Plants commonly respond plastically to cues from antagonists and pollinators. Nectar robbery frequently reduces plant reproductive output and shows high spatiotemporal variability, so it seems likely that plants should demonstrate plastic responses to nectar robbery. Plant responses to nectar robbery have been considered most often for semelparous species, with less attention paid to species that flower more than once. It is likely that iteroparous species respond differently to nectar robbing – by, for example, reducing allocation to reproduction when nectar robbing intensity is high – yet whether this actually occurs remains unknown.
I investigated a population of Odontonema cuspidatum –a hummingbird-pollinated iteroparous shrub – experiencing high levels of nectar robbery from stingless bees, to ask whether O. cuspidatum individuals demonstrate plasticity in floral traits in response to nectar robbery, and, if so, whether this plasticity influences subsequent nectar robbing and/or pollination. Using field surveys of 66 marked plants over 3 years, as well as experimental manipulation of potted plants, I asked whether floral traits known to mediate attraction of both pollinators and nectar robbers show evidence of plastic response to nectar robbery.
Results/Conclusions
O. cuspidatum plants demonstrated plasticity in flower number both within and across years, apparently in response to nectar robbery. Within a flowering season, plants experiencing high levels of nectar robbery tended to reduce flower production and end the bloom period more quickly than similar plants experiencing less nectar robbery. In turn, nectar robbing intensity in year 1 was associated with increases in flower production between year 1 and year 2, suggesting that plants anticipate high interannual variability in nectar robbing intensity. Season-long average rates of nectar robbery were negatively correlated across years; that is, O. cuspidatum individuals experiencing high levels of nectar robbery one year experienced a reduction in nectar robbery the following year, and vice-versa. Nectar traits, on the other hand, showed little variation either within or between years in response to nectar robbery.
O. cuspidatum does respond plastically to cues from nectar robbers, apparently in order to ameliorate the negative effects of nectar robbery on reproduction. This plasticity is likely responsible, at least in part, for the wide range in floral display size seen in this population. I conclude with notes about the potential importance of plastic responses to nectar robbery in plant populations more generally.