The Relationship Between Preference and Switching in Flower Foraging by Bees

Abstract

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. 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 Jacobs Index (MJI) of switching was significantly positively correlated with degree of preference: generalist bees had more negative MJIs 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 discuss possible explanations for our observed pattern and outline possible ways in which preference and switching frequency will interact to shape pollinator behavior and the floral resource. Significance statementBehavioral preference is the subject of a large literature in areas such as foraging, mating and communication. However, a preference measure alone does not necessarily tell us if choices for one alternative are made in runs or intermingled with choices for another alternative. The distinction between preference and the sequential pattern of choices is relevant in many contexts in behavioral ecology but has been a particular focus of study in flower foraging by pollinators. Even in that literature, the relationship between preference and sequential pattern in switching warrants further examination. In our study, bees were shown to vary in preference for flowers of two species. Some were generalists; some were specialists on one or the other species. Generalist bees switched more than specialist bees, even after controlling for statistical effects of preference on switching frequency. The report of this generalist-specialist pattern in switching may be novel and has far-reaching implications throughout the field of behavioral ecology.