The effects of predation risk from crab spiders on bee foraging behavior

Recent studies have suggested that top-down effects of predation on plant-pollinator interactions may not be, as previously thought, rare and/or weak. In this paper, we explore the effects of crab spiders (Araneae: Thomisidae) on the behavior of 2 species of bee (Hymenoptera: Apidae) foraging for nectar and pollen on 3 different plant species in central Portugal. In 2 experiments, we found that the eusocial bee Apis mellifera was significantly less likely to inspect and accept a flower or inflorescence if it harbored a spider. In contrast, we found no such effects of spiders on the behavior of the solitary bee Eucera notata. Further experiments showed that the effects of environmental cues associated with predators on flower visitation by A. mellifera were detectable even when no spider was present at the moment a flower was encountered. Such indirect effects were only identified, however, in bees foraging on 1 of 2 plant species studied. In a final experiment, A. mellifera was shown to respond negatively to the presence of the corpses of conspecifics glued to flowers. This suggests that prey corpses left exposed on petals or bracts by spiders provide an obvious cue that bees can use to avoid predators. These results add to a growing body of evidence that plant-pollinator interactions are not immune to the effects of predation and suggest that the strength of such effects vary both between and within species.