, many of these crops are being treated for diseases by synthetic or man-made chemicals. Some of the chemicals have been proved to have adverse effects on the environment, including humans and animals. Very few non-chemical means are available to farmers at this time to control these pathogens. This is due to the fact that many of the means of control have little effect against the pathogens or diseases. This research attempts to isolate microorganisms from the soil which …


An Ecological History Of Tintic Valley, Juab County, Utah, Jeffrey A. Creque May 1996

An Ecological History Of Tintic Valley, Juab County, Utah, Jeffrey A. Creque

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

This work was a case study of historical ecological change in Tintic Valley, Juab County, Utah, an area historically impacted by mining and ranching activities common to much of the American West. The temporal framework for the study was approximately 120 years, the period of direct Euroamerican influence. In recognition of the ecological implications of cultural change, however, the impacts of prehistoric and protohistoric human activity on study area landscape patterns and processes were also explicitly addressed.

The study included a narrative description of historic land uses and ecological change in Tintic Valley, and examined the changes in landscape patterns …


A Survey Of Employees Of The United States Department Of Agriculture's Animal Damage Control Program, Susan A. Schroeder May 1996

A Survey Of Employees Of The United States Department Of Agriculture's Animal Damage Control Program, Susan A. Schroeder

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

This study examined the attitudes of employees of the United States Department of Agriculture's Animal Damage Control (ADC) Program. This research examined ADC employees' attitudes about wildlife, the ADC program and ADC employment, wildlife damage management methods, euthanasia and the killing process, and the role of various public and private groups on ADC policy. This study also applied the theory of organizational capture to the ADC program to test its utility in explaining the attitudes and behaviors of employees. Results were based on a survey of ADC employees conducted in January 1995.

Survey responses were analyzed to explore associations between …


The Influence Of Forest Fragmentation And Landscape Pattern On American Martens And Their Prey, Christina D. Hargis May 1996

The Influence Of Forest Fragmentation And Landscape Pattern On American Martens And Their Prey, Christina D. Hargis

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Habitat fragmentation occurs when large tracts of an orginal habitat are replaced by smaller patches of two or more habitat types, largely through human activities. I studied the behavior of six measures of landscape pattern that seemed appropriate for quantifying fragmentation, and used these measures to investigate the effects of forest fragmentation on American martens (Martes americana) and their prey. The measures I selected were edge density, contagion, mean nearest neighbor distance between patches, mean proximity index, perimeter-area fractal dimension, and mass fractal dimension. To test the behavior of these measures with a variety of landscape patterns, I …


Second Growth Forest As Potential Marten Habitat In Western Newfoundland: An Examination Of Forest Habitat Structure And Microtine Abundance, Brian R. Sturtevant May 1996

Second Growth Forest As Potential Marten Habitat In Western Newfoundland: An Examination Of Forest Habitat Structure And Microtine Abundance, Brian R. Sturtevant

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The American marten (Martes americana) is associated with large tracts of relatively undisturbed, mature coniferous forests. I examined coarse woody debris (CWD) structure and small mammal abundance with respect to forest age and stem structure within second-growth forests, in comparison with old-growth stands in western Newfoundland. Results suggest that a critical change in marten habitat quality may occur at stand senescence, due to decreased tree competition, more complex subcanopy structure, and increased meadow vole (Microtus pennsylvanicus) abundance.

Analysis of stem structure within a chronosequence of 19 second-growth stands indicated high intertree competition, with dense canopy closure …


Habitat Selection And Movement Of A Stream-Resident Salmonid In A Regulated River And Tests Of Four Bioenergetic Optimization Models, Mark D. Bowen May 1996

Habitat Selection And Movement Of A Stream-Resident Salmonid In A Regulated River And Tests Of Four Bioenergetic Optimization Models, Mark D. Bowen

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

A bioenergetics model was constructed for stream-resident drift-feeding salmonids. Model predictions of surplus power (energy available per unit time for growth and reproduction) were not statistically distinguishable from observations of surplus power in three laboratory studies. Of 40 experimental trials in these three studies, the model correctly predicted surplus power in 39 cases (p < 0.05).

