| Parasitic plants attach to other plants and obtain water, nutrients, and/or carbon from their vascular systems, causing a variety of effects at the individual, population, and community levels. These effects have been hypothesized to be similar to those of insect herbivores, but few studies have tested this idea. In this study, I investigated the effects of the parasitic plant Cuscuta gronovii on the growth, fitness, and mating system of one of its host plants, Impatiens capensis. I also attempted to compare the effects of the parasite to the effects of insect herbivores, but the herbivory levels in the experiment were too low to make a valid comparison. Plants infested with C. gronovii were 21% shorter than plants that were not infested, produced 27% fewer seeds, and produced a greater proportion of self-pollinated seeds (0.95 compared to 0.84). Instead of comparing their effects to those of all insect herbivores, parasitic plants might more appropriately be compared to other organisms that also act as physiological sinks, such as gall-forming insects and sap-sucking insects. |
