Is There a Latitudinal Gradient in the Importance of Biotic Interactions? Douglas W. Schemske, 1 Gary G. Mittelbach, 2 Howard V. Cornell, 3 James M. Sobel, 4 and Kaustuv Roy 5 1 Department of Plant Biology and W.K. Kellogg Biological Station, Michigan State University, East Lansing, Michigan 48824; email: schem@msu.edu 2 W.K. Kellogg Biological Station and Department of Zoology, Michigan State University, Hickory Corners, Michigan 49060; email: mittelbach@kbs.msu.edu 3 Department of Environmental Science and Policy, University of California, Davis, California 95616; email: hvcornell@ucdavis.edu 4 Department of Plant Biology, Michigan State University, East Lansing, Michigan 48824; email: sobelj@msu.edu 5 Section of Ecology, Behavior, and Evolution, University of California, San Diego, La Jolla, California 92093; email: kroy@ucsd.edu Annu. Rev. Ecol. Evol. Syst. 2009. 40:245–69 First published online as a Review in Advance on August 31, 2009 The Annual Review of Ecology, Evolution, and Systematics is online at ecolsys.annualreviews.org This article’s doi: 10.1146/annurev.ecolsys.39.110707.173430 Copyright c  2009 by Annual Reviews. All rights reserved 1543-592X/09/1201-0245$20.00 Key Words biotic factors, community diversity, latitudinal gradient, species diversity, tropics Abstract Biotic interactions are believed to play a role in the origin and maintenance of species diversity, and multiple hypotheses link the latitudinal diversity gra- dient to a presumed gradient in the importance of biotic interactions. Here we address whether biotic interactions are more important at low latitudes, finding support for this hypothesis from a wide range of interactions. Some of the best-supported examples are higher herbivory and insect predation in the tropics, and predominantly tropical mutualisms such as cleaning symbioses and ant-plant interactions. For studies that included tropical regions, biotic interactions were never more important at high latitudes. Although our re- sults support the hypothesis that biotic interactions are more important in the tropics, additional research is needed, including latitudinal comparisons of rates of molecular evolution for genes involved in biotic interactions, es- timates of gradients in interaction strength, and phylogenetic comparisons of the traits that mediate biotic interactions. 245 Annu. Rev. Ecol. Evol. Syst. 2009.40:245-269. Downloaded from www.annualreviews.org by Universidade de Sao Paulo (USP) on 11/19/12. For personal use only.