PARENT SESSION
Oral Session # 37: Invasive Species III: Grasses and Shrubs.
Presiding: C Lortie
Tuesday, August 5. 1:30 PM to 5:00 PM, SITCC Meeting Room 205.
Plant community composition and natural enemies affect invasion success of a grassland plant.
Howe, Katherine*,1, 1 SUNY-Stony Brook, Stony Brook, NY
ABSTRACT- Biological invasions are a leading threat to biodiversity, yet we still know little about what makes some species successful invaders. Two factors believed to improve invader success are reduced damage from predators or pathogens on exotic species relative to native species and superior competitive ability of invaders compared to native species. I examined the role of both of these factors in affecting the success of a grassland forb introduced from Eurasia, Hieracium aurantiacum, and its co-occurring, native congener, Hieracium longipilum. I tested the effects of natural enemies on both species by experimentally excluding herbivores and pathogens from plots planted with both species. I also examined the effects of neighboring plant community composition and edaphic properties on the success of both species. In all years from 1999-2002, both species showed increased growth when insect herbivores were experimentally excluded, and neither species showed a significant response to the exclusion of foliar fungal pathogens. The native species had increased flower number and taller flowering stalks in plots where deer were excluded, but there was no effect of deer exclusion on the exotic species. Success of both species was also related to the composition of the surrounding plant community. H. longipilum achieved larger sizes in areas with greater cover of legumes, graminoids, and leaf litter, while H. aurantiacum size was negatively correlated to percent cover of legumes and leaf litter. H. longipilum size appeared to be unrelated to soil characteristics, but H. aurantiacum individuals were smaller in areas with higher levels of soil moisture. The results of this study suggest that although H. aurantiacum appears to have an advantage over the native species resulting from lower rates of herbivory, its invasion is likely to be limited to areas with suitable soil characteristics and plant community composition.
Key words: natural enemies, community composition, invasive species, grassland