Pollinator Sharing in Specialized Bee Pollination Systems: a Test with the Synchronopatric Lip Flowers of Centrosema Benth (Fabaceae)

Mauro Ramalho, Maise Silva, Gilson Carvalho
2014 Sociobiology  
Bee-pollinated lip flowers of two synchronopatric species of Centrosema were used as models to examine the influence of specialized pollination systems on the ecological mechanisms of pollinator sharing. Regression analysis of bee abundances in the habitat on bee abundances on C. pubescens flowers was significant (r = 0.69; P = 0.001) and became very consistent and highly significant (r = 0.87; P = 0.00001) using a size threshold of bee pollinators longer than 15mm. These same relationships
more » ... e relationships were not significant (P > 0.01), however, for C. brasilianum flowers. The structures of the two pollination systems also sustained the hypothesis of a size threshold for pollinators, although only the C. pubescens-bees interactions sustained the hypothesis of random interactions proportional to species abundances in the habitat. The flower visitor pools of the two plant species shared the same four main bee guilds: the pollinators Centridini, Xylocopa, and Euglossini and the primary nectar robber Oxaea. However, a significant divergence (P < 0.01) was detected between the two systems when the abundances and behaviors (pollinators or cheaters) of the main shared flower visitors were incorporated into the overall quantitative analysis (NMDS). The flowers size differences are not significant (P > 0.05) and could not explain these divergences. Particularly, the concentrations of the largest pollinators Eulaema and Xylocopa on C. pubescens flowers and the behavior shift of Centridini bees that act as legitimate pollinators in C. pubescens and as nectar robbers in C. brasilianum are better understood as functional foraging responses triggered by the synchronopatry and by nectar volume differences (P = 0.001) between both lip flowers. Paradoxically, the robbery activity of Centridini bees arises as a supply side effect of smaller nectar volume in C. brasilianum flowers. (2009) concluded that the "pollination syndrome hypothesis", as traditionally stated, did not properly describe the diversity of floral phenotypes and only poorly predicted plant species pollinators. These authors therefore recommended a 'fresh look at how the traits of flowers and pollinators relate to visitation and pollen transfer' in searching for appropriate descriptions of functional floral diversity. A question central to this debate is if other variables can be as important as morphological restrictions in structuring pollination systems. Recent analyses of partnerships and the structures of flower-visitor webs have both indicated that morphological constraints continue to play a central role in the general theory of the organization of pollination systems. RESEARCH ARTICLE -BEES
doi:10.13102/sociobiology.v61i2.189-197 fatcat:6bw3wgu7jfa67itde2cfexcqnu