Resource partitioning among a pollinator guild: A case study of monospecific flower crops under high honeybee pressure

Resource partitioning is a key ecological mechanism allowing species sharing similar resources to limit competition and coexist. Pollinator communities in European agricultural landscapes are ideal models to study resource partitioning, as floral resources are often limited and honeybees, potential competitors, are widespread. Mass-flowering crops can provide abundant resources to pollinators, but spatio-temporal exploitation and resource use by wild pollinators in the presence of a managed competitor is poorly studied. Understanding how wild flower-visiting insects can exploit resources provided by crops under high honeybee abundances is primordial to tailor our management strategies to the conservation of those beneficial insects. In this study, we explored the spatio-temporal resource exploitation of four pollinator morphogroups (the honeybee Apis mellifera, small wild bees, large wild bees and hoverflies) on two uncommon monospecific summer flower crops (cornflower and arnica) in an environment containing a high density of honeybee hives. Our results showed that Apis mellifera was the dominant flower visitor; wild pollinators were also present, but most of them were common and generalist foragers. Moreover, results demonstrated a differential use of the flower crops by the four morphogroups: hoverflies foraged earlier in the day compared to honeybees, and wild bees exploited preferentially cornflower extrafloral nectaries, which are spatially separated from the flowerheads, while honeybees preferred floral resources. Intensive extrafloral nectar visitation by wild bees was a surprising result and may be a mechanism limiting exploitative and interference competition with honeybees. Our study urges to consider simultaneously the quality of the flowers to implement and the potentially negative outcomes of intensive beekeeping practices to sustain wild pollinator communities in agroecological landscapes.