Floral trait similarity and pollinator sharing between native and alien plants mediate heterospecific pollen transfer with consequences for pollination success

Abstract Heterospecific pollen transfer (HPT) is ubiquitous in co-flowering communities with strong implications for pollination success. Heterospecific pollen transfer may be especially relevant in invaded plant communities. The mechanisms mediating HPT in invaded communities however remain poorly understood even though it could help better understand the outcome of plant invasions. In this study, we use structural equation modeling to evaluate the role of floral trait similarity and pollinator sharing in HPT and pollination success of native plants in invaded coastal communities. Our results show that increased pollinator sharing between native and alien plants reduces total pollen loads on floral stigmas. In turn, an increase in total pollen load reduced proportion of heterospecific pollen (HP) but increased heterospecific pollen richness and the proportion of alien pollen (HPR and AHP respectively). The model showed that pollination success (i.e., proportion of pollen tubes) decreased with an increase in AHP but increased with increasing total HP. Unexpectedly, our results showed that floral trait similarity did not explain the degree of pollinator sharing. However, the proposed model suggested that increases in floral trait similarity and pollinator sharing negatively affect native pollination success. Our results also showed that increased pollinator sharing between native and alien plants increases pollination success, suggesting a facilitative effect of alien on native plants. Overall, our results highlight the importance of considering floral trait similarity and pollinator sharing in mediating the complex dynamic of HP transfer between native and alien plants and its consequences on native pollination success with implications for plant invasion success.