The enemy release hypothesis often is invoked to explain the success of exotic species in new geographical regions. I hypothesized that escape from natural enemies is not limited to the introduced range of a species but may operate on a local scale within the native range. I tested this using an invasive North American native plant (Ambrosia artemisiifolia) or Common Ragweed.
I found evidence of enemy release from herbivorous and granivorous insects, but no effects on plant performance. The soil community had a net positive effect on the growth of ragweed regardless of habitat; however this effect attenuates over time. Ragweed seeds had higher germination rates in old fields than existing ragweed populations, but not because of fungal activity. My results demonstrate that plants can escape natural enemies in their native habitat, but this doesn't necessarily translate to increased individual plant performance.