Hefty Vs Wimpy: A Biomechanical Hypothesis For Plant Pollinator Associations

Although research has suggested that biomechanics of flowers are linked to energetics in pollinator foraging behavior, no studies have quantified foraging choices based on differences in biomechanics among floral species.. Here we examined pollinator foraging behavior on the co-occurring clover species Trifolium parryi and T. dasyphyllum, which naturally differ in stem strength and overall sturdiness. We documented foraging behaviors of the long-tongued alpine bumblebee Bombus balteatus, which readily forages on either Trifolium species but normally prefers the sturdier T. parryi. Through artificial manipulation of stem and pedicel sturdiness of the weaker clover, T. dasyphyllum, we tested whether flower biomechanics influence foraging transitions and proportion of visits between the two clover species. Queen B. balteatus foraging in mixed species arrays with altered T. dasyphyllum flowers demonstrated increased preference for and fidelity to T. dasyphyllum compared to queens foraging in control arrays. Overall, strengthening the weaker flowers resulted in queens demonstrating random foraging among T. dasyphyllum and T. parryi inflorescences. These results suggest that floral preferences of long-tongued pollinators such as B. balteatus are driven by biomechanical aspects of the flowers.