Abstract
Wild bees are essential pollinators whose survival partly depends on the capacity of their environment to offer a sufficient amount of nectar and pollen. Semi-natural habitats and mass-flowering crops such as oilseed rape provide abundant floristic resources for bees. The aim of this study was to evaluate the influences of the spatial distribution of semi-natural habitats and oilseed rape fields on the abundance and the mean body size of a solitary bee in grasslands. We focused on a generalist mining bee, Andrena cineraria, that forages and reproduces during oilseed rape flowering. In 21 permanent grasslands of Eastern France, we captured 1 287 individuals (1 205 males and 82 females) and measured the body size of male individuals. The flower density in grasslands was quantified during bee captures (2016) and the landscape surrounding grasslands was characterized during two consecutive years (2015 and 2016). The influence of oilseed rape was tested through its distribution in the landscape during both the current year of bee sampling and the previous year. Bee abundance was positively influenced by the flower density in grasslands and by the area covered by oilseed rape around grasslands in the previous year. The mean body size of A. cineraria was explained by the interaction between flower density in the grassland and the distance to the nearest oilseed rape field in the current year: the flower density positively influenced the mean body size only in grasslands distant from oilseed rape. A. cineraria abundance and body size distribution were not affected by the area of semi-natural habitats in the landscape. The spatial distribution of oilseed rape fields (during both the current and the previous year) as well as the local density of grassland flowers drive both bee abundance and the mean value of an intraspecific trait (body size) in permanent grasslands. Space-time variations of bee abundance and mean body size in grasslands may have important ecological implications on plant pollination and on interspecific interactions between pollinators. Specifically, a competition between bee species for nesting sites might occur in oilseed rape rich landscapes, thus raising important conservation issues for bee species that do not benefit from oilseed rape resources.
Highlights
Bees represent approximately 20 000 species worldwide that participate to the pollination of 87.5% of angiosperm species [1,2]
The abundance of A. cineraria was positively influenced by the %OSR in the previous year and by the flower density in permanent grasslands (Table 1)
The abundance of A. cineraria increased by 107% when the flower density increased from 0 to 50 flowers m-2 (Fig 1B). %SNH only marginally affected abundance while the distance to OSR in the current year was not retained in the final model
Summary
Bees represent approximately 20 000 species worldwide that participate to the pollination of 87.5% of angiosperm species [1,2]. This monophyletic group is characterized by a large variety of morphological, phenological and behavioural traits. These functional traits differ from one species to another, but can vary at the intraspecific level [3,4]. Foraging range was related to body size in bees at the interspecific level [5,6], but may vary with intraspecific body size variation as was shown for pollination efficiency [8,9]. Since bee individuals within species can have various foraging ranges, they differ in the way they respond to the resources located in the surrounding landscape [7]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
