Assessing the impact of the invasive buff-tailed bumblebee ( Bombus terrestris ) on the pollination of the native Chilean herb Mimulus luteus

The arrival of exotic pollinators to new habitats may introduce new patterns of floral preference and foraging behavior that modify the structure of the resident plant–pollinator community. The aim of this paper is to examine the potential impact of the exotic bumblebee Bombus terrestris on the pollination service provided by the native pollinator assemblage of the herb Mimulus luteus . The study was performed in a high-elevation locality in the Chilean Andes during the summer seasons of 2010, 2011, and 2012. We recorded visitation rate, and the number of pollen grains transported on the body of B. terrestris and native pollinators and the pollen deposition on the stigmas of M. luteus . Pollinator effectiveness (pollen deposited × visitation rate) was compared among species. Results revealed that B. terrestris was an inefficient pollinator, due to the low amount of pollen delivered on stigmas and the low and intermittent visitation rate across years. The parallel inter-annual variation in the visitation rate of B. terrestris and the native bumblebee Bombus dahlbomii suggests that the integration of B. terrestris had no important consequences for the congeneric species. In general, B. terrestris accounted for a low proportion of the pollen transfer in M. luteus , reaching 4.6 % in 2010, absence of effect in 2011, and 0.01 % in 2012. These results suggest that in spite of being a quickly spreading species in Chile, B. terrestris is still in the initial phase of invasion in this area.