基金Funding for this study was supplied by the University of Wurzburg and the Land Bavaria. We thank G. Grimmer for provision of solitary bee nests from her property. We also appreciate comments by I. Steffan-Dewenter on the draft of the manuscript.
基金This work was supported by a Ministry of Science and Higher Education （N N311 298935） and University of Life Sciences （507.511.29） grants to O.W. and in part by a National Science Foundation Grant （EPS-0903787, MSU#269110-151250） grant to N.K. We would like to thank Agnieszka Graclik for her technical support in im- age analysis and preparation.