Impacts of anthropogenic change on plant reproduction and fitness

Humans are altering natural systems around the globe in myriad ways. For plant species, such anthropogenic changes have resulted in increasingly fragmented populations, desynchronized interactions with mutualists, and shifted geographic ranges, among other effects. However, despite numerous examples of human impacts on plant populations, the consequences of these changes on plant reproduction remain poorly understood. In my thesis, I investigate the impacts of two forms of anthropogenic change–habitat disturbance and climate warming–on plant reproduction and fitness. I take two distinct approaches to address questions posed at local and regional scales. In Chapter I, I ask how inbreeding depression varies across the life cycle of the critically imperiled California endemic species, Collinsia corymbosa (Plantaginaceae). I show that, consistent with other primarily outcrossing species, inbreeding depression in C. corymbosa is most pronounced late in life history, specifically during the female reproductive phase of the life cycle. Inbred plants demonstrated significantly lower rates of autonomous autogamy (δ [delta] = 0.448) and flower production (δ [delta] = 0.225), limiting the ability of this species to set seed in the absence of pollinators. In Chapter II, I ask whether flowering and fruiting dates have advanced for 14 spring-flowering plant species in the Blue Ridge and Ridge & Valley ecoregions of eastern Tennessee over the past century. Additionally, I investigate how phenological sensitivity to spring temperature varies between ecoregions. Utilizing phenological observations sourced from 1000+ digitized herbarium specimens, I show that the sensitivity of flowering phenology to spring temperature at the community level varies between the Ridge & Valley and Blue Ridge (2.7 and 1.3 days earlier per degree Celsius warming, respectively). Further, I show that, while the flowering phenology of the majority of species investigated is sensitive to spring temperature in both ecoregions, flowering and fruiting dates have not significantly advanced in recent decades. Overall, I found variation in plant reproductive responses to anthropogenic change at the maternal family, population, species, community, and regional levels. Together, my research demonstrates that assessing reproduction and fitness at these multiple scales provides nuanced insights into the adaptive capacity and ultimate persistence of species in the Anthropocene.