Geographic distribution and trait-mediated causes of nectar robbing by the European bumblebee Bombus terrestris on the Patagonian shrub Fuchsia magellanica

- Invasive floral visitors can disrupt mutualistic networks exerting nectar robbing.
- Phenotypic traits of flowers and animals trigger nectar robbing.
- Phenotypic traits and nectar robbing do not vary gradually in the geographic context.

Invasive floral visitors may obtain nectar rewards from native plants exerting nectar robbing. Nevertheless, the probability of a plant to be robbed will ultimately depend upon the accessibility constraints imposed by the phenotypes of flowers and animals, and putatively upon the abundance of animals. The alien bumblebee B. terrestris is widely distributed in the temperate forests of Chile, where it is exerting nectar robbing on flowers of F. magellanica. Its geographic distribution and the causes of nectar robbing, however, are currently unknown. The aim of this study is to evaluate the distribution of nectar robbing in a wide range of distribution of plants and animals, and the causes of nectar robbing in terms of floral and animal phenotypes, and in terms of animal abundances. The primary nectar robbing did not correlate with the latitude, longitude or altitude of populations, thus indicating an absence of cline variation in the causes of nectar robbing. The variability of primary nectar robbing seemingly showed a bimodal distribution, since the most represented categories were the low and high incidence of primary nectar robbing. Petal length, rather than other flora traits, coupled to the glossa length of animals, played a pivotal role in the probability of flowers to experience nectar robbing. The putative negative consequences upon the population persistence and the evolution and maintenance of floral phenotypes of hummingbird-pollinated plants strongly encourage new assessments.