The main objective of this study was to examine the effects of intraspecific competition on the growth and reproduction of yellow nutsedge. A field experiment was conducted to examine twelve tuber densities of yellow nutsedge, ranging from 1 to 1000 tubers/m$ sp2$. Results indicate that spring tuber populations of 100 tubers/m$ sp2$ and lower require close to 100% control of the infestation in order to prevent the yellow nutsedge population from increasing. Yellow nutsedge spring tuber population does not appear to influence tuber distribution in the soil profile. All tuber densities examined produced the greatest proportion of tubers in the top 20 cm of the soil profile. Tuber and shoot production increased as initial yellow nutsedge tuber populations increased from 1 to 1000 tubers/m$ sp2$, as did tuber and shoot biomass. Consequently, intraspecific competition does not appear to come into effect at tuber populations of 1000 tubers/m$ sp2$ and less. / Predictions were made to determine the spread of yellow nutsedge based on an infestation of a single tuber. A single yellow nutsedge tuber could grow to infest an area of 50 m$ sp2$ in 5 years. Information concerning the effect of spring tuber density on the reproduction and spread of yellow nutsedge should be used in formulating control strategies for this weed.

Typescript. / Thesis (Ph. D.)--University of Hawaii at Manoa, 1990. / Includes bibliographical references (leaves 156-169). / Microfiche. / ix, 169 leaves, bound ill. 29 cm

Thesis (Ph.D.). / Written for the Depts. of Anthropology and Biology. Title from title page of PDF (viewed 2008/02/12). Includes bibliographical references.

Thesis (Ph. D.) -- Lincoln University, 2008. / Also available via the World Wide Web.

Thesis (Ph.D.)--University of Delaware, 2008. / Principal faculty advisor: Ronald Henry Karlson, Dept. of Biological Sciences. Includes bibliographical references.

Thesis (M.A. in anthropology)--Washington State University, May 2009. / Title from PDF title page (viewed on June 8, 2009). "Department of Anthropology." Includes bibliographical references (p. 40-45).

No description available.

Juvenile steelhead are known to associate with shiner groups, though they also compete for food. Steelhead form dominance hierarchies within cohorts and aggressively defend feeding territories against all other fish. This study focused on the differential effect of shiner competition on steelhead of different social standing. Survival of subordinate juvenile steelhead was significantly enhanced by the presence of redside shiner under laboratory conditions. A factorial experiment in 80 L tanks examined the relative effects of 0, 3, and 9 shiner at 15�� and 20��C on the growth and survival of 3 juvenile steelhead per tank. No temperature effect was detected and there was no significant difference in steelhead growth though statistical power was low (n=5). The largest steelhead did not die in any treatment and no steelhead died in the presence of 9 shiner. In treatments where no shiner were present mortality in the smallest steelhead was 80% (p-value<0.01). Aggressive interactions between steelhead allowed pathogens to colonize breaks in the skin of stressed fish resulting in death. In 6800 L recirculating stream channels with natural substrate, 10 steelhead were held either alone or with 20 shiner at 15��C. No steelhead died and their growth was not significantly different between treatments, but, in the absence of shiner fin damage was 16 times greater (p-value<0.01) in the smallest three steelhead. If a shiner group was present the smallest steelhead appeared to shoal with shiner to avoid attack by dominant steelhead. / Graduation date: 1999

Elton (1927) realized that, intuitively at least, nature was complex and stable. And that the last property contributed to the first. This idea was challenged mathematically by Gardner and Ashby (1970) and May (1972), and in the years following various models have attempted to reconcile these opposing views. Unlike previous mathematical approaches that demonstrated that simple stable systems are destabilized through added complexity, the approach presented herein began with a model that was unstable. This perspective provided allows model complexity and at the same time increased likelihood of mathematically stable. This novel observation suggested that ecosystem complication might stabilize a community. Within these models a system may be stable despite the coexistence of several competitors, in direct opposition to the Competitive Exclusion Principle. The hypothesis that the principle may not hold as an absolute generality beyond two competitors is proposed. This paradox may be explained by (1) interactions between competitors, (2) a keystone predator, or (3) a combination of the first two factors. / Graduation date: 1999

Heterothallic, facultatively sexual populations are vulnerable to the loss of a mating type by natural selection during periods of asexual reproduction. Experiments are described which demonstrate a competitive difference between the mating types of Chlamydomonas reinhardtii, a unicellular green alga with two isogamous mating types, mt + and mt $-.$ When grown vegetatively under phototrophic (light) conditions, mt + outcompetes mt $-.$ Assays of the growth parameters of isolated spores suggest that mt + has a higher growth rate than mt $-$ in the light, and that mt $-$ has a higher growth rate than mt + in heterotrophic (dark) growth conditions. / A literature review shows that sampling from natural populations of heterothallic, facultatively sexual species often yields only one mating type or significantly skewed mating-type distributions. This indicates that competition between mating types and the consequent loss of one mating type may be common in these populations. / A discussion of current theories on the evolution of heterothallism as well as the results of a simulation model reveal that heterothallism will spread if any fitness reduction is suffered by in-crossing homothallic individuals. However, fitness differences between the heterothallic alleles allow the invasion of a homothallic allele into a heterothallic population. / The implications of mating type competition on the maintenance and distribution of heterothallic populations in nature are discussed. It is argued that heterothallic, facultatively sexual populations commonly lose the potential for sex because of the loss of one mating-type allele. The prediction is made that homothallism is more common among facultatively sexual organisms than it is among obligately sexual organisms.