Pollinator-prey conflict in two Drosera species differing in inbreeding level

Background/Question/Methods

Carnivorous plants use insects not only as prey but also as pollinators. If a carnivorous plant uses the same species of insects as prey and pollinators, it may trap pollinators as prey and suffer lower pollination success. This conflict is called Pollinator-Prey Conflict (PPC). In spite of the possibility of PPC, there are some carnivorous plants in which traps and flowers are separated neither spatially nor temporally. It remains unknown how those species could avoid or resolve PPC. PPC could be avoided if a carnivorous plant is highly selfing and has no inbreeding depression; then, catching pollinators could be advantageous in getting nutrients without any decrease of seed production. We used two species of Drosera spp. in different level of selfing (Drosera makinoi and Drosera toyoakensis: D. makinoi is more selfing species) and determined if there were any difference in pollinator-prey overlap level between two species. We recorded the species of pollinators in both species to calculate the rate of pollinator-prey overlap. I compared the number of prey insects in patches where flowers were experimentally removed with that in control patches where flowers were retained. Also, I observed the number of prey insects before a flowering season. 

Results/Conclusions

The proportion of pollinator-prey overlap was higher in more selfing species D. makinoi than in D. toyoakensis. The major pollinator species was hover flies Sphaerophoria philanthus in both species, and they were more likely to be caught in more selfing species D. makinoi than in D. toyoakensis. The positive effect of pollinator attraction by flowers of Drosera was not observed in both Drosera spp.　In this research we demonstrated that the number of trapped pollinators are collated with the selfing level of a carnivorous plant species.