| With little previous research on Astragalus peckii (Fabaceae), a state-listed Threatened species in Oregon, I investigated three facets of its biology which are integral to the conservation and management of the species. First, a four-year demographic study of two large populations revealed increasing population growth at one site (Chiloquin) and stable to declining population growth at another (Bull Flat). Both sites had varying levels of herbivory from a microlepidopteran larva, Sparganothis tunicana . Herbivore damage, regardless of when it occurred during the plant growing season, was correlated with increased plant mortality at Bull Flat but not Chiloquin. At Chiloquin, greater moth damage was correlated with decreased reproduction, particularly when the moth was active earlier in the growing season. These reductions in plant vital rates did not appear to contribute to negative population growth at either site. Rather, below-average precipitation levels during the growing season could be correlated with periods of population decline.;From a series of experiments on the reproductive biology of A. peckii, fruit and seed set were generally not limited by the quantity of pollen delivered by pollinators. Instead, high levels of seed abortion prevented most ovules from fully developing to seed. Quality of pollen (self-versus cross-pollen) also did not limit reproduction under natural pollination levels, but self-pollen reduced seed set, and to a lesser degree fruit set, during one of two years of hand-pollination experiments. Possible explanations for the treatment effect, including procedural causes, are discussed. Significant inbreeding depression was evident in the growth of greenhouse-grown seedlings but no statistical differences were found for seed germination or seedling survival. In order to minimize inbreeding depression in the field, adequate sizes of plant and pollinator populations need to be maintained.;Finally, using vegetation, habitat, climate, and soil data in a habitat model, greater A. peckii abundance was correlated with patches of low litter and soil crust cover within sites. Supporting these model results, greenhouse-grown seedlings with 1 cm of juniper litter on the soil surface had lower survival than those grown with less or no litter. There were no strong vegetation associations for A. peckii, though, indicating that within its restricted geographical range, A. peckii can be found in a diversity of plant habitats that have low litter cover. |
