Floral abundance and resource quality influence pollinator choice

1. Pollinator declines caused by forage habitat loss threaten insect pollination services. Pollinating insects depend on adequate floral resources, and their ability to track these resources. Variability of these resources and the effect on insect foraging choice is poorly understood. 2. We record patterns of visitation to six wildflower species and test the hypotheses that: pollinators preferentially visit the most rewarding flowers; nectar diurnal variations affect foraging preferences; pollinators respond most strongly to nectar rewards. 3. Nectar volume and sugar concentration were negatively correlated within plant species over time of day where greater concentration and lower volume was evident in the afternoon, but this did not correspond to pollinator visitation. Both floral abundance and nectar quality (total sugar per inflorescence) positively affect insect visitation. For some foragers, the positive effects of high quality rewards were only evident when floral abundance was high (>50 inflorescences per patch), perhaps reflecting the low probability of pollinators detecting scarce rewards. Pollen quality (total protein per inflorescence) was negatively related to visitation of Apis mellifera and Bombus pascuorum. 4. Fewer pollinators visiting flowers of higher pollen quality could reflect plant allocation trade-offs or the presence of secondary metabolites in pollen, meaning pollen foraging is likely affected by factors other than protein concentration. Nectar rather than pollen appeared to be the main driver of floral choice by insects in this system. 5. Conservation schemes for bees in farmland or gardens might benefit from ensuring that rewarding plant species are present at high density and/or are aggregated in space.