11 Matching Results

Results open in a new window/tab.

Life Histories Behavior and Space Partitioning in Selected Species of Western North American Plecoptera (open access)

Life Histories Behavior and Space Partitioning in Selected Species of Western North American Plecoptera

Five species of stoneflies (Zapada haysi, Plumiperla diversa, Taenionema pacificum, Isoperla petersoni, Arcynopteryx compacta) from the North Slope and Interior of Alaska were examined for seasonal patterns of emergence of adults and growth of nymphs. Generally growth was retarded during the winter in this region, and all species except I. petersoni completed growth prior to January. The life cycles of six stonefly species (Prostoia besametsa, Triznaka signata, Sweltsa coloradensis. Isoperla fulva, Skwala parallela, Claassenia sabulosa) are described from northern New Mexico. In this region growth was generally less retarded during the winter than in Alaska; P. besametsa completed all nymphal growth during late fall and winter. Drumming behavior of a Colorado population of Pteronarcella badia was described using an evolutionary framework to explain the maintenance of signal variation in this species. Laboratory experiments were used to explore the effect of intraspecific and interspecific interactions on spatial partitioning in P. badia and Claassenia sabulosa. P. badia exhibited clumping and distributed itself as the surface area of substrate in low densities; however, in the presence of C. sabulosa its distribution was random and different from available surface area. A field study was used to examine spatial partitioning by three New Mexico stonefly …
Date: August 1988
Creator: Hassage, Rodney Lynn, 1947-
System: The UNT Digital Library
Pre-Impoundment Estimations of Nutrient Loading to Ray Roberts Lake and Prediction of Post-Inundation Trophic Status (open access)

Pre-Impoundment Estimations of Nutrient Loading to Ray Roberts Lake and Prediction of Post-Inundation Trophic Status

Excessive nutrient loading of natural and artificial lakes has led, in some systems, to plethoric algal and aquatic macrophyte growth which can result in aesthetic degradation and undesirable tastes and odors. It would be advantageous to have some indication of the potential trophic status of a reservoir before it is filled. An objective of this study was to assess the water quality and nutrient loading potential of the tributaries entering Ray Roberts Lake, a large reservoir located in north central Texas. Samples from a maximum of thirteen sites were collected on the Elm Fork, Trinity River, Isle duBois Creek, and five additional tributaries. Data were also collected during six storms, from atmospheric deposition collectors, and from soil-water microcosms. The relationship between watershed landuse and mean water nutrient concentrations was evaluated. Significant differences will exist between the two major arms of Ray Roberts Lake: Elm Fork, Trinity River and Isle duBois Creek. While the majority of the annual phosphorus and nitrogen load entering both tributaries is coming from overland flow, the proportion is higher in Isle duBois Creek. Point sources in the Elm Fork contribute a larger percentage of the bioavailable phosphorus, which is significantly greater than in Isle duBois Creek. …
Date: May 1988
Creator: Pillard, David Alan, 1958-
System: The UNT Digital Library
Multivariate Analyses of Amphibian and Reptilian Distribution in Texas (open access)

Multivariate Analyses of Amphibian and Reptilian Distribution in Texas

Presence-absence data for amphibians, chelonians, saurians, ophidians, and the terrestrial and aquatic ecological guilds of reptilians were analyzed using multivariate analyses. Geographically consistant distributional patterns were found for all faunal groupings. The correspondence between analyses of the different taxa and guilds was not perfect, but similarities were found. All analyses agreed on the presence of a distinctive region in east Texas. Most analyses also agreed on the presence of distinctive regions in south Texas, the Trans-Pecos, the Edwards Plateau, and north-west Texas. There is strong correspondence between interpretations of the analyses based on the amphibian, saurian, ophidian, and terrestrial reptilian distributions, and the biotic provinces produced by earlier, subjective analyses. The Edwards Plateau and a region on the western periphery of east Texas were found to be transitional between other, more faunally distinctive areas for most fauna! groups. Detailed examination of these regions suggested they are best described as clinal in nature. The environmental variables which were most effective in explaining patterns in the distribution of the various taxa and guilds were related to precipitation. However, variations in temperature and physiography were also important predictors of distribution for several of the groups. The distributions of soil and vegetation associations were …
Date: August 1988
Creator: Ward, Rocky
System: The UNT Digital Library
Physiological Responses of Myriophyllum spicatum to Time Varying Exposures of Diquat, 2,4-D and Copper (open access)

