Predicting multi-trophic consequences of an emerging disease

In the southeastern US, laurel wilt disease (LWD) is impacting numerous species in the Lauraceae family, with the majority of cases observed on Persea borbonia, a common sub-canopy tree found in many Coastal Plain habitats. This species is also known to be the primary larval host of the palamedes swallowtail (Papilio palamedes). The exotic Cinnamomum camphora is the only Lauraceae species that has shown resistance to LWD and could benefit from opportunities to replace P. borbonia and other Lauraceae species threatened by LWD. The primary objectives of this study were four fold: 1) to quantify P. borbonia sprouting responses in the field and greenhouse and determine the effect of P. borbonia removal on the composition and abundance of woody and herbaceous plant species in the understory layer, 2) to test the relative suitability of C. camphora as an alternative larval host for P. palamedes, 3) to determine the reliance of the Platanthera ciliaris on P. palamedes for successful pollination and the relative availability of alternative long-tongued pollinators, and 4) to forecast how disease-induced shifts in the relative abundance of native (P. borbonia) and exotic (C. camphora) fruit may alter patterns of consumption and subsequent dispersal of C. camphora by birds. The field component (Grand Bay National Estuarine Research Reserve (GBNERR), Jackson County, MS) of chapter two involved the removal of P. borbonia main stems to mimic the impacts of LWD which resulted in a significant increase (∼50%) in light transmission. All treated individuals produced sprouts and the size and number of sprouts was positively related to initial tree size. Following the removal of P. borbonia from treatment plots, Ilex vomitoria showed the greatest increase in basal area after two years. Both woody seedlings and herbaceous plants showed no significant trends in composition and/or abundance over time. In the greenhouse (Southern Illinois University, Carbondale, IL), the stem and leaf biomass of vegetative sprouts was significantly greater in a high-nutrient treatment. Light treatments had no effect on sprout production. Results from chapter two suggest that the loss of P. borbonia from the canopy layer may have little direct effect on plant community dynamics. In chapter three, I used laboratory experiments and field observations to compare larval performance and adult female preference of P. palamedes between C. camphora and P. borbonia foliage. In chapter four, I monitored pollinator visitation and measured nectar spur lengths of P. ciliaris flowers and proboscis lengths of its floral visitors (at GBNERR). In chapter five, I investigated redundancy between C. camphora and P. borbonia with respect to fruit characteristics (physical and chemical) and selectivity by frugivorous birds (at GBNERR). Combined, the chapters of this dissertation present substantial empirical evidence for the potential multi-trophic level impacts of an exotic plant disease. While it remains unclear how dramatic these impacts will be, the approach used here is vital for understanding and mitigating the long-term ecological effects of species/disease invasions. (Abstract shortened by UMI.).