PARENT SESSION
Poster Session # 16: Invasive Species.

Wednesday, August 6 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Differences in survival, traits, and herbivory of seedlings from native and invasive congeners.

Young, Lauren^*,1, Louda, Svata¹, ¹ University of Nebraska, Lincoln, Nebraska

ABSTRACT- Naturalized plants often appear more vigorous in their non-native range. A hypothesized mechanism underlying such increased vigor by plants in the non-native range is reduced herbivore pressure. Under this hypothesis plants in their non-native range are expected to allocate more to growth and biomass (enhanced competitive ability) and less to defense (absence of native enemies). We examined size, frequency of herbivory, and survival of invasive thistle seedlings, Cirsium vulgare, in North America. Seedlings of C. vulgare were grown in the field from seed using seed from exotic and naturalized seed sources. We compared the exotic seedlings to those of a native North American congeneric thistle, Cirsium altissimum. The proportion of seedlings surviving was greatest for the native C. altissimum, followed by C. vulgare from naturalized seeds, and then from exotic seed origin. Native C. altissimum and C. vulgare seedlings of exotic seed origin had greater rosette area than did C. vulgare seedlings of naturalized seed. Unexpectedly, C. vulgare seedlings from naturalized seed were more frequently damaged by July, than were those of C. altissimum, the native thistle. The greater survival of C. vulgare seedlings from naturalized seed than from exotic seed is consistent with the hypothesis of potential adaptive change in this weed. Additionally, the greater frequency of herbivore feeding on Cirsium vulgare seedlings from naturalized seed than the native C. altissimum suggests that native herbivores could be providing resistance to invasive spread by C. vulgare in tallgrass prairie areas of eastern Nebraska.

Key words: Cirsium, seedlings, insect herbivory, thistles