So many visitors and so few pollinators: variation in insect frequency and effe...

• Author(s): Castro, Sílvia ; Loureiro, J. ; Ferrero, Victoria ; Silveira, Paulo ; Navarro, Luis
• Date: 2013
• Persistent ID: http://hdl.handle.net/10316/25678
• Origin: Estudo Geral - Universidade de Coimbra
• Subject(s): Legitimate visitors; Nectar robbing; Plant–animal interactions; Pollination effectiveness; Polygala vayredae; Polygalaceae
• Document Type: Article
• Language: English

Description

Plant–pollinator interactions are one of the most important and variable mutualisms having major implications for plant fitness. The present study evaluates the interactions between an endemic milkwort, Polygala vayredae, and its floral visitors by studying the temporal variability, foraging behaviour and effectiveness of floral visitors in three populations during three consecutive years. The flowers were visited by a diverse array of insects, totalling 24 different species. However, only four species were effective pollinators, depositing pollen on stigmas after one visit, while the remaining species behaved as nectar robbers, secondary nectar robbers or nectar thieves and were completely ineffective for pollination. Among the effective pollinators, two groups with distinct foraging behaviours were observed: the nectar collecting long-tongued bees Bombus pascuorum and Anthophora sp. and the pollen collectors Eucera longicornis and Halictus sp. No significant differences were observed among pollinators in their efficiency in pollen deposition on stigmas, but significant differences were observed in the foraging behaviour between nectarivorous and pollen collectors. Variation in the abundance and assemblage of floral visitors was observed at the temporal scale and among populations, with the effective pollinators being generally scarce. Consequently, the reproductive outcome in this species was low and significantly variable among populations and years. The results highlight the importance of studying floral visitor effectiveness when determining pollinator assemblages. The Portuguese Foundation for Science and Technology financed the work of Sılvia Castro (FCT/BD/10901/2002 and FCT/BPD/41200/2007). Victoria Ferrero was funded by a Xunta de Galicia postdoctoral contract. The work was partially financed under the grants from the Xunta de Galicia (INCITE09-3103009PR), CGL2009- 10466 of the Spanish Direccion General de Investigacion, Ciencia y Tecnologıca (DGICYT) and FEDER funds from the European Union to Luis Navarro.