I collected observations of rainbow trout (Oncorhynchus mykiss) focal velocity and physical habitat availability in the Green River of northeastern Utah, USA (1988-1990). In the winter of 1988, Flaming Gorge Dam generated hydropower and delivered an lJDStable discharge regime with a higher mean discharge …


Mule Deer Highway Mortality In Northeastern Utah: An Analysis Of Population-Level Impacts And A New Mitigative System, Mark E. Lehnert May 1996

Mule Deer Highway Mortality In Northeastern Utah: An Analysis Of Population-Level Impacts And A New Mitigative System, Mark E. Lehnert

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Rerouting highways to accommodate construction of the Jordanelle Reservoir in northeastern Utah caused a dramatic increase in vehicle collisions with mule deer (Odocoileus hemionus). I evaluated the effectiveness of a new system of highway crosswalk structures installed to reduce deer losses and preserve seasonal migrations. In addition, I constructed computer simulation models to investigate how highway mortality has impacted the Jordanelle deer population.

The crosswalk system restricted deer crossings to specific, well-marked areas along highways where motorists could anticipate them. Subsequent to installation, mortality declined 42.3% and 36.8% along a four-lane and two-lane highway, respectively. I was unable …


Livestock As Seed Disseminators For Reseeding Degraded Rangelands: The Role Of Dung In Gap Formation And Plant Establishment, Brian S. Auman May 1996

Livestock As Seed Disseminators For Reseeding Degraded Rangelands: The Role Of Dung In Gap Formation And Plant Establishment, Brian S. Auman

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Livestock (cattle and sheep) were examined as seed disseminators for reseeding degraded Intermountain rangelands. "Hycrest" crested wheatgrass [Agropyron desertorum (Fisch. ex Link) Schult. X A. cristatum (L.) Gaert.] seed was fed to yearling Holstein steers and Suffolk ewes. Dung was collected from each animal type and deposited on plots of high and low densities of an annual [cheatgrass (Bromus tectorum L.)] and perennial [squirreltail (Sitanion hystrix Nutt.)] grass species. The experiment evaluated the ability of the dung to suppress the resident vegetation, and the recruitment and establishment of Hycrest seedlings emerging from the dung.

Sheep dung had …


The Effect Of Salinity Level Upon The Yield, Root Growth, And Water Extraction Of Contrasting Rooting Subpopulations Of Alfalfa (Medicago Sativa) Under Conditions Of Zero Leaching, Laura A. Vincent May 1996

The Effect Of Salinity Level Upon The Yield, Root Growth, And Water Extraction Of Contrasting Rooting Subpopulations Of Alfalfa (Medicago Sativa) Under Conditions Of Zero Leaching, Laura A. Vincent

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

A major problem in irrigated agriculture in the Western U.S. is the gradual accumulation of salinity in the plant root zone. These nonuniformly saline soils contain increasing amounts of salinity with depth, and salt accumulation is accelerated in situations where leaching is minimized. Root growth and thus plant yield is limited in these soils due to decreased water uptake. We studied the root growth of two subpopulations of alfalfa differing in their ability to produce fibrous roots to determine if altering root morphology would increase plant yield and water extraction, in an irrigated saline soil.

Soil profiles for a control …


Evaluation Of The Delta Waterfowl Foundation's Adopt-A-Pothole Project, Daniel S. Vice May 1996

Evaluation Of The Delta Waterfowl Foundation's Adopt-A-Pothole Project, Daniel S. Vice

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The establishment of dense nesting cover (DNC) for breeding waterfowl is a common management practice on large blocks of former agricultural land. The Delta Waterfowl Foundation's Adopt-A-Pothole (AAP) program establishes DNC adjacent to small wetland complexes to increase waterfowl use and productivity. I evaluated waterfowl use and nesting success on AAP lease sites in southwestern Manitoba in 993- 94 and compared the relative amount and success of overwater and upland nesting by mallards using these sites.

Diving duck breeding pair densities were higher on treatment sites in both 1993 and 1994 (P = 0.02 and 0.02, respectively). Dabbling duck …


A Test Of An Alternate Calibration Matrix For Niosh Method 7300, Robert T. Vitek May 1996

A Test Of An Alternate Calibration Matrix For Niosh Method 7300, Robert T. Vitek

Community & Environmental Health Theses & Dissertations

The purpose of this study was to determine if the analytical results (when determining cadmium, lead, and zinc concentrations) for air sample filters prepared and analyzed according to N:OSH Method 7300, differ significantly, from those obtained when the instrument is calibrated using EPA Method 200.7 acid matrix standards. The null hypothesis was that no statistically significant difference, measured at the 95% confidence level, would exist between results obtained from the two calibration standards. Careful standard and sample preparation, the use of an internal standard, and the application of working standard and working internal standard correction factors served to isolate the …


