Individual bee habits cause positive pollination interactions between plant species separated in time

Individuals of some pollinator species, including bumble bees, commonly revisit small areas habitually to forage on a favorite plant species. However, it is unknown how such individual area-fidelity can impact plant pollination. When a bumble bee’s favorite forage plant goes out of bloom in an area, because of this tendency towards area-fidelity, it may be more likely to stay in an area and switch forage plant species rather than search elsewhere for its preferred plant. A newly blooming plant species may therefore quickly adopt a set of loyal visitors from a previous plant species, and thus experience higher pollination success, compared to areas where the first species did not bloom. To test this, we conducted a field experiment in which we manipulated the placement and timing of Delphinium barbeyi and sequentially blooming Gentiana parryi and recorded the behavioral and visitation response of uniquely marked shared bumble bees. We show that many bee individuals returned repeatedly to areas to forage on Delphinium. When Delphinium was experimentally taken out of bloom, the most common response was for area-constant individuals to stay and switch to Gentiana. Due to this behavior of individuals, Gentiana received higher visitation and stigma pollen loads in areas where Delphinium was previously flowering, compared to areas where Delphinium was still flowering or never occurred. Overall, we show that individual bumble bees are habitual in where they forage, and that this can cause a plant species to positively influence the pollination of another, even when they are separated in time.