Fatal attraction: flowers lure pollinators as prey in the carnivorous Drosera hookeri (Droseraceae)

Pollinator-prey conflict can occur in carnivorous plants when they ensnare pollinators in their trap-leaves. While spatial or cue separation often abates this conflict, this study investigates Drosera hookeri, which produces flowers in close proximity to leaf-traps. We evaluate pollinator-prey conflict and test the hypothesis that flowers facilitate pollinator capture.

Field studies were conducted between 2007 and 2021 in eastern Australia; the extended duration was necessary because drought conditions often caused sparse flowering or prevented plant emergence. Pollinator diversity and visitation were assessed using video monitoring, and pan-traps estimated community abundance. Hand-pollination experiments determined pollinator dependence and pollen limitation. Arthropod abundance in trap-leaves was measured before, during, and after flowering, and a paired experiment compared prey capture between plants with and without flowers.

Drosera hookeri is highly autofertile and self-compatible, with weak pollen limitation under field conditions. We observed a pollinator-prey conflict: pollinators (predominantly Melangyna viridiceps) accounted for 57% of identified prey, indicating that flowers and nearby trap leaves overlap in their effects. Pollinators were not attracted to plants lacking flowers. In flowering plants, pollinators were occasionally tipped into traps when flimsy pedicels-hypothesised to respond to water stress-bent under their weight.

Drosera hookeri exhibits a pollinator-prey conflict in a resource-limited system. Pollinator capture appears to result from foraging behaviour and floral proximity rather than direct attraction to traps, contrasting with suggestions that pollinators avoid traps due to 'intelligence' or that Drosera mucilage is optimised for smaller prey. Its impact is likely asymmetric, with stronger potential effects on male function through loss of pollen vectors, whereas female function is buffered by autonomous selfing.