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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
881

THE ROLE OF TEMPERATURE IN THE DISTRIBUTION OF MIXOTROPHIC PROTISTS OF THE GENUS DINOBRYON

Heinze, Adam Wesley January 2009 (has links)
Mixotrophic organisms utilize both photosynthetic and phagotrophic nutritional modes and are increasingly recognized as important contributors to aquatic food webs. Dinobryon, a widespread freshwater genus of mixotrophs had dramatic seasonal and annual variation in Lake Lacawac, a mesotrophic kettle lake in northeastern Pennsylvania. Although light is required for population growth in Dinobryon, it does not appear to control vertical distribution patterns observed during a 3-year survey. One year, the maximum annual abundance was observed close to the surface, while the following year the maximum annual abundance occurred at 4 m depth where light levels were <2% of surface irradiance. The depth of maximum Dinobryon abundance during the second year overlapped with an oxygen maximum at 4 m, which strongly suggests effective photosynthesis at a relatively low light level. Analysis of the distribution data suggests that temperature may be a primary driver of Dinobryon spp. distribution in the water column of this lake. Although annual variability in absolute abundance was high, peak Dinobryon biomass always occurred within a narrow range of temperature (10°-16°C). This distributional study was validated by an early spring field experiment where temperature was raised with water heater to 16° C. The abundance of Dinobryon increased two-fold at the higher temperature. A novel laboratory instrument was developed and constructed that established a vertical temperature gradient with even lighting to test the ability of Dinobryon to congregate within that specific temperature range independent of light intensity. Dinobryon abundance in the column was maximum within the same range of water temperatures observed in the field study. Because lighting was even across the vertical water column, any effect of light attenuation in the lake distribution was eliminated and accumulation due to temperature effects was confirmed. With climate change becoming more apparent, it is clear that understanding temperatures role in the distribution of the aquatic food web is timely and important. / Biology
882

Regulators of stream ecosystem recovery from disturbance

Murdock, Justin N. January 1900 (has links)
Doctor of Philosophy / Department of Biology / Walter K. Dodds / Streams exist in a state of dynamic equilibrium with frequent floods and drought. The frequency and intensity of stream disturbances are projected to increase with greater water withdrawal for agriculture and biofuel production, watershed development, and altered climate. Changes in the hydrologic regime may alter stream ecosystems. I studied how stream communities return after disturbances and how nutrients, consumers, and substrata heterogeneity influence recovery trajectories. Large consumers were excluded from pools following a severe drought to assess how community structure and function returned in their absence. Large consumers reduced algal biomass, primary productivity, and nutrient uptake rates, and delayed macroinvertebrate recolonization. However, grazer effects were temporary and their influence weakened after five weeks. In a second experiment, I assessed the relative influence of grazer density and nutrient loadings on algal recovery from flood. Nutrients had a stronger effect on recovery than grazers, but the strength of each varied temporally. Grazer control decreased and nutrient control increased over time. A third experiment addressed the physical properties of stream substrata on algal development. The relationship among algal accumulation and substrata surface topography was assessed by growing algae on substrata with varying orientation and roughness. Total algal biomass decreased on surfaces with angles > 45 degrees, and peaked at an intermediate roughness (pit depth of [similar to]17 [Mu]m). Rougher surfaces collected more tightly attached (grazer resistant) forms and less loosely attached (grazer susceptible) forms. Individual algal forms responded differently to grazing pressure, nutrient availability, and surface features. I developed a method using Fourier-transform infrared microspectroscopy to measure single-cell physiological responses in benthic algae. Nutrients and consumers were strong regulators of ecosystem succession following disturbance, but nutrient influence was stronger. The influence of nutrients and consumers were context dependent, and changed over the course of recovery. Rougher surfaces increase algal growth and shifted algal assemblages to more grazer resistant forms, which may decrease the influence of large consumers on stream function. Altering the severity and frequency of disturbances can change the trajectory of stream recovery and ultimately change community composition and stream metabolic activity, which may alter ecosystem services such as water purification and recreation.
883

