Co-flowering plant species can experience positive (facilitation) or negative (competition) interactions with pollinators, depending on the relative abundance and diversity of plant species and the foraging behavior of their pollinators. Understanding how plant-pollinator networks change through time is particularly important in cropping systems, such as apples, which produce a mass of flowers for a very short time. Mass flowering crops demand high pollinator visitation, but often have co-flowering species both within the orchard and in the surrounding landscape. We compared the degree of overlap between pollinator networks on two varieties of apple (Granny Smith and Pink Lady) and co-flowering plant species both within orchards and in the wider vegetation matrix in two apple growing regions (Orange and Bilpin) in Australia. We surveyed plant-pollinator interactions at key time points during the cropping cycle: before mass flowering, during king, peak and late blooms and, finally, after apple bloom.
Results/Conclusions
Overall, there was considerable overlap in the flower visitor assemblage on apples and on co-flowering species within the orchard, as well as considerable variation between years and between the key time points within a year. Interestingly, the introduced honeybee (Apis mellifera) was the most frequent flower visitor to all three vegetation types at all times in Orange. However, in Bilpin the most apple flower visits were attributable to two species – a native stingless bee (Tetragonula carbonaria) and the honeybee. In both Orange and Bilpin numerous native bees, flies, moths and butterflies and Lepidoptera also commonly visited apple flowers and co-flowering species within the orchard. We found a significant positive correlation between native bee visitation to apple flowers and co-flowering plant species richness, both within the orchard and wider matrix, suggesting a facilitative interaction. However, there was no significant correlation between co-flowering species richness and honeybee visitation to apple flowers. Typically, very few flower visitors were seen in the surrounding native vegetation matrix in Bilpin, although greater flowering output within the orchard led to higher rates of visitation and diversity than in Orange. This study highlights the dynamic nature of plant-pollinator networks and demonstrates the need for studies to examine appropriate temporal scales, especially in cropping systems that undergo mass bloom.