The combined effects of resource landscapes and herbivory on pollination services in agro-ecosystems

Pollinator activity is affected by landscape-scale flower availability, and by pollinator interactions with co-occurring organisms. Of special interest are potentially detrimental effects of herbivores on the attractiveness of plants to pollinators. While insect herbivores are abundant in natural and agro-ecosystems, the combined effect of herbivory and landscape floral resources on pollinator activity and the delivery of pollination services is little studied and understood. Here we investigated the combined effects of surrounding flower cover and aphid herbivory on pollination services in agricultural landscapes. We apply a resource landscape approach for mapping the spatial distribution of floral resources across landscapes, using neighbourhood modelling and empirical data on flower availability in specific land-use types. In each of 25 Mediterranean landscapes spanning a gradient of land-use intensity ranging from natural to agricultural, we established paired patches of potted aphid-infested or aphid-free phytometer plants Diplotaxis erucoides. In each patch, we recorded the activity of insects visiting flowers and subsequent seed set. We also recorded the relative abundance of flowers in dominant land-use locales within a 1 km radius of each patch. Neighbourhood analyses revealed that plant-pollinator interactions in our study system are shaped by herbivory, distribution of floral resources across the landscape, and the interaction between these factors. We found a negative competitive effect of flower cover on pollinator activity and phytometer seed-set; this effect was stronger on aphid-infested than aphid-free plants. The main pollinator guilds in the study sites (wild bees, honeybees and non-bee pollinators) responded differently to these factors. Our results highlight the importance of combining a resource landscape approach with the exploration of interactions among different organisms, when mapping pollination services and identifying the scale at which pollinators respond to foraging resources.