Thesis (M.S.)--University of Missouri-Columbia, 2003. / Typescript. Includes bibliographical references. Also available on the Internet.

Thesis (M.S.)--University of Missouri-Columbia, 2003. / Typescript. Includes bibliographical references. Also available on the Internet.

Thesis--Auburn University, 2009. / Abstract. Vita. Includes bibliographic records (p.23-29).

Thesis (M.S.)--Brigham Young University. Dept. of Biology, 2007. / Includes bibliographical references (p. 18-22).

archives@tulane.edu / Although interspecific competition and relevant coexistence mechanisms are core concepts in ecology and evolution, most such research has focused on two-species interactions. Lacking is important information on how and when interspecific competition operates in more complex species assemblages. This dissertation examined interspecific competition and coexistence mechanisms between a focal species, the American redstart (Setophaga ruticilla, Parulidae) and its potential competitors in multiple communities. Using a theoretical framework that builds on the well documented population ecology of redstarts, combined with interspecific dietary overlaps, I demonstrate ongoing interspecific competition. I found that species generally both overlap highly in diet and exhibit small, but consistent, differences consistent with their foraging behavioral differences. Although some competitive interactions were mediated by direct aggressive interactions, this research also highlighted diffuse competition as more important than previously recognized. My findings also differed from systems that have shown similar patterns insofar as high dietary overlaps persisted during times of resource scarcity, were driven by overlaps on low value prey taxa, and did not involve exclusive use of any resources by different competitors. All of these factors increase the potential negative demographic effects of interspecific competition, some of which have been documented in these bird species. A long history of competition studies in these warblers has shown large differences in foraging behavior among species, assumed to be what allows coexistence. However, it is not clear how and if differences in foraging behavior correspond to differences in resource use. I confirmed that locally coexisting study species differed almost completely in foraging behavior, particularly in microhabitat use. Likewise, using a variety of arthropod sampling methods, I found that microhabitats differed greatly in their available prey. Combining the large differences in foraging behavior with available prey significantly predicted the small dietary differences, although it did a poor job of explaining the already limited variation in diet. Overall, I found mixed support for behavioral niche partitioning, leading me to examine alternative mechanisms of coexistence. Contrary to past work focused on interspecific interactions, I found that population level forces dominate in determining local distributions, with birds of the same species being more evenly distributed due to intraspecific territoriality. This pattern led to higher local (point count scale) species richness, and greater community covariance than predicted. This intraspecific territoriality and repulsion is proposed as as a novel coexistence mechanism. / 1 / Cody M. Kent

Climate change is expected to have a profound impact on freshwater fish communities, especially at higher latitudes. In this study I investigated potential effects of climate change on the niche structure of Eurasian perch (Perca fluviatilis) by looking at their diet across a latitudinal gradient and at varying light climate. Dietary niche width of Eurasian perch did not differ significantly between boreal and temperate latitudes. Additionally, no significant difference in the prevalence of specialist individuals was found along the latitudinal gradient and water transparency levels. Habitat was the main factor that significantly affected niche width and level of specialization with both being significantly higher in the littoral habitat. Taken together my results suggest that climate change might indirectly affect niche patterns by altering fish densities through changes in productivity resulting in niche and specialization variation among habitats.

No description available.

A typical clinical cis-diamminedichloroplatinum (II) (cisplatin) dosing regimen consists of repeated cycles of five to seven daily low dose treatments followed by a one to two week recovery period. While effective, this dosing structure results in a prolonged, and sometimes permanent, infertility in men. Undifferentiated spermatogonia, including spermatogonial stem cells (SSCs), are theoretically capable of repopulating the seminiferous tubules after exposure has ceased. It is proposed that an altered spermatogonial environment during recovery from the initial treatment cycle may drive an increase in SSC mitotic cell activity, rendering the SSC pool increasingly susceptible to cisplatin-induced cell death from subsequent cycles. The undifferentiated spermatogonia population and niche of the adult mouse (C57/BL/6J) were examined during the recovery period of a clinically-relevant course of one and two cycles of 2.5 mg/kg/d of intraperitoneal cisplatin and were compared to mice receiving an equivalent cumulative dose in a single cycle (5.0 mg/kg/d) and vehicle treated controls. Histological examination of the testicular epithelium revealed an increase in the disorganization of spermatogenesis correlating with the number of exposure cycles. Quantification of TUNEL positive cells showed an increase in apoptotic germ cells early in the recovery period in mice exposed to cisplatin compared to control animals. Immunohistochemical (IHC) examination of Foxo1 (undifferentiated spermatogonia marker) showed an increase in the undifferentiated spermatogonia population late in the recovery period in mice exposed to one cycle of 2.5 mg/kg/d, but not following two cycles of 2.5 mg/kg/d. Analysis of BrdU incorporation after dosing indicated a decrease in mitotic activity of early germ cells immediately after cisplatin exposure followed by a return to basal levels by the conclusion of the initial recovery period. No such rebound was observed during the second recovery period. IHC investigation of glial cell line-derived neurotrophic factor (GDNF), a recognized SSC niche factor, revealed an increase in production along the basal Sertoli cell membrane throughout the recovery period in all treatment groups. Taken together, these data establish that the impact of cisplatin exposure on the functional stem cell pool and niche correlates with: (1) the number of dosing cycles; (2) mitotic activity of early germ cells; and (3) alterations in the basal Sertoli cell GDNF expression levels after cisplatin-induced testicular injury. / text

Thesis (Ph.D.) in Oceanography--University of Maine, 2007. / Includes vita. Includes bibliographical references (leaves 155-172).

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references. Also available on the World Wide Web.