Reward quality predicts effects of bird-pollinators on the reproduction of African Protea shrubs

Published Date

20 May 2015, Vol.17(3):209–217, doi:10.1016/j.ppees.2015.02.007

Research article

Title 

Reward quality predicts effects of bird-pollinators on the reproduction of African Protea shrubs

• Author 

• B. Schmid ^a,b,,,
• H. Nottebrock ^b,c,d
• K.J. Esler ^b
• J. Pagel ^c,d
• A. Pauw ^e
• K. Böhning-Gaese^a,f
• F.M. Schurr ^c,d
• M. Schleuning ^a

• aSenckenberg Biodiversity and Climate Research Centre (BiK-F), Senckenberganlage 25, 60325 Frankfurt am Main, Germany
• bDepartment of Conservation Biology and Entomology and Centre for Invasion Biology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa
• cInstitute of Landscape and Plant Ecology, University of Hohenheim, August-von-Hartmann-Str. 3, 70599 Stuttgart, Germany
• dInstitut des Sciences de l’Evolution, UMR 5554, Université Montpellier 2, Place Eugène Bataillon, F-34095 Montpellier Cedex 05, France
• eDepartment of Botany and Zoology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa
• fDepartment of Biological Sciences, Johann Wolfgang Goethe-University, Max-von-Laue-Straße 9, 60438 Frankfurt am Main, Germany

Received 1 July 2014. Revised 12 December 2014. Accepted 19 February 2015. Available online 6 March 2015.

Highlights

• •
  Protea species of the Cape Floristic Region are self-compatible.
• •
  Putative ornithophilous Protea species vary in the dependence on avian pollination.
• •
  Floral rewards are associated with the effects of avian pollinators on reproduction.

Abstract

Pollination syndromes predict the principal animal pollinators of plant species from floral traits. However, the existence of discrete pollination syndromes and the relevance of these syndromes for the effects of animal pollinators on plant reproduction are controversial and a quantitative, trait-based approach may refine the concept of pollination syndromes. Thus far, however, very few studies have simultaneously analysed the importance of signalling, accessibility and reward traits of flowers for the effects of animal pollinators on plant reproduction of multiple species. The genus Protea is an ideal study system because the members of this genus exhibit remarkable variation in functional traits and Protea species are visited by several guilds of animal pollinators, such as birds and insects. We experimentally investigated seven Protea species from the South African fynbos to assess variability in reproduction (seed set, seed mass, germination) in response to pollinator exclusion (full-exclusion, bird-exclusion) and hand-pollination (self-pollen, cross-pollen). To generalise the findings of the experiment, we conducted a meta-analysis of the effects of bird-exclusion on seed set of 14 Protea species, associating effect sizes of bird-pollination with signalling (inflorescence length and diameter), accessibility (inflorescence and style length) and reward traits (length of pollen presenter, nectar volume and sugar concentration). All Protea species were self-compatible, but only two species were to a small degree capable of autonomous selfing. Protea species varied in their dependence on animal pollinators, including species depending exclusively on birds, insects, or both for seed production. Protea species exhibited continuous variation in the effects of bird-pollinators on reproduction, challenging the accuracy of categorical pollination syndromes for predicting pollinator effects on plant reproduction. The meta-analysis showed that the quality of floral rewards, especially nectar sugar concentration, predicts the dependence of Proteareproduction on bird pollinators, whereas the signalling and accessibility traits tested in this study were not important. Beyond revealing new insights into the pollination biology of Protea species, our findings underscore the usefulness of experimental approaches on multiple plant species to test the effects of pollinator guilds on plant reproduction and contribute to a trait-based understanding of the functional determinants of plant–pollinator interactions.

Keywords

• Pollination syndrome
• Bird pollination
• Floral traits
• Nectar sugar concentration
• Proteaceae
• Cape Floristic Region

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  Corresponding author at: Senckenberg Biodiversity and Climate Research Centre (BiK-F), Senckenberganlage 25, 60325 Frankfurt am Main, Germany. Tel.: +49 6975421821; fax: +49 6975421800.

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