Nectar robbing by the invasive bumblebee <i>Bombus terrestris</i> (Apidae) changes the behavior of native flower visitors of <i>Fuchsia magellanica</i> Lam. (Onagraceae) but not seed set

Mutualisms between plants and pollinators may be threatened by nectar robbers, as these animals typically consume nectar without providing the essential pollination service. In the temperate forests of Chile, the shrub <i>Fuchsia magellanica</i> is primarily pollinated by the hummingbird <i>Sephanoides sephaniodes</i> and the native bumblebee <i>Bombus dahlbomii</i>. However, some populations are also affected by nectar robbing from the invasive bumblebee <i>Bombus terrestris</i>. In a study evaluating 24 populations of <i>F. magellanica</i>, we assessed the effects of nectar robbing on nectar production, the foraging behavior of key pollinators, and the reproductive success of the plant. We measured the nectar production rate and standing crop in flowers that were either protected from visitors or exposed to them. We also observed flower visitation, the foraging behavior of pollinators, and seed sets in experimentally manipulated flowers. Results indicated that nectar robbing reduced nectar production rates by a factor of 4, and the standing crop of nectar by 2.9 times. With an increased percentage of flowers pierced by <i>B. terrestris</i>, the hummingbird <i>S. sephaniodes</i> appeared to reduce its pollinating visits, while <i>B. terrestris</i> increased its robbing visits. Despite these changes in pollinator behavior, there was no significant effect on the seed set. Ultimately, our findings suggest that for <i>F. magellanica</i>, <i>B. terrestris</i> does not pose a significant threat to reproduction, despite its disruptive impact on pollinator behavior.