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So many visitors and so few pollinators: variation in insect frequency and effectiveness governs the reproductive success of an endemic milkwort

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Abstract

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.

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Acknowledgments

Authors thank the Departamento de Medi Ambient of Generalitat de Cataluña and the Consorsi d’Alta Garrotxa for allowing this research and to Parc Natural de la Zona Volcànica de la Garrotxa for all the support during field seasons. Authors are grateful to Irina Stanescu for the assistance during 2006 field season and to José M. Gómez for the invaluable help with data analysis and comments during manuscript preparation. Authors are also grateful to the Associate Editor and two anonymous reviewers for the helpful comments to the manuscript. The Portuguese Foundation for Science and Technology financed the work of Sílvia 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 Dirección General de Investigación, Ciencia y Tecnologíca (DGICYT) and FEDER funds from the European Union to Luis Navarro.

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Author notes

  1. Sílvia Castro

    Present address: Department of Life Sciences, Centre for Functional Ecology (CFE), University of Coimbra, PO Box 3046, 3001-401, Coimbra, Portugal

Authors and Affiliations

  1. Department of Life Sciences, Centre for Functional Ecology (CFE), University of Coimbra, PO Box 3046, 3001-401, Coimbra, Portugal

    João Loureiro & Victoria Ferrero

  2. Department of Plant Biology and Soil Sciences, Faculty of Biology, University of Vigo, As Lagoas-Marcosende, 36200, Vigo, Spain

    Victoria Ferrero & Luis Navarro

  3. Department of Biology, CESAM, University of Aveiro, Campus Universitário de Santiago, 3810-193, Aveiro, Portugal

    Paulo Silveira

Authors
  1. Sílvia Castro
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  2. João Loureiro
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  3. Victoria Ferrero
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  4. Paulo Silveira
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  5. Luis Navarro
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Corresponding author

Correspondence to Sílvia Castro.

Appendix 1

Appendix 1

See Table 5.

Table 5 Number of interactions between P. vayredae and its floral visitors in the three populations studied during 2005, 2006 and 2007
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Castro, S., Loureiro, J., Ferrero, V. et al. So many visitors and so few pollinators: variation in insect frequency and effectiveness governs the reproductive success of an endemic milkwort. Plant Ecol 214, 1233–1245 (2013). https://doi.org/10.1007/s11258-013-0247-1

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