My 5-chapter dissertation research focuses on the conservation of Ivesia webberi A. Gray, a U.S. federally threatened forb narrowly distributed in the western Great Basin Desert, along the eastern foothills of the Sierra Nevada. Managing this and many other threatened and endemic taxa in the region severely impacted by human disturbance, fire regime alterations, and invasion by nonnative plant species requires an understanding of the species biology, ecological interactions, seed regeneration potentials, and accurate estimation of species distribution, and the ability to evolve in a changing environment and climate. My research dissertation addressed these questions, and the key findings are published in peer-reviewed scientific journals. My research was funded by the U.S Fish and Wildlife Service, with supplemental funding support from the private sector, native plant societies in California, Nevada, Oregon, Utah, Idaho, and Arizona, as well as the Society for Conservation Biology, and Northern California Botanists. You can read the entire dissertation here.
Genetic diversity, population structure, and functional connectivity
Using microsatellite DNA markers, I investigated population structure, rates and direction of gene flow, genetic diversity, and effective population sizes among Ivesia webberi populations. I also tested the predictions of isolation by geographic distance, landscape resistance, and environmental heterogeneity on genetic structure. The results show contemporary gene flow among the populations which reduced with geographical distance, moderate genetic diversity, and genetic structure patterned along isolations by distance and environment. However, marginal populations are genetically isolated, and exhibit higher relatedness and lower genetic diversity. The paper is published in Ecology and Evolution.
Iterative ecological niche modeling and model-guided field sampling resulted in the discovery of new locations of Ivesia webberi
Niche models were fitted using weighted ensemble forecasting of six modeling algorithms. Iterative models were fitted from 2015 to 2020, simultaneously with field validation surveys to the projected suitable areas. Nine new locations were discovered, and the environmental conditions in these new locations resulted in a 7% expansion of the ecological niche of I. webberi. This paper was recently accepted for publication in Endangered Species Research
Relationship between aboveground flora and the soil seed bank in the Great Basin Desert
Floristic similarity between the aboveground flora and the soil seed bank in sites harboring Ivesia webberi were investigated and quantified. Findings illustrate a significant dominance of the invasive annual grasses in the soil seed bank, which may signify a reducing ecological resilience of these plant communities. Furthermore, post-disturbance early succession may be dominated by alien weeds. Read more about this in the published paper
Ivesia webberi seed viability and germination
Effective seed banking and ecological restoration requires an understanding of seed biology of native plants. This study investigated seed viability loss in Ivesia webberi over storage time, relationship between seed size and viability, and the accuracy of multispectral and seed x-ray imaging vs tetrazolium tests in predicting viability of I. webberi seeds. Furthermore, 68 germination experiments were conducted to investigate optimal dormancy release and germination in I. webberi seeds. We show that seed viability tests in I. webberi could be estimated accurately using seed x-ray or multispectral imaging. Optimal seed germination was observed using cold stratification, and growth hormones. The effect of treatments on I. webberi seed germination is currently being modeled using regression methods, mixed models, relative light germination percentage, and random forest models.
Genome size and ploidy in Ivesia
Knowledge is lacking on the size of nuclear DNA content (= genome size) of Ivesia taxa, and the ploidy level/ chromosome numbers in some of the taxa. This study estimated genome size in 31 of 38 taxa in Ivesia, as well as intraspecific genome size variations in I. webberi. Findings showed that all sampled Ivesia taxa are diploid with 28 chromosomes. Variations in genome size variations among I. webberi populations are geographically structured, following the predictions of the central-marginal hypothesis. This also raises the possibility of gene flow playing a role in the genome size variations. Following the predictions of the nucleotype theory, genome size across all I. webberi taxa show a significant positive relationship with actual evapotranspiration and seed size. This study is accepted for publication in Western North America Naturalist journal.
