Differential effects of nectar robbing by the same bumble-bee species on three sympatric Corydalis species with varied mating systems

Abstract

• Background and Aims: Most research on the widespread phenomenon of nectar robbing has focused on the effect of the nectar robbers' behaviour on host-plant fitness. However, attention also needs be paid to the characteristics of host plants, which can potentially influence the consequences of nectar robbing as well. A system of three sympatric Corydalis species sharing the same nectar-robbing bumble-bee was therefore studied over 3 years in order to investigate the effect of nectar robbing on host reproductive fitness. • Methods: Three perennial species of Corydalis were studied in the Shennongjia Mountain area, central China. Observations were conducted on visitor behaviour and visitation frequencies of nectar-robbers and legitimate pollinators. • Key Results: The results indicated that the effect of nectar robbing by Bombus pyrosoma varied among species, and the three species had different mating systems. Seed set was thus influenced differentially: there was no effect on seed set of the predominantly selfing C. tomentella; for the facultative outcrossing C. incisa, nectar robbing by B. pyrosoma had a positive effect; and nectar robbing had a significant negative effect on the seed set of outcrossing C. ternatifolia. • Conclusions: A hypothesis is proposed that the type of host-plant mating system could influence the consequences of nectar robbing on host reproductive fitness. © The Author 2009. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved.