Pollinator communities on a landscape complexity gradient in southern Sweden

Abstract: Investigating how pollinator populations are affected by land use changes is crucial for predicting their persistence in the landscape and thereby the persistence of the significant service they provide to crop production. Pollinator populations are subjected to multiple threats, particularly overall intensification of cropping systems and landscape simplification. I investigated how landscape complexity affects pollinator and plant communities, and how pollinators interact with plant species across time. Rough pastures on a gradient of landscape complexity were assessed for ground cover of flowers and of vegetative ground cover of flowering plants, by estimation in 20 squares of one m2 along two flower-rich transects of ten meters in each pasture. They were also sampled for pollinating insects by walking along the same transects and collecting them from flowers. The sites were spread out across Skåne in southern Sweden and sampled in early July, late July and early August of 2017. Significant plant and floral shifts along the sampling period were observed. Floral resources decreased in late summer, potentially triggering population collapse of bumblebees. However, no effects of landscape complexity on plant and pollinator richness were observed. Similarly, I did not find relationships between landscape complexity and the percentage of bumblebees with long tongues (specialist bumblebees). However, there was a trend in higher proportion of female bumblebees, and a higher abundance of a red listed species (Bombus muscorum) in more complex landscapes. My results show no clear relationships between landscape complexity and plant or pollinator richness. However, the positive trend between female bumblebees and landscape complexity suggest that collapse of bumblebee populations is delayed with more diversified floral resources. My results also show the importance of complex landscapes to maximize plant-pollinator interactions, while preserving red-listed species.