Assessing drivers of dispersal for bees in fragmented landscapes

Background/Question/Methods

Habitat fragmentation threatens biodiversity by reducing resource availability and population connectivity. For organisms living in fragmented landscapes, population persistence depends on dispersal to maintain genetic variation within populations. Understanding patterns of dispersal for bees is critical given their role as important pollinators of wild plants and agricultural crops, as well as the increasing concern over population declines due to habitat fragmentation. We explored if interspecific variation in bee body size is associated with levels of dispersal across a fragmented landscape in southern Costa Rica, and if these patterns are driven by landscape variables. We used ddRADseq to characterize levels of gene flow and genetic diversity for ten Euglossine bee species that vary in body size, from 9 mm to 28 mm. We also estimated geographic distance between fragments as well as the amount of forest cover surrounding and between fragments.

Results/Conclusions

Species differed in their levels of dispersal among and genetic diversity within forest fragments. Surprisingly, gene flow was more restricted for the larger bee species, Eulaema bombiformisand Eulaema meriana. Geographic distance and forest cover did not predict patterns of gene flow for any of the species studied. We also found differences among species in the way that forest cover affected genetic diversity. We discuss the roles of body size and landscape in shaping patterns of dispersal for Euglossine bees. In particular, our work suggests that body size may not be a useful proxy for predicting vulnerability or resilience of bees living in fragmented landscapes.