Low endemic bee diversity and very wide host range in lowland Fiji: support for the pollinator super-generalist hypothesis in island biogeography

Abstract

The success of invading plants in island ecosystems has often been inferred to result from ‘invader complexes’, where cointroduced plants and their specialist pollinators can reciprocally enhance each other’s spread. However, it has also been suggested that in islands with low pollinator diversity, those pollinators should evolve into super-generalists that may be able to pollinate a wide range of exotic plants, enabling the spread of exotic weeds. Fiji has a very depauperate endemic bee fauna and previous studies have suggested that its only lowland bee species, Homalictus fijiensis (Apoidea: Halictidae), has a very wide range of host plants. However, those studies only included a small number of endemic flowering plants. Our study expands observations of bee–flower interactions to explore host plant ranges of H. fijiensis and introduced bee species to include a wider variety of native and introduced plant species. We show that H. fijiensis does have a wider host range than introduced bees, including Apis mellifera (Apoidea: Apidae), and an ability to exploit extrafloral nectaries and poricidal anthers that are not utilised by the introduced bee species. Our results support the hypothesis that super-generalism can evolve in islands where pollinator diversity is low, and that this may make those islands susceptible to weed invasions.

Radiation of tropical island bees and the role of phylogenetic niche conservatism as an important driver of biodiversity

“…accounting for only 8% and 4%, respectively [30]. Secondly, a generalist diet in Fijian Homalictus enables the use of introduced and weedy plants that may have been brought to Fiji by the earliest human settlers and up until current times [24]. Finally, nesting preference for bare or sparsely vegetated ground indicates likely resilience of these bees to habitat clearing.…”

“…Homalictus species are generally communal ground-nesting species and often generalist pollinators, yet little has been published on their habits [23]. Most Fijian Homalictus species forage on both weedy and native plants, indicating polylectic diets, while H. fijiensis is a super-generalist pollinator [24]. Until recently, only four Fijian species were known, but genetic and morphological studies indicate a much more speciose clade [25], with many species only recorded from high elevations [26].…”

Holocene population expansion of a tropical bee coincides with early human colonization of Fiji rather than climate change

“…For both Viti Levu and Kadavu samples we counted the number of individuals assayed for each unique haplotype. These counts were then used in rarefaction analyses using the EstimateS software package version 9.1.0 for Macintosh (Colwell, 2013). We cal-…”

Island Invasions by Introduced Honey Bees: What Can Be Expected for Puerto Rico and the Caribbean?

“…Puerto Rico where individual interactions can be extracted have not been published (e.g., Martín González et al, 2009González et al, , 2010. As in other islands worldwide (Crichton et al, 2018), Puerto Rico has at least one native super-generalist pollinator, Xylocopa mordax (Apidae), which uses at minimum 375 plant species for food and provides pollinator services for 43 fruit and seed crops (Jackson and Woodbury, 1976;Jackson, 1985). While there are ∼42 bee species among islands of the Puerto Rican Bank (Genaro and Franz, 2008;Genaro, 2016;Gibbs, 2018), their floral resources are largely unknown.…”

“…While there are ∼42 bee species among islands of the Puerto Rican Bank (Genaro and Franz, 2008;Genaro, 2016;Gibbs, 2018), their floral resources are largely unknown. Without knowledge of plant-pollinator communities prior to HB introduction, we can only speculate what impact HB have had on native bees (Paini, 2004;Stout and Morales, 2009), and it may not have been negative as discovered in Fiji (Crichton et al, 2018).…”