Pollinator Foraging Behavior and Gene Dispersal in Senecio (Compositae)

Abstract

The foraging behavior of butterflies and bumblebees is compared on the same populations of 3 Senecio spp. While bumblebees typically fly near-neighbor distances, resulting in very localized pollen dispersal, butterflies frequently bypass nearby plants, flying significantly greater distances between plants. Bumblebees visit significantly more heads per plant and significantly more plants per foraging bout. The flight distance distribution data are used to calculate neighborhood size and area, in the sense of Wright''s isolation-by-distance model, for the observed populations under hypothetical conditions of exclusive butterfly or exclusive bumblebee pollination. Small neighborhood sizes may typically be found in plant populations specializing on bumblebee pollination, whereas butterfly-pollinated populations may have much larger neighborhood sizes; bumblebee-pollinated plants may have greater potential for local genetic differentiation. These differences in neighborhood characteristics may be augmented if plants are self-compatible or if pollen carryover occurs, since bumblebees make a higher proportion of intraplant flights. The addition of a small amount of butterfly pollination can increase gene dispersal in a plant population sufficiently to greatly reduce genetic drift and microgeographic adaptive differentiation.