Effects of nectar robbing on pollinator behavior and plant reproductive success of Pitcairnia angustifolia (Bromeliaceae)

Nectar robbers may have direct and indirect effects on plant reproductive success but the presence of nectar robbing is not proof of negative fitness effects. We combined census data and field experiments to disentangle the complex effects of nectar robbing on nectar production rates, pollinator behavior, pollen export, and female reproductive success of Pitcairnia angustifolia. Under natural conditions flowers were visited by four different animal species including a robber‐like pollinator and a secondary robber. Natural levels of nectar robbing ranged from 40 to 100%. Natural variation in nectar robbing was not associated with fruit set in any year whereas seed set was weakly positively associated for 1 year only. Artificial nectar robbing did not increase nectar production or concentration, did not affect the behavior of long‐billed hummingbirds, and when faced with artificially robbed flowers, these visitors behaved as secondary nectar robbers. The number of stigmas within a patch that received pollen dye analogs and the average distance traveled by these analogs were not significantly different between robbing treatments (robbed flowers versus unrobbed flowers), but the maximum distance traveled by these pollen analogs was higher when nectar robbing was not prevented. Overall, the proportion of robbed flowers on an inflorescence had a neutral effect to a weak positive effect on the reproduction of individual plants (i.e. positive association between nectar robbing and fruit set in 2002) even when it clearly changed the behavior of its most efficient pollinator potentially increasing the frequency of nectar robbing within a plant.