Plant- pollinator relationships provide a critical ecosystem service. Plants depend on pollinators to set seed and reproduce, and many animal populations rely on the resources provided by flowering plants, such as nectar and pollen. There is an urgent need to document thermal range tolerances and thermal specialization in tropical bee assemblages to understand how these important pollinators may respond to warming temperatures, as tropical ectotherms are expected to be the most vulnerable group to warming temperatures. Our long-term study (2012-2018) aims to quantify patterns of elevation range specialization and peak abundance in tropical bee communities. We focus on seven bee species from the most abundant bee tribe collected, Tribe Ceratinini, as a model group, as members of this tribe span a variety of sizes and functional roles.
Three replicate elevational transects spanning 800 to 1100 m above sea level were established in 2012 in the seasonally dry Pacific slope forests of Costa Rica. The study area represents a mixture of smallholder farms, pasture and forest patches, and is located in a conservation area. Bees were sampled at each 100m elevation change using bee bowls, vane traps, and by hand collecting.
Results/Conclusions
A distance-based redundancy analysis indicates that elevation explains 26% of the variation in Ceratinini community composition for bees collected between 800 and 1100 m elevation (Fpseudo(1,10) = 3.71; P = 0.033). The two smallest (<3.5mm long) most abundant species, Ceratina trimaculata and C. rectangulifera, with over 2,500 individuals collected, both display a high degree of thermal range specialization, with C. rectangulifera’s peak at lower elevations (800-900m elevation) and C. trimaculata’s peak at higher elevations (1100m elevation). The less common and larger (4-11mm long) Ceratinini species also show thermal range specialization, for example the largest collected (11mm long) Ceratina species Ceratina eximia has only been collected at or below 1000m elevation in the study area.
Mountain-dwelling species are expected to exhibit shifts to higher elevations and cooler temperatures over time due to global temperature increases. Given that C. trimaculata peak at 1100m, this species and other thermal specialists may experience population decline or extinction risk in the near future due to loss of habitat resulting from warming temperatures. Our study also provides preliminary evidence that interannual variation in Ceratinini abundance may be driven by rainfall patterns, implying high vulnerability of Ceratinini to more erratic and changing patterns of precipitation.