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

Shifts in flowering phenology in response to spring temperatures in eastern Tennessee

Plant phenological shifts are among the clearest indicators of the effects of climate change. In North America, numerous studies in New England have demonstrated earlier spring flowering compared to historical records. However, few studies have examined phenological shifts in the southeastern United States, a highly biodiverse region of North America characterized by dramatic variation in abiotic conditions over small geographic areas. Here, we use 1000+ digitized herbarium records along with location-specific temperature data to examine phenological shifts of 14 spring-flowering species in two adjacent ecoregions in eastern Tennessee. We show that spring-flowering plant communities in the Blue Ridge and Ridge & Valley ecoregions differ in their sensitivity to temperature; plants in the Ridge & Valley flower 2.7 days earlier/ºC on average compared to 1.3 days/ºC for plants in the Blue Ridge. Additionally, we show that for the majority of species in both ecoregions, flowering is sensitive to spring temperature; i.e., in warmer years, most species flowered earlier. Despite this sensitivity, we did not find support for community-level shifts in flowering within eastern Tennessee in recent decades, likely because increases in annual temperature in the southeast are driven primarily by warming summer (rather than spring) temperatures. These results highlight the importance of including ecoregion as a predictor in phenological models for capturing variation in sensitivity among populations and suggest that even small shifts in temperature can have dramatic effects on phenology in response to climate in the southeastern United States.See README.md for descriptions of data structures and sharing/access information