Spillover of pollinators between crops: Competition or facilitation?

Pollination in agroecosystems is a critical ecosystem service that impacts the yield of more than 70% of globally important crops. The movement of pollinators from natural to managed systems is well characterized but the consequences of pollinator spillover from managed systems to natural areas or between managed crops are still poorly studied. In this study we investigate the spillover effect of pollinators between crops with overlapping bloom periods. Specifically, we determine whether mass blooming apple (Malus domestica) facilitates or competes with cultivated strawberry (Fragaria ananassa) for pollinators. Pollinator abundance and richness as well as fruit set of sentinel strawberry plants was measured during early, peak and late apple bloom in 13 landscapes in central NY, USA representing a gradient of 0 to 30% apple cover. The proportion of apple in the landscape had no impact on the weight of strawberry fruits in early apple bloom, a negative effect during peak apple bloom and a positive effect following apple bloom. Our results suggest that mass blooming apples compete with strawberry for pollinators when both crops are blooming concurrently, however we found evidence that pollinators spillover to strawberry following apple bloom.  Our findings indicate that mass blooming crops can have a negative impact on the yield of other flowering crops that require pollinators during the mass flowering period but choosing varieties that do not overlap may boost yields.