Invasions by non-native species are common and widespread, but the long-term outcomes of invasions are unclear. Escape from specialized predators and pathogens may initially enable introduced species to outcompete native ones, but the dominance of introduced species may be reversed if the predators or pathogens in their new habitat switch onto them. Alternatively, native pathogens that attack introduced species might spill back, infect co-occurring native species, and exacerbate the impacts of invasions. This project will evaluate the ecological consequences of pathogen accumulation on invasive species to inform general ecological theory on host-pathogen dynamics and improve our understanding of the long-term outcomes of invasions. A field survey will quantify the prevalence and richness of pathogens that accumulate on stiltgrass, Microstegium vimineum, an aggressive and widespread invader of forest understories in the eastern U.S. By employing a broad chronosequence of sites, the study will show the temporal change, geographical extent, and species diversity of pathogens accumulating on an important invasive plant. Inoculation experiments in quarantined greenhouse environments will be used to evaluate the effects of pathogens on the performance of Microstegium and co-occurring native grasses. Together, these results will serve to evaluate the hypotheses that pathogens accumulate on and reduce population growth of invasive species or spill back onto competing native species and indirectly facilitate invasions.
Biological invasions by introduced species are a major environmental problem in the U.S. By providing new information on the factors that promote or inhibit invasions, this project will be of use in land management and restoration efforts. The study species is itself of significant concern in a number of eastern States. Research findings will be disseminated to land managers, the public, and environmental and conservation organizations via a website and publications. In addition, this project will provide experience and training for undergraduate students and a post-doctoral researcher, and research support to an early-career scientist.
Intellectual Merit Emerging infectious diseases represent a growing threat to human health, agriculture, and ecological communities but may also help control invasive species. To gain insight into the processes and consequences of pathogen emergence and accumulation on an invasive species, we sought to identify pathogens infecting the highly problematic non-native grass Microstegium vimineum (stiltgrass) across its invasive range in the eastern United States, identify site attributes correlated with disease presence and severity, and evaluate how disease and herbivores impact the invader and co-occurring native species. We isolated and cultured potential fungal pathogens infecting Microstegium and co-occurring grasses collected from over 80 sites in 18 states across its invasive range in the US. Of the pathogens isolated from Microstegium, we found a surprisingly large number from a fungal genus that includes many crop and turfgrass diseases, and the most commonly isolated pathogen was a previously unknown species. The other pathogens included two recently described species that have only been found infecting Microstegium within the past decade and a second previously undescribed species. Several co-occurring native grass species were also infected with these same pathogens. At each site we also collected data on site characteristics including latitude, longitude, elevation, canopy cover, and Microstegium population age and used these data to identify variables correlated with disease presence and severity. These analyses indicated that older Microstegium populations are most likely to be diseased, suggesting accumulation of pathogens over time. We also experimentally suppressed pathogens with fungicide in a field study and showed that disease has severe negative effects on Microstegium performance and may allow native plants to recover over time. Taken together, these results have important implications regarding the amplification and evolution of existing and novel pathogens on invasive species, in addition to demonstrating that pathogens and other enemies can accumulate over time and potentially mitigate the effects of problematic invaders on native systems in the absence of human intervention. Broader Impacts This project has provided training and professional development opportunities for postdoctoral research associate Kerry Bohl Stricker including guidance in research methodologies, data analysis and presentation, mentorship, teaching, and administrative skills. In addition, Dr. Stricker was one of twelve invited speakers at the University of Florida Annual Postdoctoral Research Symposium and gave an invited presentation at the 99th Ecological Society of America Annual Meeting in Sacramento, California. She also attended several career development workshops and taught an undergraduate course in plant ecology. This project also involved six undergraduate student research assistants, including an international student from Brazil and a high school student. Student assistants were trained in laboratory techniques, data collection and entry, image processing, and teamwork skills. Finally, a Research Experiences for Undergraduates (REU) supplement trained a highly promising undergraduate student from an institution with limited research opportunities on research methods, including experimental design, data collection, analysis, and presentation.
