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Quantity and quality components of effectiveness in insular pollinator assemblages


Ecologically isolated habitats (e.g., oceanic islands) favor the appearance of small assemblages of pollinators, generally characterized by highly contrasted life modes (e.g., birds, lizards), and opportunistic nectar-feeding behavior. Different life modes should promote a low functional equivalence among pollinators, while opportunistic nectar feeding would lead to reduced and unpredictable pollination effectiveness (PE) compared to more specialized nectarivores. Dissecting the quantity (QNC) and quality (QLC) components of PE, we studied the opportunistic bird–lizard pollinator assemblage of Isoplexis canariensis from the Canary Islands to experimentally evaluate these potential characteristics. Birds and lizards showed different positions in the PE landscape, highlighting their low functional equivalence. Birds were more efficient than lizards due to higher visitation frequency (QNC). Adult lizards differed from juveniles in effecting a higher production of viable seeds (QLC). The disparate life modes of birds and lizards resulted in ample intra- and inter-specific PE variance. The main sources of PE variance were visitation frequency (both lizards and birds), number of flowers probed (lizards) and proportion of viable seeds resulting from a single visit (birds). The non-coincident locations of birds and lizards on the PE landscape indicate potential constraints for effectiveness. Variations in pollinator abundance can result in major effectiveness shifts only if QLC is relatively high, while changes in QLC would increase PE substantially only at high QNC. The low functional equivalence of impoverished, highly contrasted pollinator assemblages may be an early diagnostic signal for pollinator extinction potentially driving the collapse of mutualistic services.

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The authors thank especially A. M. Rodríguez and D. Rodríguez, R. Pedrianes, M. Carrión and the forest guards of Teno Rural Park for their technical support. The Island Ecology and Biogeography Research Group (La Laguna University), Anna Traveset and the Terrestrial Ecology Group (IMEDEA-CSIC) and the city council of Buenavista del Norte helped with logistics. Sampling permits were granted by the Department of Sustainability, Territory and Environment of the Cabildo Insular de Tenerife. Jens M. Olesen provided us generously with the images of the pollinators P. canariensis and G. galloti visiting the flowers of I. canariensis (Online Resource 1). Comments by Eugene W. Schupp, Steven D. Johnson and two anonymous referees greatly improved the manuscript. The study was supported by a predoctoral fellowship to M. C. R. from the Consejo Superior de Investigaciones Científicas (I3P I3PPRE_06_00019 CSIC), a postdoctoral grant to A. V. from the Ministerio de Ciencia e Innovación (RYC-2007-00620), and funds to P. J. from the Junta de Andalucía (Excellence grants P07-RNM0284, RNM-573). The experiments performed in this study comply with the current Spanish laws.

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Correspondence to María C. Rodríguez-Rodríguez.

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Communicated by Steven Johnson.

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Rodríguez-Rodríguez, M.C., Jordano, P. & Valido, A. Quantity and quality components of effectiveness in insular pollinator assemblages. Oecologia 173, 179–190 (2013).

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  • Bird pollination
  • Canary Islands
  • Lizard pollination
  • Opportunistic nectar-feeding
  • Plant reproductive biology