Physiological Responses of Myriophyllum spicatum to Time Varying Exposures of Diquat, 2,4-D and Copper

The physiological responses of Myriophyllum spicatum to 2,4-D, diquat and copper were quantified using a plant tissue viability assay, and daily measures of dissolved oxygen and pH. Correlations of herbicide tissue residues to physiological response measures were determined and the relationship was used to develop exposure-response models. Diquat and copper had a greater effect on plant tissue viability than was observed for 2,4-D. Diquat produced greater reductions in dissolved oxygen concentrations and pH values than 2,4-D or copper. Copper exposure had the least effect on these parameters. Exposure-response models developed for 2,4-D predicted effective control at plant tissue residues ranging from 4000 to 4700 mg/kg. Aqueous exposure concentrations necessary to produce effective control plant tissue residues ranged from 0.20 to 0.40 mg/L. Exposure-response models developed for diquat predicted effective control at plant tissue residues ranging from 225 to 280 mg/kg. Aqueous exposure concentrations necessary to produce effective control plant tissue residues ranged from 0.113 to 0.169 mg/L. Exposure-response models developed for copper predicted effective control at plant tissue residues ranging from 680 to 790 mg/kg. Aqueous exposure concentrations necessary to produce effective control plant tissue residues ranged from 0.32 to 0.64 mg/L. Model predictions for 2,4-D, diquat and copper were …
Date: May 1988
Creator: Rocchio, Patricia Mary
System: The UNT Digital Library
Genetic Differentiation of the Geomys Pocket Gopher Complex of Texas (open access)

Genetic Differentiation of the Geomys Pocket Gopher Complex of Texas

Genetic variation was analyzed for populations of seven taxa comprising four cytotypes of the Geomys bursarius chromosome complex, including G. b. major, G. b. knoxjonesi, and the Edwards Plateau taxa, G. b. llanensis and G. b. texensis. Genetic relationships of the Edwards Plateau gophers with other taxa and between themselves were examined. Genetic similarity, number of fixed allelic differences, and ectoparasite distribution indicate the Edwards Plateau gophers are a distinct gene pool. Isolation of the Edwards Plateau taxa precludes contact zone analysis. However, genetic differentiation is typical of that between other species of Geomys, and the Edwards Plateau taxa should be recognized as G. texensis. Distributions of allelic frequencies indicate little justification in retaining the subspecific status of the Edwards Plateau forms.
Date: August 1988
Creator: Block, Scott B. (Scott Bishop)
System: The UNT Digital Library
Quantitation of Endogenous Nucleotide Pools in Pseudomonas aeruginosa (open access)

Quantitation of Endogenous Nucleotide Pools in Pseudomonas aeruginosa

Nucleotide pools were extracted and quantified from Pyr^+ and Pyr^- strains of P. aerucjinosa. Strains were grown in succinate minimal medium with and without pyrimidines, and nucleotides were extracted using trichloracetic acid (TCA; 6% w/v). The pyrimidine requirement was satisfied by uracil, uridine, cytosine or cytidine. Pyr^- mutants were starved for pyrimidines for two hours before nucleotide levels were measured. This starvation depleted the nucleotide pools which were restored to wild type levels by the addition of pyrimidines to the medium. When the pyrimidine analogue, 6-azauracil, known to inhibit OMP decarboxylase, was added to cultures of the wild type strain, the uridine and cytidine nucleotides were depleted to near zero. Thus, the nucleotide pool levels of Pseudomonas strains can be manipulated.
Date: August 1988
Creator: Entezampour, Mohammad
System: The UNT Digital Library
The Effect of N, N Bis (ethylene)-P (1-adamantyl) Phosphonic Diamide on Rous Sarcoma Virus (open access)

The Effect of N, N Bis (ethylene)-P (1-adamantyl) Phosphonic Diamide on Rous Sarcoma Virus

