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Pérez-Barberia FJ, Elston DA, Gordon IJ, Illius AW.Pérez-Barberia FJ, et al.Proc Biol Sci. 2004 May 22;271(1543):1081-90. doi: 10.1098/rspb.2004.2714.Proc Biol Sci. 2004.PMID: 15293863Free PMC article.