A recipe for weed disaster in islands: a super-generalist native pollinator aided by a ‘Parlourmaid’ plant welcome new arrivals in Fiji

Abstract

In isolated islands with low pollinator diversity, it has been suggested that native pollinators should evolve into super-generalists that could facilitate the spread of exotic plant species that might otherwise rely on specialist pollinators. Consequently, in the absence of exotic pollinators isolated islands may still be particularly vulnerable to a wide variety of introduced plants. Fiji has a highly abundant and diverse introduced plant fauna, as well as a variety of introduced bee species, but has extremely low endemic bee fauna diversity. We examined bee–plant pollination networks in lowland regions of Viti Levu (Fiji) where there is only one endemic bee species, Homalictus fijiensis. We show that this bee is a super-generalist for introduced plants, and whilst introduced bee species can show high intensities of floral visits, they do not substantially increase the breadth of weeds receiving bee visits. Surprisingly, one introduced plant species, Sphagneticola trilobata, receives high visitations from introduced bee species, even though it spreads vegetatively. We regard this species as a ‘Parlourmaid’ weed that likely augments the spread of exotic bees without gaining pollination benefits. Our results indicate a ‘twofold’ promotion of invasive species, namely, super-generalist native pollinators can promote the spread of diverse introduced plants, and Parlourmaid plants provide resources that can promote the spread of introduced pollinators.