Patterns of flower visitor abundance and fruit set in a highly intensified cereal cropping system in a Mediterranean landscape

In intensive agricultural landscapes, decreased pollinator numbers have often been attributed to the loss of natural habitats. However, several studies show that certain mass flowering crops, such as oilseed rape (OSR), can alter the pattern of pollinator abundance at a field and landscape level. These studies have focused mainly on bees; information about the effect of OSR crops on other taxa is missing. We evaluated the abundance of bees and other (non-bee) flower visitors, and the fruit set of insect-pollinated target plants (Raphanus sativus and Onobrychis viciifolia) on the margins of OSR and cereal fields in landscapes with varying densities of non-cropped habitats (landscape structure). The presence of OSR crops and wildflower resources in field margins had varying effects on the abundance of bees and non-bee flower visitors. Bee abundance was enhanced by OSR crops, but decreased in complex landscapes. On the other hand, the abundance of non-bee flower visitors depended on the landscape structure, particularly on the location of cereal fields. Despite the numerous and diverse communities of pollinators attracted by OSR crops and wildflower resources, fruit set was enhanced only for generalist insect-pollinated plant species, because competition processes for pollinators affect specialist plant species. We conclude that the incorporation of OSR crops and maintenance of wildflower resources in agri-environmental schemes should be considered to improve the pollination services in agricultural landscapes highly dominated by cereal fields.