Recruitment Of Blue Crab, Callinectes Sapidus, Postlarvae To The Back-Barrier Lagoons Of Virginia's Eastern Shore, Robert D. Brumbaugh Apr 1996

Recruitment Of Blue Crab, Callinectes Sapidus, Postlarvae To The Back-Barrier Lagoons Of Virginia's Eastern Shore, Robert D. Brumbaugh

OES Theses and Dissertations

Most research on the early life history of the blue crab, Callinectes sapidus, has been conducted in large partially stratified estuaries such as the Chesapeake Bay. In contrast, little is known about the recruitment dynamics or habitat requirements of blue crab postlarvae (megalopae) in shallow well-mixed lagoonal systems that make up a considerable part of the species' range. In Virginia's coastal lagoons, planktonic blue crab megalopae are most abundant at night on flooding tides, and are not abundant during the daytime or on ebbing tides. This appears to enhance retention within the lagoons, despite the short residence time of water …


The Effects Of Environmental Variability On The Population Structure Of The Eastern Oyster (Crassostrea Virginica): A Modeling Study, Margaret Mcmanus Dekshenieks Apr 1996

The Effects Of Environmental Variability On The Population Structure Of The Eastern Oyster (Crassostrea Virginica): A Modeling Study, Margaret Mcmanus Dekshenieks

OES Theses and Dissertations

Three models were coupled to investigate the effects of changes in environmental conditions on the population structure of the Eastern oyster, Crassostrea virginica. The first model, a time-dependent model of the oyster population as described in Powell et al. (1992) and Hofmann et al. (1992, 1995), tracks the distribution, development, spawning, and mortality of sessile oyster populations. The post-settlement model incorporates mortality through parasitism, predation, food depletion and extremes in environmental conditions. The post-settlement model supplies the initial abundance of larvae spawned into the water column, and in turn is the recipient of cohorts of spawn which survive through metamorphosis. …


Comparison Of Sapling Community Structure In Created And Natural Forested Wetlands In Southeastern Virginia, Sharon Ann Haines Apr 1996

Comparison Of Sapling Community Structure In Created And Natural Forested Wetlands In Southeastern Virginia, Sharon Ann Haines

Biological Sciences Theses & Dissertations

Forested wetlands are being destroyed at a rapid rate. Wetlands are valuable for flood control, aquifer recharge, and for their role in denitrification and storage of global carbon. When wetlands are lost, their functions and value to humans are lost as well. One response to the continued development of wetlands has been the artificial creation of new wetlands. This study compared the species density, relative density, coverage and frequency of occurrence of the woody vegetation in two southeastern Virginia created wetlands with that in two reference wetlands, also in southeastern Virginia, to determine the structural similarity of their respective communities. …


Seasonal And Mesoscale Variability In The Distribution Of Antarctic Krill, Euphausia Superba, West Of The Antarctic Peninsula, Cathy Meyer Lascara Apr 1996

Seasonal And Mesoscale Variability In The Distribution Of Antarctic Krill, Euphausia Superba, West Of The Antarctic Peninsula, Cathy Meyer Lascara

OES Theses and Dissertations

Observations collected between November 1991 and September 1993 during four multidisciplinary cruises were analyzed to provide a description of seasonal and mesoscale variability in the distribution and abundance of Antarctic krill, Euphausia superba, within continental shelf waters west of the Antarctic Peninsula and to investigate possible relationships between variability in krill distributions and variability in selected environmental parameters. Acoustic measurements of krill were made each season at designated locations to estimate the abundance of krill, in terms of vertically-integrated krill biomass and the number of aggregations, characterize the depth distribution of krill, and provide a quantitative description of the size, …


Factors Affecting Nitrogen Fixation Rates In Termites (Isoptera: Rhinotermitidae: Reticulitermes) And Termite Nitrogen Contributions Of Forest Ecosystems, Anthony Duane Curtis Apr 1996

Factors Affecting Nitrogen Fixation Rates In Termites (Isoptera: Rhinotermitidae: Reticulitermes) And Termite Nitrogen Contributions Of Forest Ecosystems, Anthony Duane Curtis

Biological Sciences Theses & Dissertations

Termites host symbiotic bacteria that fix atmospheric nitrogen, which makes termites important in the biogeochemical cycling of nitrogen in ecosystems. The objective of this study was to estimate annual nitrogen contributions by termites by examining seasonal rates of nitrogen fixation, seasonal abundance of different termite castes and their nitrogenase activity, the effects of dietary nitrogen on nitrogenase activity, and low oxygen and high carbon dioxide atmospheres on termite nitrogenase activity, and the accuracy of mark-recapture studies to estimate termite population size.

