Abstract
Pollinators for animal pollinated crops can be provided by natural and semi-natural habitats, ranging from large vegetation remnants to small areas of non-crop land in an otherwise highly modified landscape. It is unknown, however, how different small- and large-scale habitat patches interact as pollinator sources. In the intensively managed Argentine Pampas, we studied the additive and interactive effects of large expanses (up to 2200 ha) of natural habitat, represented by untilled isolated “sierras”, and narrow (3–7 m wide) strips of semi-natural habitat, represented by field margins, as pollinator sources for sunflower (Helianthus annus). We estimated visitation rates by feral honey-bees, Apis mellifera, and native flower visitors (as a group) at 1, 5, 25, 50 and 100 m from a field margin in 17 sunflower fields 0–10 km distant from the nearest sierra. Honey-bees dominated the pollinator assemblage accounting for >90% of all visits to sunflower inflorescences. Honey-bee visitation was strongly affected by proximity to the sierras decreasing by about 70% in the most isolated fields. There was also a decline in honey-bee visitation with distance from the field margin, which was apparent with increasing field isolation, but undetected in fields nearby large expanses of natural habitat. The probability of observing a native visitor decreased with isolation from the sierras, but in other respects visitation by flower visitors other than honey-bees was mostly unaffected by the habitat factors assessed in this study. Overall, we found strong hierarchical and interactive effects between the study large and small-scale pollinator sources. These results emphasize the importance of preserving natural habitats and managing actively field verges in the absence of large remnants of natural habitat for improving pollinator services.
Highlights
Animal-mediated pollination is one of the most critical processes involved in the reproduction of wild and cultivated flowering plants often limiting seed production [1,2]
To our knowledge ours is the first study demonstrating that local edge effects on pollinator visitation can be modulated by larger-scale regional effects
We found that a decrease in visitation by feral honey-bees to sunflower heads occurring at a scale of 100 m from the field margins was not detected on the proximity of large expanses of natural habitats provided by sierras, whereas this local edge effect was apparent in sunflower fields located several kilometers away from the nearest sierra
Summary
Animal-mediated pollination is one of the most critical processes involved in the reproduction of wild and cultivated flowering plants often limiting seed production [1,2]. Because .70% of all agricultural crops depend to some extent on pollinators to maximize their yield [1,3], the pollination service provided by flower visitors nesting or gathering food in neighboring natural or semi-natural habitats has an important role in global food production [4]. The destruction and fragmentation of natural or semi-natural habitat remnants through agricultural intensification are among the main causes of the decrease in local and global biodiversity in general [13], and pollinator abundance and diversity in particular [14,15]. Because many pollinators are far-ranging foragers but prefer to harvest resources locally, their demise can result from compound and interacting effects of habitat destruction and fragmentation occurring at different scales. An understanding of how different small- and large-scale habitat types contribute and interact to sustain vigorous bee populations is of paramount importance to their preservation and, through this mechanism, improve agricultural yield
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