CONSEQUENCES OF PLANT-POLLINATOR AND FLORAL-HERBIVORE INTERACTIONS ON THE REPRODUCTIVE SUCCESS OF THE CANARY ISLANDS ENDEMIC CANARINA CANARIENSIS (CAMPANULACEAE)

Premise of the study: Pollination is a critical phase for plant reproduction, but ecological and evolutionary outcomes by pollinators may be counteracted by floral herbivores. These interacting assemblages may also be altered (directly or indirectly) by introduced species, especially on oceanic islands. In this study, we analyzed the effects of opportunistic nectar-feeding passerine birds and native (semi-slugs) and introduced (rats) floral herbivores on the reproductive success of Canarina canariensis. Methods: Manual pollination experiments were conducted to determine plant breeding system and pollen limitation. We also identified floral visitors and their visitation frequencies by censuses. Bird pollination effectiveness was evaluated by selective exclosures. The intensity of floral herbivory by native vs. introduced herbivores and its effect on plant fitness was estimated in different areas within the Canary island of Tenerife. Key results: Canarina canariensis had a very low spontaneous selfing ability and high pollen limitation, despite being self-compatible. Birds increased fruit set and the percentage of viable seeds per fruit, while florivores, the principal floral visitors, reduced them. Semi-slugs mainly consumed male reproductive organs, while rats preferred female. There was a strong within-island spatial variation in the herbivory intensity. Conclusions: Opportunistic nectar-feeding birds increase the production of viable seeds in C. canariensis, but their beneficial effects are counteracted by the high incidence of floral herbivory. Because native semi-slugs damaged anthers more frequently than did introduced rats, these florivores may differ in their effects on male and female plant reproductive success.