Local population size and short-term dispersal distance in an orchid bee (Hymenoptera: Euglossini) community in Costa Rican wet forest

Background/Question/Methods

Orchid bees (Hymenoptera: Euglossini) are important pollinators of orchids (Orchidaceae) and other plants in Neotropical forests.  Previous studies have suggested that euglossines are capable of moving long distances (up to 5 km per day), and therefore are not particularly susceptible to the effects of forest fragmentation.  However, these conclusions have been based on limited observations that emphasize maximum distances moved by larger species of euglossine.  We investigated the short-term movements of several species of the most common euglossine species at the La Selva Biological Station in the rain forest of northeastern Costa Rica.  Two marking stations were established 1750 m apart in the forest.  Male euglossines collect scent for mate attraction, and readily visit specific artificial scents.  We used scent baits to attract male bees, which were then captured by net and marked with Liquid Paper© correction fluid.  Bees were recaptured at the two marking stations as well as two other locations in between them. 

Results/Conclusions

We marked 842 males of seven euglossine species over nine days.  The overall recapture rate was 10.3%, substantially higher than previous studies.  Two medium-sized species dominated the sample.  Euglossa championi was common at both stations, with a local population size of 340 (95% confidence interval 222 - 518) at one site and 400 (270 - 588) at the other.  Euglossa imperialis was recaptured at only one site, with a local population size estimate of 490 (301 - 793).  These two species were occasionally recaptured 500-600 m from where they were marked, but only one individual of each species was recaptured >1000 m away.  These two euglossine species had large local populations, but short-term movement was fairly limited compared to published estimates for larger species.  We also captured 14 individuals of a much larger euglossine species, Eulaema meriana; three were recaptured at our maximum sampling distance of 1750 m. Extensive movements considered typical of euglossines may have been biased by data from large species.  The smaller species that dominate euglossine communities are likely to be characterized by more limited dispersal.  As a result, euglossines may be more affected by forest fragmentation and less effective at long-distance pollination than previously suggested.