PARENT SESSION
Friday, August 11, 8:00-11:30 am
COS 104 - Invasive species VII: prevention, control, and models
Ballroom E, Ballroom Level, Cook Convention Center
Presiders: T Langkilde

Impact of enemy release on population growth in Lespedeza.

Schutzenhofer, Michele^*,1, Knight, Tiffany², ¹ Saint Louis University, St. Louis, MO² Washington University, St. Louis, MO

ABSTRACT- The enemy release hypothesis (ERH) posits that exotic plants experience decreased regulation by herbivory, allowing them to achieve high population sizes. Previous studies of the ERH have yielded conflicting results as to the validity of this hypothesis as a mechanism to explain the success of invasive species. However, few studies have examined the effects of herbivory on fitness and its impact on population dynamics. In this study, vital rates of two co-occurring species, exotic Lespedeza cuneata and native L. virginica, were examined under ambient, reduced, and increased (simulated) herbivory. Results support the ERH; exotic L. cuneata experienced lower ambient levels of herbivory than native L. virginica and plant fitness (fecundity) was correlated with the incidence of herbivory. The effects of simulated herbivory on plant fitness differed between these species. Native L. virginica was more strongly affected by simulated increased herbivory than exotic L.cuneata. Lespedeza cuneata's seed production was not affected until 80% simulated increased herbivory, suggesting that although fitness is affected by herbivory, these individuals are able to tolerate high levels of damage. Projection matrix modeling indicates that the vigor of the exotic species relative to its native counterpart is due to factors other than herbivory. We suggest that biological control alone will not be sufficient to curb the invasion of L. cuneata.

Key words: invasive species, Lespedeza, mesic