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Steffan-Dewenter I, Münzenberg U, Tscharntke T.Steffan-Dewenter I, et al.Proc Biol Sci. 2001 Aug 22;268(1477):1685-90. doi: 10.1098/rspb.2001.1737.Proc Biol Sci. 2001.PMID: 11506681Free PMC article.