They studied invaded plant communities across Europe, observing pollinator visits to flowers in multiple 50 x 50 m plots. They calculated connectance as the number of interactions standardized by network size. They showed that exotics fully integrated into plant-pollinator networks. Exotic species accounted for 42% of all pollinator visits and 24% of all network connections -a testament to the overall abundance of exotics in many communities. However, these exotics did not affect overall changes in network connectedness, revealing that these networks are quite robust to invasions.
That said, researchers must now ask if this is true in networks that do contain high numbers of specialists (e.g., orchids) or if the relative few specialists in generalist-dominated systems are more susceptible to changes from exotics.
Vila, M., Bartomeus, I., Dietzsch, A., Petanidou, T., Steffan-Dewenter, I., Stout, J., & Tscheulin, T. (2009). Invasive plant integration into native plant-pollinator networks across Europe Proceedings of the Royal Society B: Biological Sciences, 276 (1674), 3887-3893 DOI: 10.1098/rspb.2009.1076