Competition, herbivory, and seed dynamics in native and invasive irises

Biological invasions by exotic species occur worldwide and are recognized as destructive, leading to biodiversity loss and alteration of community and ecosystem processes. Numerous theories attempt to explain how non-native species establish and succeed in their newly introduced ranges. This study investigates the potential invasive success of one exotic, Iris pseudacorus and its ability to sexually reproduce and defend itself against native herbivores compared to a native congener, I. hexagona. I. pseudacorus is native to Europe and Asia where it can be found in a wide range of habitats occurring in both fresh and brackish water. Its environmental tolerance and ecosystem preferences are similar to those of I. hexagona, which is native to the Gulf Coast of North America and the Lower Mississippi River Valley. Throughout the majority of North America it has obtained invasive pest status, since its introduction in the 1800s. Regardless, in coastal Louisiana it is frequently planted in horticultural settings. The experimental studies presented here investigate the seed dispersal abilities, germination while floating, seed establishment, fecundity and how it is impacted by competition and salinity, and test the enemy release hypothesis using both the exotic and native iris for comparison. Data from these studies demonstrate that both species are capable of long distance dispersal events due to their extensive seed floatation abilities, moreover the exotic is capable of germinating while floating and establishing into the soil if allowed. Fecundity for both species was negatively impacted by salinity, however the native exhibited significant increases in seed production when grown under intraspeciefic completion. Interspecific competition on the other hand decreased fecundity of both species significantly. Finally we present data refuting the enemy release hypothesis, and a significant preference for an exotic host plant species by a native insect herbivore. Our data provide some explanation to a potential limitation in population expansion, the exotic I. pseudacurus, may be experiencing here in Louisiana. Further our data support previous hypothesis that argue that freshwater populations will thrive in Louisiana while brackish populations will be limited and persist with a minimal threat to native ecosystems.