Reproductive success of the Canarian Echium simplex (Boraginaceae) mediated by vertebrates and insects

Abstract

Oceanic island ecosystems favour the appearance of novel interactions as a consequence of their depauperate and disharmonic flora and fauna. We investigated Echium simplex, endemic to the Anaga Biosphere Reserve in NE Tenerife, Canary Islands, belongs to the Canarian bird–flower element. Along two flowering seasons, we studied the breeding system of E. simplex, identified the floral visitors and compared the pollination effectiveness of different animal guilds (insects versus vertebrates) by means of selective exclosures. E. simplex is self-compatible but selfing significantly reduced fruit set. The flowers were visited by five bird species (mostly Phylloscopus canariensis and Serinus canarius, but also Cyanistes teneriffae, Sylvia atricapilla and Sylvia melanocephala), a lizard species (Gallotia galloti) and over a hundred insect species (mainly hymenopterans and coleopterans). Flying insects increased fruit set whereas small flower dwellers (mostly beetles) decreased both fruit and seed set. Vertebrates had a negligible effect on reproductive success. We conclude that although the floral resources provided by E. simplex may be important to some vertebrate species, these do not appear to contribute to increase fitness of the plant, which was more dependent upon flying insects for fruit and seed set. We additionally found that plant reproductive structures are heavily damaged by feral goats, which threaten the maintenance of this Canarian endemic species.