The effect of floral trait variation on pollinator foraging behaviour

Pollinator foraging behaviour has long been seen as tightly linked to the astounding diversity of floral traits exhibited by Angiosperms; however, the precise nature of the relationship between floral trait diversity and pollinator foraging behaviour is somewhat unclear. In this study, three separate series of experiments investigated the effect of floral trait variation on pollinator foraging behaviour.; Using naive bumblebees (Bombus impatiens) foraging on arrays of artificial flowers, the first series of experiments tested the Trait Variability hypothesis for flower constancy in pollinators. The hypothesis predicts that pollinators should exhibit more flower constancy when flowers differ in multiple traits (variation among floral traits) than when flowers differ within a single trait (variation within a floral trait) because multi-trait floral information is more difficult to process. As predicted by the hypothesis, bees showed a high degree of flower constancy and reduced foraging efficiency only with an increase in the number of variable floral traits and not with increases in the amount of variation within a single floral trait.; The second series of experiments examined two potential ethological isolating mechanisms in Mimulus cardinalis and M. lewisii by detailing the flower choices and foraging patterns of naive bumble bees (Bombus impatiens) visiting mono- and heterospecific floral arrays. In contrast to the most commonly held view that a taxon-level pollinator preference for specific floral traits is sufficient to prevent hybridization in this system, the results suggested that in terms of bumble bee foraging behaviour, individual flower constancy induced by differences in the floral traits between the two species is likely the mechanism of ethological isolation in this system.; The final series of experiments was a comparative study of honey bee (Apis mellifera) and bumble bee (Bombus impatiens) foraging behaviour. Using arrays of artificial flowers, three components of honey and bumble bee foraging behaviour were directly compared: flower constancy, flower switching and flower handling ability. Honey bees and bumble bees were found to differ in all three components.; The results of the three series of experiments suggest that variation in floral traits plays an integral role in the foraging decisions made by pollinators. These results are discussed in relation to pollinator cognitive abilities, floral evolution, and plant speciation and community structure.