The drug, N,N bis (ethylene)-P (1-adamantyl) phosphonic diamide inhibits focus formation of Rous Sarcoma Virus in tissue culture. Transformation of chick cells was inhibited when the drug was added to chick cells prior to infection. The drug did not inhibit the transformation of Normal Rat Kidney Cells infected with RSV, when the cells were grown at non-permissive temperatures and shifted to permissive temperatures upon addition of the drug. Nor did the drug revert cells transformed at permissive temperatures. These studies indicated that the inhibition of RSV is in the early stage of viral growth, possible penetration or uncoating.
Date: March 1988
Creator: McGraw, Thomas L. (Thomas Lee)
System: The UNT Digital Library
Environmental Correlates to Genetic Variation in the Coral Reef Fish, Thalassoma bifasciatum (open access)

Environmental Correlates to Genetic Variation in the Coral Reef Fish, Thalassoma bifasciatum

Genetic variation was examined in bluehead wrasse, Thalassoma bifasciatum, populations along the Florida Keys. Interpretion of mean heterozygosity (H), percent polymorphic loci per population (P), genetic similarity, and F and G statistics demonstrated a clear division of wrasse populations into "northern" and "southern" groups. Correlation and cluster analyses indicated the six reefs can be grouped in a similar fashion based on genetic and environmental data. The conclusion from this analysis of wrasse populations in the Florida Keys is that substantial population subdivision occurs in response to differing selective pressures created by heterogeneous environments.
Date: December 1988
Creator: Pirkle, Michelle S. (Michelle Serpas)
System: The UNT Digital Library
A Habitat Evaluation and Management Plan for a Riparian Ecosystem (open access)

A Habitat Evaluation and Management Plan for a Riparian Ecosystem

Ecological research involving habitat studies was conducted on the Elm Fork of the Trinity River in Denton County, Texas, from spring 1985 to spring 1986. Habitat Evaluation Procedures and Habitat Suitability Index Models developed by the United States Fish and Wildlife Service were applied to a 1419 hectares study area to determine the quality of habitat for four species: beaver, Castor canadensis, wood duck, Aix sponsa, pileated woodpecker, Dryocopus pileatus, and white crappie, Poxomis annularis. Population estimates were generated. A wildlife management plan was developed for the study area. Habitat Suitability Index Models were found to be overly conservative, underestimating the quality of habitat in areas of ecological transition.
Date: May 1988
Creator: Wilkinson, Robert N.
System: The UNT Digital Library
Neuronal Survival After Dendrite Amputation: Investigation of Injury Current Blockage (open access)

Neuronal Survival After Dendrite Amputation: Investigation of Injury Current Blockage

After dendrite transection, two primary injury current pathways may acount for cell death: (1) the lesion current at the site of injury and (2) the voltage sensitive calcium channels along the dendrite. Lesions were made with a laser microbeam in mouse spinal monolayer cell cultures. Polylysine was tried as a positively charged "molecular bandage" to block the lesion current. The calcium channel blockers, verapamil and nifedipine, were used to reduce the calcium channel current. Control toxicity curves were obtained for all three compounds. The results show that neither verapamil, nifedipine, nor polylysine (MW: 3,300) protect nerve cells after dendrite amputation 100 ptm from the soma. The data also indicate that these compounds do not slow the process of cell death after such physical trauma.
Date: December 1988
Creator: Shi, Ri Yi
System: The UNT Digital Library
Niche Structure of an Anole Community in a Tropical Rain Forest within the Choco Region of Colombia (open access)

Niche Structure of an Anole Community in a Tropical Rain Forest within the Choco Region of Colombia

Ten species of anoles at Bajo Calima within the Choco of Western Colombia separate into two principal microhabitat groups: forest species, and those inhabiting openings and edges. The ten anoles further separate according to ground and vegetation dwellers. There is a relation at Bajo Calima between the number of anole species and vegetational structural diversity. Anole diversity within a given macrohabitat is by perch microsite/microclimate heterogeneity. These are the two major ecological dimensions along which similarity is limited or resources are partitioned.
Date: May 1988
Creator: Castro-Herrera, Fernando
System: The UNT Digital Library