Impacts of habitat alteration and predispersal seed predation on the reproductive success of Great Basin forbs.

摘要

Sexual reproductive success in wild plant populations is dependent upon the ability to bank seed for when environmental conditions favor seedling recruitment. Seed production in many plant populations requires the pollination services of local bee populations. A loss in bee diversity as a result of exotic plant invasion or revegetation practices which do not adequately restore the flowering plant resources that support pollinators, contributes to habitat fragmentation. Even after successful pollination, developing ovules and maturing seed are subject to predation by insects. Several species of fruit flies (Tephritidae) are host specific to members of the plant family Asteraceae and can cause significant reductions in total seed yields in wild populations. Such losses in seed yield impact a plant's annual contribution to the seed bank. Reductions in seed yield can also impact the potential rewards from harvesting wild seed for use in the reclamation industry. With the heightened interest in using native plants for restoring western rangelands, securing a reliable seed source, whether from wild seed collection or agricultural production, has become increasingly important. Restoring native forbs in degraded rangelands will help restore native bee populations, improve population stability for pollinators, and improve wildlife habitat. This dissertation presents three separate manuscripts that address factors affecting the reproductive success of wild plant populations. All three manuscripts are formatted for publication in professional journals and are included as separate chapters. Chapter 1 examines the impact of cheatgrass and crested wheatgrass habitat on bee diversity compared to sagebrush and pinyon/juniper habitat. It was found that bee diversity is highest in pinyon/juniper habitat and lowest in crested wheatgrass. Chapter 2 examines the impact of seed predation on Wyethia amplexicaulis (Nutt.) Nutt. by the fruit flies Neotephritis finalis (Loew) and Trupanea nigricornis (Coquillett) (Diptera: Tephritidae). On average, seed damage was estimated at 38.9%. Chapter 3 examines the impact of seed predation on Agoseris glauca (Pursh) Raf. and Crepis acuminata Nutt. by the fruit fly Campiglossa sp. (Diptera: Tephritidae) and the moth Phycitodes albatella subsp. mucidella (Ragonot) (Lepidoptera: Pyaralidae). Treatment of plants with the pesticide imidacloprid was also investigated and found to provide significantly increase seed yield.