The relationship between preference and switching in flower foraging by bees

It seems self-evident that generalist foragers switch more between resources than specialists but despite diverse ecological and evolutionary implications, how variation in switching relates to variation in preference warrants additional study. Here we tested predictions based on a simple probability model, using flower-foraging bees as a model system. In laboratory assays, we presented bumble bee (Bombus impatiens) workers with flowers of two species, Tecoma stans and T. alata, from which they could collect nectar and/or pollen. We quantified landing preference and occurrence of switching between species in successive visits. Bees varied greatly in floral preference. Almost half showed statistically significant preferences for one or the other species, while the rest were generalists in preference. As expected, generalists using both flower species switched more in successive visits than bees that were more specialized, a pattern fit to a quadratic function. However, generalist individuals switched more than expected based on null expectation. A Modified Jacob’s Index (MJI) of switching was significantly positively correlated with degree of preference: generalist bees had more negative MJI’s than specialist bees, indicating that even after the expected statistical effect of preference on switching was accounted for, they switched more than specialists. A simulation ruled out the possibility that the pattern was due to bias in MJI. Generalist-specialist differences in which food was collected (nectar versus pollen) were also ruled out. We offer possible explanations for our observed pattern and advocate consideration of preference and switching throughout behavioral ecology.