Extreme host range in an insular bee supports the super-generalist hypothesis with implications for both weed invasion and crop pollination

Abstract

Super-generalism is a pollinator trait where species obtain floral resources from a very wide range of plant species. Theoretical and empirical studies suggest that on islands with low pollinator diversity, such pollinators should evolve to exploit a very wide range of floral morphologies. Super-generalism has implications not only for securing pollination network stability, but also for the invasibility of potential weeds that require specialist pollinators in their original ranges. Here we expand earlier studies on bees in Fiji to include a wider range of bee-plant interactions for bees that have been recently introduced into Fiji as well as the endemic Fijian halictine bee, Homalictus fijiensis. Our data show that the endemic Fijian bee has a much wider range of floral hosts than introduced bees, and this extends to pollen larceny of solanoid plant species that are usually buzz pollinated. Importantly, solanoid plants were not visited by introduced bee species, including the honeybee Apis mellifera, which is usually regarded as a super-generalist. Our findings are important because they add critical support to the hypothesis that super-generalism evolves in insular ecosystems with low pollinator diversity and that this may make such ecosystems vulnerable to invasion by exotic weeds. However, insular super-generalists may also have potential to stabilize plant-pollinator networks and may also be effective pollinators for exotic crop species, and this needs to be further explored in agricultural settings.