Termite nitrogen fixation rates were monitored monthly for 10 Reticulitermes Holmgren colonies from June, 1993, to December, 1995. Rates …


Association Between Nutrient Intake And Risk Of Coronary Heart Disease In California Seventh-Day Adventists, Peter Pribiš Mar 1996

Association Between Nutrient Intake And Risk Of Coronary Heart Disease In California Seventh-Day Adventists, Peter Pribiš

Loma Linda University Electronic Theses, Dissertations & Projects

Dietary habits are believed to be major determinants of risk of coronary heart disease (CHD). Studies of high and low risk populations have suggested several nutrients to be protective or hazardous against CHD. Most published work since 1984 on diet and CHD in the Adventist Health Study (AHS) population examined either foods or food groups. This study investigated ten nutrients as exposure variables and their relationship to CHD risk. A cohort of 23,616 nonsmoking, non-Hispanic white California Seventh-day Adventists was followed for six years beginning in 1976. Extensive dietary information was collected at baseline, as well as values of traditional …


The Evolution Of International Fisheries Management In The North Pacific Ocean And Prospects For The Future, Paul Augustus Flynn Jan 1996

The Evolution Of International Fisheries Management In The North Pacific Ocean And Prospects For The Future, Paul Augustus Flynn

Theses and Major Papers

The abundant resources of the North Pacific Ocean have been the subject of international disputes and negotiations through the 20th century. The management of species which range throughout this vast area, are not under the jurisdiction of a single state. That fact has required the establishment of a framework in which allocation and conservation measures can be researched and agreed upon. This has been accomplished through various multilateral and bilateral agreements. From the voluntary Japanese suspension of a directed salmon fishery off the coast of Alaska in 1938 to recently completed multilateral treaties, significant advances have been made in Pacific …


International Organizations And Tuna Management; Problems And Future Prospects, Yuh-Chen Chern Jan 1996

International Organizations And Tuna Management; Problems And Future Prospects, Yuh-Chen Chern

Theses and Major Papers

A large number of marine species migrate within and without national jurisdictions and a small number occur entirely outside any national jurisdiction. Thus, the species migrating through waters under the jurisdiction of coastal states to high seas beyond the jurisdiction of any single state are defined as highly migratory species (HMS). International organizations play a key role in the management of highly migratory species. Most of the international organizations concerned with HMS focus on tuna management.


Sacrificing Conservation For Pesos: An Analysis Of Select Marine Fisheries In The Political Environment Of Mexico, Sephen W. Bourgeois Jr. Jan 1996

Sacrificing Conservation For Pesos: An Analysis Of Select Marine Fisheries In The Political Environment Of Mexico, Sephen W. Bourgeois Jr.

Theses and Major Papers

The decline of most Mexican fisheries has occurred so rapidly that few Mexicans and Americans alike fully appreciate the loss. The major focus of this paper will examine the false impression that Mexico is engaging in marine conservation; in reality, its conservation efforts are responses to after-the-fact actions brought on by world critics and as a vehicle to pacify conservationists. The Mexican government can pass a law but lacks the resources to administer and enforce the law and subsequently manage its fisheries in an effective manner. Rather than survey the state of every fishery found in Mexican waters, this paper …


Trends In Abundance Of The Gulf Of Maine Population Of Harbor Porpoise, Paula Ann Olson Jan 1996

Trends In Abundance Of The Gulf Of Maine Population Of Harbor Porpoise, Paula Ann Olson

Theses and Major Papers

Hundreds of harbor porpoise die each year as bycatch in the Gulf of Maine's sink gillnet fishery. In recent years, concern has arisen whether the Gulf of Maine population of harbor porpoise can sustain this level of bycatch. It is believed that the population may have declined, or is declining as a result of the incidental moralities. This paper reviews what is known about Gulf of Maine harbor porpoise demographics and how that information is incorporated into the management of the porpoise/fishery interaction. Included in this paper is a new study on the trend of relative abundance of harbor porpoise …


Protection Of Marine Fish Habitat: Towards An Integrated Approach To Management, Andrea L. Oliver Jan 1996

Protection Of Marine Fish Habitat: Towards An Integrated Approach To Management, Andrea L. Oliver

