Nectar thieves influence reproductive fitness by altering behaviour of nectar robbers and legitimate pollinators in Corydalis ambigua (Fumariaceae)

Summary A pollination system whereby nectar resources are shared by nectar robbers, legitimate pollinators and nectar thieves, with interactions among the various types of flower visitors, was studied in a self‐incompatible ephemeral perennial herb, C orydalis ambigua , in north‐east C hina. We conducted a three‐year study in nine populations, using a combination of observations, cages to exclude different combinations of flower visitors, and collars, on flowers to prevent nectar robbing. The results showed that queens of the bumblebee B ombus hypocrita sapporensis , a robberlike pollinator, had higher pollination efficiency in C . ambigua than the legitimate bee pollinators, A pis cerana and A nthophora melanognatha , which served as pollinators for inflorescences that had nectar thieves. Midges of the genus S catopse (nectar thieves) frequently entered host flower spurs to forage for nectar and also mated there. Because nectar robbers avoided visiting nectar‐thieved flowers or inflorescences, the nectar‐thieved inflorescences experienced lower seed productivity. Furthermore, there was a negative relationship between the frequencies of nectar‐thieved and nectar‐robbed inflorescences in the nine natural populations investigated. Results of controlled experiments showed that the varied flower‐visiting modes by different visitors influenced the plant's seed production. Synthesis . Although nectar theft is not uncommon, its consequences for pollination have not been well studied, particularly in the context of an interaction web. Our results demonstrate that, especially in systems that include a mix of legitimate pollinators, nectar robbers and nectar thieves, an experimental approach is required to dissect their various effects on plant fitness.