Structure and function of two urban forest stands in Tucson, Arizona

Sacamano, Paul, 1962- January 1991 (has links)
The purpose of this study was to describe the structures of an arid urban forest. Two distinct and adjacent residential neighborhoods in Tucson, Arizona, Winterhaven and Richland Heights, were chosen as the study site. Landcover classes were identified through aerial photointerpretation and digitized using AutoCad. A field inventory gathered vegetative measures. Through an analysis, species composition, horizontal and vertical structure were described. Results were compared between each neighborhood stand and among findings of previous structural studies. Results describe Winterhaven as an uneven-aged stand with 55% available growing space, 37% canopy stocking, a pattern of strong dominance and mostly exotic species. Richland Heights is an even-aged stand with 78% available growing space, 11% canopy stocking, a pattern of codominance and mostly native species. These and other structural analyses have provided a descriptive study of two arid urban forest stands.
884

Summer habitat use by Apache trout (Oncorhynchus apache) in five streams on the Fort Apache Indian Reservation

Wada, Lorena Lai Lin, 1963- January 1991 (has links)
In the summer, five creeks on the Fort Apache Indian Reservation were examined. Apache trout generally selected the deepest pools with the greatest amounts of instream cover and bankcuts. Though fish in three creeks may be Apache trout x rainbow trout hybrids, they were found to occupy the same type of pools. Regression models on environmental conditions in two creeks accounted for 83% and 76% of the variability in biomass of Apache trout. There was adequate nursery habitat (and successful reproduction) on two creeks, but such habitat was lacking in the other three creeks, and no evidence of successful reproduction was found. There was little evidence of survival of smaller Apache trout in areas of co-occurrence with non-native trouts but there was evidence of their survival upstream where fewer numbers of non-natives occur. The exclusion of smaller Apache trout may be from elimination or emigration. Greater populations of Apache trout may be supported through eradication of non-native trouts, the addition of instream cover, and structures designed to create longer lasting pools and bankcuts.
885

Sprouting response of Quercus arizonica and Quercus emoryi following fire

Babb, Geoffrey Dean, 1957- January 1992 (has links)
Sprouting response of Quercus emoryi and Quercus arizonica was studied following a May, 1987 wildfire on the Audubon Society Research Ranch Preserve in Santa Cruz, Co., AZ. Sprouting response of oaks was measured as total number and density of sprouts by species and diameter class. Thirty-five of the 109 trees examined (32%) sprouted in response to the fire, including 30.5% of all Q. emoryi and 36.4% of all Q. arizonica. In both species, small diameter (10 cm) trees are more likely to sprout than those larger than 10 cm. Quercus emoryi trends toward producing more sprouts/tree than Q. arizonica (avg. of 14.03 sprouts to 6.87 sprouts). Among all sprouters, however, there is no difference in the number of sprouts produced by trees in the two size classes. Sprout density is greater in Q. emoryi at 3.58 sprouts/cm. Q. arizonica averages 0.89 sprouts/cm. In all sprouters, density is greater in smaller stems (4.17 sprouts/cm) compared with 0.71 sprouts/cm in the larger size class.
886

Summer habitat use by Sonora chub in Sycamore Creek, Santa Cruz County, Arizona

Carpenter, Jeanette, 1960- January 1992 (has links)
The Sonora chub (Gila ditaenia) is a small minnow that is federally-listed as threatened. My research objectives were to quantify characteristics and persistence of macrohabitats used by this species through critical summer periods, and to quantify microhabitat selection in Sycamore Creek, Arizona. By the end of the summer drought, macrohabitats containing adults were deeper, larger and decreased less rapidly than areas with only immature fish or unoccupied areas. Loss of surface area was highest in inundated unoccupied areas and areas with only immature fish. Loss of Sonora chub from drying pools was highest in pools with immature fish. Ephemeral and unoccupied areas had higher percentages of floating algae and coarser substrates than persistent, occupied areas. General microhabitat characteristics selected by Sonora chub were areas with bedrock or fine substrates near cover and zero velocity. Microhabitat use usually differed among life stages, and availability and selection varied among pools.
887

Distribution and abundance of fishes in Shinumo Creek in the Grand Canyon

Allan, Nathan Layne, 1968- January 1993 (has links)
Bluehead sucker (Catostomus discobolus) and speckled dace (Rhinichthys osculus) were the only native species in Shinumo Creek above a waterfall located about 120 m upstream from the confluence of Shinumo Creek and the Colorado River. Rainbow trout (Oncorhynchus mykiss) was the only introduced species found upstream of the waterfall. I attribute the coexistence of the native and introduced species is attributed to differential use in resources and the similarly small size of bluehead sucker and rainbow trout. Mean total length of bluehead suckers was 160 mm and the largest fish captured was 230 mm (n = 77). Mean length of rainbow trout was 149 mm (maximum = 300 mm; n = 46). Bluehead suckers in Shinumo Creek were smaller than individuals observed in the mainstem Colorado River. Small size may be a response to the decreased size of the habitat available. The permanence of the waterfall barrier near the mouth of Shinumo Creek is a result of regulation of the Colorado River that prevents inundation of the waterfall.
888

Selenium levels in selected species of aquatic birds on Imperial National Wildlife Refuge

Martinez, Cynthia Therese, 1969- January 1994 (has links)
Five species of waterbirds were collected from five sites on Imperial National Wildlife Refuge between April and August of 1993. There were previous baseline contaminants data for all sites. Sites were of two distinct habitat types. Backwater lakes have a direct connection to the mainstem of the Colorado River, and seep lakes receive river water only via seepage through the soil column. Selenium concentrations in liver, kidney, and muscle tissues were consistently higher in birds collected from backwater lakes than those collected from seep lakes. Eighty-one percent of the birds collected on backwater lakes (n = 52) were above the effect threshold for reproductive impairment or embryotoxicity (10 ppm dry weight in livers). Herbivorous birds had significantly (p ≤ 0.05) lower tissue selenium levels than those species feeding on animal matter. Of the birds feeding on fish and invertebrates, 83% (n = 47) had selenium levels in liver above the effect threshold. Differences in selenium concentrations based on diet suggest food chain cycling of selenium. Eggs from waterbirds as well as those from neotropical migrants were above the 3 ppm embryotoxicity threshold.
889

Arroyo Chico: The effects of design and management on the biological and social aspects of an urban wash

Barber, Richard Henry, 1942- January 1995 (has links)
Arroyo Chico Wash, an important drainage for central Tucson, Arizona, runs through numerous neighborhood and industrial areas before emptying into the Santa Cruz River. Within four suburban neighborhoods along the wash, direct observations, personal interviews, survey questions, and historical documents are used to describe design and management influences on the biological and human aspects of the wash. Plants along the wash are identified by 2-meter wide belt transects run at 100-meter intervals over the 4 kilometer length of the study area. Wild animal and bird lists are based on observation and information given by residents. Relationships between design, maintenance and neighborhood attitudes toward the wash are assessed using a survey questionnaire given to people living adjacent to the wash. Results show the wash in the Colonia Solana neighborhood has the greatest biological diversity, highest neighborhood satisfaction and highest recreational use. In neighborhoods where the wash is a "backyard easement", satisfaction and use are the lowest.
890

Feeding and oviposition behavior of tobacco hornworms, Manduca sexta, in relation to Myo-inositol

Nelson, Nancy Marie, 1968- January 1996 (has links)
The purpose of this thesis is to examine the role that myo-inositol plays in feeding and oviposition by the tobacco hornworm, Manduca sexta. The results show that; (1) of all of the compounds tested only myo-inositol and epi-inositol consistently elicited a rapid, phasic-tonic firing response from taste receptors, (2) inositol is a feeding stimulant for both fifth and third stage M. sexta larvae, (3) M. sexta larvae do not need dietary inositol for normal growth and development, but females need dietary inositol as larvae for egg production as adults, (4) inositol is also a utilizable carbohydrate for M. sexta larvae and considering its relative abundance in Solanaceous plants, it may serve as an important carbohydrate source, (5) inositol does not appear to be important in oviposition, (6) inositol is correlated to protein levels in young tomato and tobacco plants.

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