| Invasive species can cause significant ecological harm and are economically costly to manage. Therefore, it is essential to investigate the nature of invasive species' success. Here, I examine the effects of herbivory on the mating system, fitness, and population growth rate of Lespedeza cuneata, a noxious invader in the Midwest. Specifically, I use congeneric comparisons to investigate herbivory's impact on plant mating system and the role of enemy release and tolerance to herbivory as potential mechanisms for L. cuneata's success. Furthermore, I use population modeling to evaluate if biocontrol is a feasible management option. My results indicate that enemy release impacts the fitness of L. cuneata: the invasive was found to experience lower ambient levels of herbivory than its native congener, L. virginica, and plant fitness was impacted by herbivory: under lower levels of herbivory, both species produced a greater proportion of CH seed, which have greater fitness than CL seed. However, while enemy release partially contributes to the fitness of L. cuneata, I found that it contributes very little its population growth rate. Indeed, even under 80% additional herbivory, L. cuneata has a population growth rate of 24.2, which indicates that biological control via a leaf-chewing herbivore would be an unsuccessful management option. This tolerance to herbivory is not unique to L. cuneata, as I found that both L. cuneata and L. virginica exhibit high tolerance to herbivory. Population growth rates within each species were not significantly different under control and 80% increased herbivory. Therefore tolerance is a trait shared within the genus and subsequently does not serve as a unique trait to facilitate L. cuneata's success. Thus high seed set, enemy release, and high levels of tolerance help to explain the success of L. cuneata. Future work should use further comparative analyses within the genus to investigate causes of rarity and invasiveness. |
