Spatial community turnover of pollinators is relaxed by semi-natural habitats, but not by mass-flowering crops in agricultural landscapes

Understanding beta-diversity, i.e. species turnover in space and time, is essential for informing conservation actions. Soaring cultivation of mass flowering crops (e.g. oil seed rape OSR) and loss of semi-natural habitats (SNH) can strongly affect populations of native pollinators, yet it remains unclear how OSR and SNH affect spatial and temporal turnover of pollinator communities. Here, we examined how the landscape-scale proportions of OSR and SNH affect spatial and temporal community turnover in solitary bees and hoverflies, two key provider groups of pollination and pest control services in temperate agro-ecosystems. Using a novel grid-based landscape-wide sampling approach, we quantified pollinator communities within ten 1 km × 1 km landscapes representing independent gradients in OSR and SNH availability. We sampled during and after OSR flowering, in two subsequent years, yielding app. 8800 specimens representing 160 species. Spatial community turnover, measured as the slope of the dissimilarity-distance relationship, was not influenced by the proportion of OSR at any time. In contrast, SNH decreased community turnover for bees during OSR flowering and for hoverflies after flowering, likely caused by pollinator movement between land use types. This suggests that a high availability of SNH may help to promote an even distribution of native bees and hoverflies within temperate agricultural landscapes, hereby potentially stabilizing landscape-wide pollination services.