Theses and Major Papers

This paper focuses on the problems associated with marine fish habitat protection and conservation at the federal level in the United States. The intent of the study is to provide a general overview of the issues, impacts, management problems and potential solutions. Federal statutory legislation that impacts marine fish habitat and agency authority derived from those legislative mandates are examined with a view toward promoting integrated management for marine biodiversity and overall ecosystem health. The concepts of coordinated and integrated approaches to management are discussed in the context of the present management regimes. Given the fragmented authority over the policy …


Limits To Private Aquaculture On Cape Cod, Kevin Robert Cute Jan 1996

Limits To Private Aquaculture On Cape Cod, Kevin Robert Cute

Theses and Major Papers

This study examined the potential of social conflict related to private and public rights, to constrain aquaculture on Cape Cod. While the ability of social conflict to constrain aquaculture has been demonstrated in a few cases, its current potential to constrain aquaculture on Cape Cod had not been established prior to this study. This study was based on information gathered from town records and public hearings related to proposed aquaculture ventures. In addition, town officials were interviewed to obtain additional information related to cases. The finding of this study is that private riparian proprietors, and interests in shell-fishing tend to …


The Role Of The Federal Aid In Sportfish Restoration Program In Promoting State Marine Artificial Reef Development Activities, Loren Clark Evans Jan 1996

The Role Of The Federal Aid In Sportfish Restoration Program In Promoting State Marine Artificial Reef Development Activities, Loren Clark Evans

Theses and Major Papers

The passage of the Wallop-Breaux Amendments to the Federal Aid in Sportfish Restoration Program (FASRP), in 1984, significantly increased the funding available to states participating in the Program. Subsequently, the FASRP became the largest single source of funding for state marine artificial reef development activities. In recent years, there has been concern among program constituents that FASRP funds are not being utilized as intended. The principle question of the current research focused on how effective FASRP subsidies have been in providing meaningful benefits to state fisheries management programs. Specifically, the research focused on the application of FASRP monies in promoting …


Public Health Hazards Associated With The Consumption Of Molluscan Shellfish In The State Of Rhode Island, Jeffrey F. Nussbaum Jan 1996

Public Health Hazards Associated With The Consumption Of Molluscan Shellfish In The State Of Rhode Island, Jeffrey F. Nussbaum

Theses and Major Papers

The principal objective of this thesis was to descriptively and empirically assess shellfish consumption hazards in the state of Rhode Island and to evaluate the use of a shellfish hazard warning label to modify unsafe consumptive behaviors. To accomplish this task, three research problems were examined using a survey instrument. The survey instrument was a questionnaire which included both closed and open-ended questions. The survey questions were designed to identify four primary research variables; shellfish consumptive behaviors, consumer knowledge of shellfish hazards and related government advisories, perceptions of risk regarding personal shellfish consumption, and response to warning label information. The …


Effects Of Periodic Environmental Hypoxia On Predator Utilization Of Macrobenthic Infauna, Janet A. Nestlerode Jan 1996

Effects Of Periodic Environmental Hypoxia On Predator Utilization Of Macrobenthic Infauna, Janet A. Nestlerode

Dissertations, Theses, and Masters Projects

Hypoxia and anoxia have significant deleterious ecological effects on living resources throughout many estuarine and marine ecosystems worldwide. Brief periods of low oxygen facilitate transfer of benthic production to higher trophic levels as many benthic infaunal species have shallower sediment depth distributions during hypoxic events. A baited time-lapse camera equipped with a water quality datalogger was used to document in situ exploitation of oxygen-stressed benthic invertebrate prey organisms by mobile fish and crustacean predators during alternating normoxia-hypoxia cycles in the York River. Based on photographic and diver observations, this hypoxiainduced benthic-pelagic transfer of production is more likely to occur when …


The Role Of Epibenthic Predators In Structuring Marine Soft-Bottom Communities Along An Estuarine Gradient, Rochelle D. Seitz Jan 1996

The Role Of Epibenthic Predators In Structuring Marine Soft-Bottom Communities Along An Estuarine Gradient, Rochelle D. Seitz

Dissertations, Theses, and Masters Projects

A unifying theory of community regulation in soft-bottom systems remains elusive, despite extensive field studies on factors controlling community structure. Here, I have (1) reviewed models of community regulation, (2) examined the role of predation in controlling benthic diversity along a salinity gradient, (3) examined effects of predation upon an abundant bivalve, Macoma balthica, and (4) revised a model of community regulation in an estuarine soft-bottom system. The Menge and Sutherland (MS) "consumer stress model" posits that consumers feed ineffectively in harsh environments, and the importance of physical disturbance, competition and predation varies with recruitment, environmental conditions, and trophic position. …