Braunschweig, Techn. Universiẗat, Diss., 1999.

Undergraduate honors paper--Mount Holyoke College, 2008. Dept of Biological Sciences. / Includes bibliographical references (leaves 42-45).

No description available.

Globally, human modification of land and the human-aided introduction of exotic species are considered to be the main drivers behind species decline and extinction. Human colonisation of New Zealand and subsequent development resulted in the conversion of native forests and shrublands into productive land, which together with the introduction of invasive species has caused the decline of many species, and many more are now threatened with extinction. This issue is particularly prevalent in the lowland eastern areas of the South Island, in which there has been intensive land development. One strongly affected group are species within the genus Olearia, in which several species are threatened with extinction, including nationally declining Olearia lineata. In contrast, other species in this genus, such as non-threatened O. bullata, are seemingly not as strongly impacted. My study investigated the mechanisms behind why O. lineata is nationally declining in comparison to the non-threatened congener O. bullata. To do this, I investigated two main research questions; one question investigated the demographic structure of populations to determine if regeneration is occurring and the vegetation composition of the surrounding community. Sampled populations indicated regeneration failure in O. lineata populations but also in O. bullata populations, despite its non-threatened status. I found that a high proportion communities contained exotic grasses, therefore, the second question was how the presence of the exotic grass- Agrostis capillaris, affected recruitment of O. lineata and O. bullata. Two glasshouse experiments investigated how the presence or absence of grass affected germination and growth of seedlings. Both Olearia species were found to germinate in the presence of grass, but seedlings grew significantly better in the absence of grass. Olearia are also important native Lepidoptera hosts as a suite of native moths feed exclusively on this genus. Therefore, a third research question investigated the abundance of larvae and the community composition of Lepidoptera on O. lineata and O. bullata in comparison to another Lepidoptera host Coprosma propinqua. Moth larvae were collected and some species successfully reared to find there was higher larvae abundance on O. lineata and high species overlap between O. lineata and O. bullata with little species overlap between the two Olearia species and C. propinqua. Overall, my research found that exotic invasive grasses potentially cause regeneration failure in both O. bullata and O. lineata. However, the largest impact in the difference of threat status is due to O. lineata populations occurring in the most developed lowland areas of the eastern South Island, whereas O. bullata populations occur in less human modified, higher altitude areas. The further development of these areas through human activity threatens the future persistence of these Olearia species and the future of the Olearia Lepidoptera specialists.

The seedling-infecting pathogen Ustilago bullata Berk. is a naturally occurring biological control agent for cheatgrass (Bromus tectorum L.). The effects of temperature and nutrients on pathogen teliospore germination behavior and the effects of temperature on host seed germination were examined. The effects of temperature on sporidial proliferation, host infection in a temperature-controlled environment and in a field setting for eight populations were investigated. The infection success of Ustilago bullata on Bromus tectorum in cultivated fields as a function of seeding date, inoculation method, inoculum density, supplemental watering, and litter was also investigated. Teliospores germinated faster on potato dextrose agar than on water agar. Teliospores germinated slowly at temperatures far from the optimum of 15 and 20 C. There were among population variations in teliospore germination and sporidial proliferation, but differences among populations were much more pronounced at temperatures below 15 C. Infection also decreased and varied far from the optimum with almost no infection at 2.5 C in a controlled-environment and in the field for the December-planted seeds. Warmer early fall rather than the colder late fall was suitable for successful infection. This agreed with both laboratory and controlled-environment experiments. Intratetrad mating was observed with teliospores at 2.5 C. Teliospore germination tracked seed germination closely with teliospore germination rate exceeding the host seed germination rate over the range of 10 to 25 C where both were measured. Below 10 C, teliospore germination rate fell below host seed germination. This phenomenon was associated with lower infection percentages, suggesting that teliospore germination needed to be ahead of the seed for maximum infection. Inoculum density was positively correlated with infection rate. Litter significantly increased infection, while supplemental watering significantly increased plant establishment. Since teliospores from different populations showed similar germination patterns at temperatures typical of autumn seedbeds in the Intermountain West, it may not be necessary to use locally-adapted pathogen populations in biological control program. A biocontrol program is most likely to be effective under a scenario where autumn precipitation permits emergence of most of the host seed bank as a fall cohort.